UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Quantification of motor unit activity and steadiness in a functional task Cornett, Kayla Margaret Dawn 2013

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
24-ubc_2014_spring_cornett_kayla margaret dawn.pdf [ 1.97MB ]
Metadata
JSON: 24-1.0074310.json
JSON-LD: 24-1.0074310-ld.json
RDF/XML (Pretty): 24-1.0074310-rdf.xml
RDF/JSON: 24-1.0074310-rdf.json
Turtle: 24-1.0074310-turtle.txt
N-Triples: 24-1.0074310-rdf-ntriples.txt
Original Record: 24-1.0074310-source.json
Full Text
24-1.0074310-fulltext.txt
Citation
24-1.0074310.ris

Full Text

QUANTIFICATION OF MOTOR UNIT ACTIVITY AND STEADINESS IN A FUNCTIONAL TASK  by  Kayla Margaret Dawn Cornett  B.H.K, The University of British Columbia, 2011  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQIREMENTS FOR THE DEGREE OF  MASTER OF SCIENCE  in  THE COLLEGE OF GRADUATE STUDIES  (Interdisciplinary Studies)  [Health and Exercise Sciences]   THE UNIVERSITY OF BRITISH COLUMBIA  (Okanagan)    October 2013  ?Kayla Margaret Dawn Cornett, 2013 ii  Abstract  The ability to control functional movement is essential for daily life. Extensive literature exists on lower motor unit (MU) recruitment thresholds and greater discharge rates in anisometric compared with isometric contractions. This difference is in-part related to task specificity. To-date the spinal control of functional movement has not been evaluated relative to the performance of functional movement. The purpose of this thesis was to quantify and evaluate MU activity and steadiness in a functional task compared to anisometric and isometric contractions.  Thirteen female subjects (22.5 ? 2.9 years) were recruited. Surface and intramuscular electromyography (EMG) were recorded from the elbow flexor muscles. Subjects performed 4 experimental contractions; 1. a waterbottle drinking task where subjects lifted a waterbottle, took a sip of water and lowered the bottle (functional task); 2. a waterbottle lifting task performed identical to the previous but without drinking; 3. an anisometric contraction matched for load, range of motion, and acceleration; 4. a load matched isometric contraction. Repeated measures ANOVAs were used to assess EMG, MU recruitment and discharge rates and steadiness between the contractions.    Surface EMG was not different between the three movement tasks but lower during the isometric contraction. The waterbottle drinking task had the highest discharge rate, as well as discharge rate variability and was the least steady. There were no differences in recruitment between the 4 contraction types. This was the first study to evaluate MU activity in functional tasks. It is clear that functional tasks require unique activation strategies which occur primarily through alterations in MU discharge rate. Thus, spinal control is not only task specific, but also related to goal-directed outcomes of the movement.  iii  Preface Ethics approval for this research was granted by the University of British Columbia?s Clinical Research Ethics Board on November 22, 2011. The ethics approval certificate number for the current study is H11-01931. To date, the research included in this thesis has not been published in full. Preliminary results were published and presented in abstract form at national and international conferences.     iv  Table of Contents  Abstract ................................................................................................................................ ii Preface................................................................................................................................. iii Table of Contents ................................................................................................................ iv List of Tables ...................................................................................................................... vi List of Figures .................................................................................................................... vii List of Abbreviations ........................................................................................................ viii Glossary .............................................................................................................................. ix Acknowledgements ............................................................................................................ xii Dedication ......................................................................................................................... xiv Chapter 1: Introduction ........................................................................................................ 1 1.1 Voluntary Movement and the Neuromuscular System .............................................. 1 1.2 Motor Unit Characteristics ......................................................................................... 6 1.3 Task Specificity .......................................................................................................... 8 1.4 Control of Muscle Contractions ............................................................................... 12 1.6 Summary of Literature ............................................................................................. 15 Chapter 2: Aims and Hypotheses ....................................................................................... 17 2.1 Purpose ..................................................................................................................... 17 2.2 Aims ......................................................................................................................... 17 2.3 Hypotheses ............................................................................................................... 17 Chapter 3: Methods ............................................................................................................ 19 3.1 Participants ............................................................................................................... 19 3.2 Experimental Set-Up ................................................................................................ 19 3.3 Experimental Protocol .............................................................................................. 23 3.4 Data Analysis ........................................................................................................... 25 3.5 Statistical Analysis ................................................................................................... 30 Chapter 4: Results .............................................................................................................. 31 4.1 Subjects .................................................................................................................... 31 4.2 Surface EMG ............................................................................................................ 31 4.3 Steadiness ................................................................................................................. 33 4.4 MU Characteristics ................................................................................................... 34 v  Chapter 5: Discussion ........................................................................................................ 38 5.1 Limitations ............................................................................................................... 42 5.2 Future Research ........................................................................................................ 43 Chapter 6: Conclusion........................................................................................................ 45 References .......................................................................................................................... 46 Appendices ......................................................................................................................... 52 Appendix A: Copyright Approval for Figure 4 .............................................................. 52 Appendix B: Ethics Approval ........................................................................................ 53 Appendix C: Pre-Study Questionnaire ........................................................................... 54 Appendix D: Subject Characteristic Data ...................................................................... 56    vi  List of Tables Table 1: Generalization of differences in MU activity between isometric and  anisometric contractions ........................................................................................ 9 Table 2: Maximal voluntary contraction strength .............................................................. 31    vii  List of Figures Figure 1: Voluntary control of muscle contractions ............................................................ 4 Figure 2: Motor unit activity in an anisometric contraction (A) and functional task  (B). ..................................................................................................................... 12 Figure 3: Positional differences in force steadiness of the elbow flexors.......................... 13 Figure 4: Sex differences in elbow flexor force steadiness across submaximal force  levels. ................................................................................................................. 14 Figure 5: Experimental set-up ............................................................................................ 21 Figure 6: EMG and MU set-up .......................................................................................... 22 Figure 7: Representative visual feedback. ......................................................................... 26 Figure 8: Representative surface EMG data analysis. ....................................................... 28 Figure 9: Representative motor unit analysis..................................................................... 29 Figure 10: EMG activity of the long (A) and short (B) head of the biceps brachii  during the 4 different contractions. ................................................................... 33 Figure 11: EMG activity of the brachioradialis during the four different contractions. .... 34 Figure 12: Steadiness during the 5 phases of the dynamic contractions. ........................... 35 Figure 13: Motor unit discharge rate of the long (A) and short (B) head of the biceps brachii during the 4 different contractions ........................................................ 36 Figure 14: Motor unit discharge rate variability in the 4 different contractions. ............... 37 Figure 15: Motor unit recruitment time between the 4 contraction types.......................... 38   viii  List of Abbreviations CV: Coefficient of Variation EMG: Electromyography LH: Long Head MU: Motor Unit MVC: Maximal Voluntary Contraction SD: Standard Deviation SEM: Standard Error of the Mean SH: Short Head    ix  Glossary 1a afferents: A primary sensory afferent fibre which wraps around the nuclear chain and bag fibres of the equatorial region of the muscle spindle. These afferents detect changes in muscle length and rate of change in length, thus they provide information about the velocity and direction of the muscle stretch.  Acceleration: The rate of change of velocity. Action Potential: A change in electrical potential across a cell membrane. For the purpose of this thesis, the primary cells under consideration are nerve and muscle cells. Anisometric Contraction: Dynamic muscle contraction in which the muscle changes length through movement of the joints range of motion. Coefficient of Variation: Ratio of the standard deviation over the average. Represents the variability around the mean of the population. Concentric Contraction: Muscle shortening in the production of force. Corticospinal tract: A group of nerve fibres that carries motor commands from the brain to the spinal cord. Discharge Rate: The firing frequency of action potentials. Discharge Rate Variability: A measure of inconsistency of action potentials from the mean discharge rate of the population. Eccentric Contraction: Muscle lengthening in the production of force. x  Electromyography: Electrical recording of global muscle activity. Heteronymous Muscle: A different muscle. Homonymous Muscle: The same muscle. Indwelling EMG: Electrical recording of a single muscle fibres activity through the placement of wires within a muscle. Isometric Contraction: A muscle contraction in which length and range of motion of the joint remains isolated to a singular position. Motor Neuron: Neurons that send motor command signals from the spinal cord to muscles or other effector organs. Motor Unit: A motor neuron and all of the muscle fibres it innervates. Muscle Spindle: A type of proprioceptor that is responsible for detecting change in muscle length. Located within the extrafusal muscle fibres and composed of intrafusal muscle fibres. Nuclear Bag Fibres: A type of dynamic intrafusal muscle fibre located in the muscle spindle. Nuclear Chain Fibres: A type of static intrafusal muscle fibre located in the muscle spindle. Proprioceptors: Sensory receptors that provide information regarding the position of the body, particularly the musculoskeletal system, in space. xi  Recruitment Threshold: The force, or for the purpose of this thesis the time at which a motor unit is first activated. Steadiness: The ability to maintain a consistent, constant movement without wavering.   xii  Acknowledgements First, and foremost I would like to acknowledge my supervisor, Dr Jennifer Jakobi. Jenn, you are a true inspiration. Your passion for research, dedication to your students and love of your family all gets balanced in an unbelievable way. Thank you for sharing your knowledge with me and helping me grow as a researcher. Thank you for all of your patience, support and understanding throughout these past years. None of this would have been possible without you and I am truly grateful. Next I would like to acknowledge Noelannah and Kaitlyn. Noelannah, thank you for being my second hand throughout all of my data collection. I really appreciate all of the long hours your put in with me. Thank you for all of the good memories in the lab and for being a true friend. I couldn?t have asked for a better person to share this experience with. Kaitlyn, thank you for introducing me to so many aspects of research and helping me learn my way in the field. You were a true mentor to me and I will always look up to you as a researcher. Thank you to my committee, Bruce, Gareth and Paul for supporting me throughout this journey and showing an interest in the research I conducted. To all of my fellow research students, especially the lab next door, thank you for all of the potlucks, weekend trips and outings, laughs and memories that I will always treasure. You made this experience so enjoyable and I can?t imagine any of it without you. To my family, thank you for all of your love and support throughout these past two years. Thank you for always being there for me, helping whenever I needed, listening, and providing some much needed relief during stressful moments of research. I xiii  love you all. Finally, to Hugh. Thank you for all of your love and support, no matter what I choose to do. You are my rock in so many ways ? the person I lean on when things get tough, the person who can make me smile, and the person I can count on. The things you do for me do not go unnoticed; I truly appreciate everything you do.    xiv  Dedication For Great-Grandma. Forever in my heart. 1  Chapter 1: Introduction The ability to perform purposeful tasks such as drinking or pouring water, brushing your teeth and washing your face requires muscle control. This control occurs at many levels of the central and peripheral nervous system with the final point of organizational output being the motor unit (MU). A MU is composed of a single motor neuron and all of the muscle fibres it innervates. Extensive literature exists on MU activity and force control for isometric contractions, but there are minimal scientific reports for MU activity during anisometric contractions and no information on functional movement. Isometric contractions are muscle contractions in which no change in joint angle or muscle length occurs, whereas anisometric contractions involve the joint moving through a range of motion during the muscle contraction. Functional movement also involves the joint moving through a range of motion, but there is a pre-planned objective of executing a task for a goal directed outcome. Each of these types of movements require specific motor programming that is typically initiated from higher order centres in the brain where neural impulses are transmitted down the central nervous system through to the peripheral nervous system where ultimately skeletal muscle generates the programmed action. However, as the action of the task increases in complexity the programming and coordination of the muscular system becomes more involved (Verstynen, Diedrichsen, Albert, Aparicio, & Ivry, 2005). 1.1 Voluntary Movement and the Neuromuscular System The generation of voluntary movement requires processing of information from the brain throughout the nervous system and down to the level of the muscle. The primary motor cortex of the brain sends signals via the corticospinal tract through the spinal cord. The corticospinal tract is one of the largest in the spinal cord and two thirds of its axons 2  originate in the motor cortex (McArdle, Katch, & Katch, 2010). The corticospinal and rubrospinal tracts compose the pyramidal tract which activates skeletal muscles for voluntary control. The extrapyramidal tract, on the other hand, contains axons that originate in the brainstem and control posture and muscle tone. The signals from the primary motor cortex, both excitatory and inhibitory, travel down, for example, the corticospinal tract and converge on the cell bodies of the alpha motor neurons located in the grey matter of the anterior horn of the spinal cord (Seeley VanPutte, Regen, & Russo, 2011). If the nerve cell membrane reaches the threshold potential for excitation of approximately -55mV, an action potential occurs and travels along the axon of the alpha motor neuron to the muscle fibres it innervates (Figure 1). Motor neurons receive inputs from both ionotropic and neuromodulatory inputs (Heckman, Gorassini, & Bennet, 2005). The descending tracts as well as sensory afferent fibres are involved in transmission of ionotropic inputs. These result in neurotransmitters being released and binding to ligand-gated channels to generate excitatory postsynaptic potentials or inhibitory postsynaptic potentials (Heckman, Johnson, Mottram, & Schuster, 2008). Neuromodulatory inputs, on the other hand, involve G protein receptors which activate signalling cascades to alter electric properties of the cell.  Both of these types of inputs together determine the outcome of the motor neurons activity. The area connecting the motor nerve and the muscle fibre is known as the neuromuscular junction. The neuromuscular junction consists of the plasma membrane of the motor nerve, the synaptic cleft or space between the nerve and muscle, and the motor end plate which is located on the sarcolemma of the muscle fibre. The action potential must be transmitted across this junction to successfully reach the skeletal muscle fibres. The action potential in the alpha motor neuron causes acetylcholine which is packaged in vesicles to migrate to the pre-synaptic membrane, dock and fuse to the membrane for 3  release into the synaptic cleft (Seeley et al, 2011). The electrical impulse has now been converted to a chemical stimulus. The acetylcholine crosses the synaptic cleft and attaches to the post-synaptic membrane (located on the muscle fibre). This binding causes the sodium potassium channel to open. Sodium then moves in and potassium slowly moves out. This causes a charge difference across the membrane. When the threshold (-55mV) is reached an action potential occurs and travels through the transverse tubule system. This excitation changes the permeability of the skeletal muscle membrane activating voltage-gated calcium channels. Calcium is released from the sarcoplasmic reticulum and binds to troponin-tropomyosin complex located on the actin filaments of the muscle fibre. The binding of calcium causes the shape of troponin to change removing tropomyosin from the binding sites on the actin filament. This movement opens the binding sites between myosin and actin and initiates cross-bridge formation and cycling between actin and myosin. This cycle of binding and a powerful stroke between actin and myosin with the subsequent detachment of these proteins due to the phosphorylation of adenosine triphosphate is the basis of a cross bridge cycle and generates muscle contraction (McArdle et al, 2010).  4     Figure 1: Voluntary control of muscle contractions The primary motor cortex of the brain sends signals via the lateral corticospinal tract through the spinal cord. The signals cross sides in the medulla oblongata through the pyramidal decussation and travel the opposite side of the spinal cord than the side of the brain where the original signal was initiated. The signals from the primary motor cortex, both excitatory and inhibitory, converge on the cell bodies of the alpha motor neurons, and interneurons (not shown), located in the grey matter of the spinal cord. If threshold is reached, an action potential occurs and travels along the axon of the alpha motor neuron to the muscle fibres it innervates. The area between the end of the motor neuron and the start of the muscle fibre is known as the neuromuscular junction. The electrical impulse is converted to a chemical stimulus which generates muscle contraction.  Two important sensory organs, the muscle spindle and the golgi tendon organ, play an additional and necessary role in the control of voluntary movements. These organs monitor movement and modify subsequent behaviour of the muscles (MacIntosh, 5  Gardiner, & McComas, 2006). The intrafusal fibres of the muscle spindle are important for coordination of planned and learned movements as they provide feedback of changes in muscle length. The muscle spindle is located within the muscle and is composed of intrafusal fibres that are surrounded by the extrafusal muscle fibres. The nuclear bag and nuclear chain intrafusal fibres are proprioceptors that are responsible for revealing information about the static length and rate of change (velocity) of muscle length, respectively. These intrafusal fibres which comprise the muscle spindles are innervated by gamma motor nerves which increase the sensitivity of the muscle spindle to stretch. The necessary output information detected by the muscle spindle travels via the 1a afferent to the spinal cord and synapses onto tracts ascending to the brain, to other motor neurons innervating the homonymous muscle as well as interneurons which synapse with cell bodies of both homonymous as well as heteronymous muscle. These homonymous and heteronymous inputs are organized through polysynaptic interneurons which interact with motor neurons to initiate inhibition and/or excitation of agonist and antagonist muscles on both sides of the body (MacIntosh et al, 2006). The strongest of these connections are made to motor neurons which supply contractile tissue in the same area as the spindle itself. This arrangement allows for functional compartmentalization and may allow certain MUs to be preferentially activated for given tasks. Golgi tendon organs provide further information on muscle forces during normal activities. These proprioceptors are located in the musculotendinous junctions rather than the muscle belly. The golgi tendon organ is most sensitive to changes in contractile force. Thus, both the muscle spindle and golgi tendon organs provide proprioceptive information via reflex feedback to the motor neuron pool to assist in regulating voluntary movement (MacIntosh et al, 2006). 6  1.2 Motor Unit Characteristics A MU is defined as the alpha motor neuron and all of the muscle fibres it innervates. The MU controls muscle contractions through the number of fibres activated (recruitment) and the speed at which they discharge (discharge rate). The cell body of the motoneuron within the spinal cord determines the order in which a MU is activated. MU recruitment is orderly and occurs from the smallest cell body to the largest (Henneman, 1957).  Discharge rate also increases from the lowest level which occurs at recruitment until force is maximal.  The earliest recruited units typically have the highest discharge rates, as defined through the onion skin phenomenon (De Luca and Erim, 1994). MUs are organized in the spinal cord according to the muscle they innervate and potentially via their contribution to various tasks (ter haar Romeny, Denier van der Gon, & Gielen, 1984). The term motor neuron pool describes the group of MUs that innervate a muscle (McArdle et al, 2010). MUs consisting of only a small number of muscle fibres tend to be involved in precise movements, whereas MUs with motor neurons that innervate a large number of fibres are typically involved in more powerful, gross movements. Force control between precision and forceful contractions are generally controlled via recruitment of MUs or rate coding strategies of the recruited MUs. Seki and Narusawa (1996) demonstrated that during precise movements rate coding is predominantly used to control force; however, during the more powerful movements recruitment of MUs is the primary means to regulate force. Functional tasks require more precise movements to complete a task accurately and it is plausible that rate coding strategies might be the primary means for force control. Whereas the more gross, simple anisometric and isometric contractions may not require the same degree of rate coding strategies. Thus, MU discharge rates are likely to occupy a more prominent role in the control of functional tasks. 7  The type of fibre each motor neuron innervates is determined by the classification of the MU. MUs are differentiated through three distinct types; fast fatigable, fast fatigue-resistant and slow. Fast fatigable MUs produce high amounts of force at a high contraction speed; however, they fatigue quickly. The motor neurons of these MUs innervate fast glycolytic muscle fibres. Fast-fatigue resistant MUs produce moderate amounts of force at a high contraction speed and do not fatigue as quickly. The motor neurons of these MUs innervate the fast oxidative glycolytic muscle fibres. Finally, the slow MUs produce low amounts of force at slow contraction speeds and do not fatigue easily. Slow oxidative muscle fibres are included in these MUs. The slow twitch units are generally recruited first as they have the lowest voltage threshold for activation as described by Henneman?s size principal (1957).  Voltage thresholds determine when a MU is activated. Smaller MUs, which include the slow-twitch units, require less depolarization to reach threshold. As the contraction continues the fast-fatigue resistant and fast-fatigable MUs become active which have a higher threshold for activation. This strategy is beneficial for the production and control of movement as the more fatigue resistant fibres are activated first and for the longest period of time. Further it ensures that a smooth force increment occurs because at low efforts smaller units are recruited, thus the change in force occurs in small increments with the primary means of force control being MU discharge rate. As the level of voluntary drive increases, the threshold for activation is achieved and larger MUs becoming engaged. Recruitment of each additional MU results in greater increments in force (Henneman & Olson, 1965; Zajac & Faden, 1985).  Although the size principle is widely accepted by scientists, it has typically been described for slow ramp forces. Current literature indicates that MUs can also be selectively recruited for particular movements. In rapid, powerful movements, fast-twitch 8  fatigue resistant fibres are recruited first instead of slow oxidative fibres and then fast-twitch fatigable fibres follow (McArdle et al, 2010). This differential activation relative to particular movements is further explained by the concept of task specificity. 1.3 Task Specificity  A concept known as task specificity suggests that descending drive and the subsequent MU activity vary depending on the task being performed. Both the intent to perform a specific task and the need for more careful control to properly execute the task may cause neuromuscular control processes to differ between tasks. An example of this can be shown through studies which examined both force and position tasks. In these studies a force task was one in which a subject pulled up against resistance with the arm fixed into a traditional isometric set-up with the joint angle fixed. In the position task, a load was hung from the participants arm and the joint was not fixed, thus the objective of the task was to maintain the initial arm position with a similar load to the force task. The force tasks were found to have significantly higher MU discharge rates than the position task and the force tasks were also steadiest (Hunter, Ryan, Ortega, & Enoka, 2002; Mottram, Jakobi, Semmler, & Enoka, 2005). This suggests that there are different control strategies based on the demand of the task and these strategies in neural activity influence the movement outcome. Supporting evidence for this level of task specificity is also demonstrated through studies which examined isometric and anisometric contractions. Anisometric contractions are more difficult to execute than simple isometric contractions and force control is lower during the anisometric contractions (Burnett, Laidlaw, & Enoka, 2000; Graves, Kornatz, & Enoka, 2000).  Measurement of arm muscles (biceps brachii, brachioradialis, and anterior deltoid) in loaded anisometric contractions (concentric and eccentric phases) and isometric 9  contractions suggested task specific differences of greater MU activity in anisometric contractions than isometric contractions (Andrew, 1985; Linnamo, Moritani, Nicol, & Komi, 2002; Moritani, Muramatsu, & Muro, 1988).  This difference in MU activity is also evident at the level of the whole muscle. For example, electromyography (EMG) was greater in the anisometric contraction and the recruitment threshold was lower compared to the isometric contractions (Theeuwen, Gielen, & Miller, 1994). MU discharge rate also differed between these two types of contractions. The anisometric contractions have higher discharge rates than the isometric contractions (Harwood, Davidson, & Rice, 2010; Tax, Denier van der Gon, Gielen, & van den Temple, 1989). Finally, recruitment threshold is lower in anisometric contractions than isometric contractions (Table 1). This suggests that the net synaptic input onto the motor neuron pool differs between isometric and anisometric contractions and offers further evidence for the concept of task specificity (Enoka, 1995).  Table 1: Generalization of differences in MU activity between isometric and anisometric contractions  Isometric Anisometric MU Recruitment Threshold Higher Lower MU Discharge Rate Lower Higher  Many functional tasks necessary for daily living (drinking from a cup, pouring a glass of water from a jug, etc) contain both the eccentric and concentric phases of anisometric muscle contractions. Thus, further to the differences between isometric and anisometric contractions there may be additional differences within anisometric contractions between the two phases of the movement. Two reviews have extensively evaluated the control strategies for eccentric and concentric contractions (Duchateau & 10  Baudry, 2013; Enoka, 1996). It remains unclear whether the MU recruitment threshold differs between eccentric and concentric contractions as studies evaluating differences at high contraction velocities reported that high-threshold units were preferentially activated in eccentric contractions compared with concentric contractions (Nardone, Romano, & Schieppati, 1989). However, more recent studies have not reported these same differences in recruitment during slower contractions (Bawa & Jones, 1999; Laidlaw, Bilodeau, & Enoka, 2000; Sogaard, Christensen, Jensen, Finsen, & Sjogaard, 1996; Stotz & Bawa, 2001) and instead recruitment occurs similar to concentric contractions. MU discharge rate, on the other hand, is consistently reported as differing between eccentric and concentric contractions. Discharge rate is lower during eccentric contractions compared to concentric contractions (Del Valle & Thomas, 2006; Laidlaw et al, 2000; Semmler, Kornatz, Dinenno, Zhou, & Enoka, 2002; Sogaard et al, 1996; Stotz & Bawa, 2001; Tax et al, 1989). Duchateau & Baudry (2013) state that these results suggest rate coding is controlled differently between these two contraction types. Fang, Siemionow, Sahgal, Xiong & Yue (2001) showed that this unique strategy occurs because the brain plans and processes eccentric contractions in a unique manner to concentric contractions. EEG derived movement-related cortical potentials (both positive and negative) were higher in eccentric contractions than concentric contractions. The higher negative potential suggests that more cortical planning is required for eccentric contractions and the higher positive potential indicates that sensory feedback is used to a greater degree for eccentric contractions (Fang et al, 2001). Overall, if differences occur within anisometric contractions between eccentric and concentric aspects it is likely that unique activation strategies will also exist between functional tasks and anisometric contractions. As most functional tasks encompass both the eccentric and concentric aspects of muscle contraction, MU activity during all phases of a functional task must be considered.   11  No published studies to date have examined MU activity during a functional task. During a pilot MU experiment when a subject drank from a cup MU patterns were observed to differ between this movement and a controlled shortening contraction (Figure 2). Within the functional task MUs were recruited earlier and both the discharge rate and discharge rate variability were higher relative to the control shortening task. This pilot work, offers further evidence of task specific activation patterns. There is also evidence to suggest that with a muscle there are selective compartments activated independently of other regions of the muscle in response to a given task (Brown, Edwards, & Jakobi, 2010; Harwood, Edwards, & Jakobi, 2008). For example, ter Haar Romeny and colleagues (1984) found that motor units in different areas of the LH of the biceps brachii were selectively activated depending on the task that was being performed (lateral MUs for flexion but medial MUs for supination). Furthermore, these groups of MU may have specific central connections and recruitment patterns specialized for goal-directed tasks (Hoffer et al, 1987). Thus, it is hypothesized that MU activity will be greater (earlier MU recruitment and higher discharge rate) in functional tasks than simple, anisometric contractions. Furthermore, the task with the highest MU discharge rates will be most steady. 12   Figure 2: Motor unit activity in an anisometric contraction (A) and functional task (B). The functional task has earlier recruitment of MUs, more MUs overall are recruited, and the discharge rate is more variable compared to the anisometric contraction. This provides a clear visual indication that MU activity is different in functional tasks than anisometric contractions. sec, seconds; SH, short head of the biceps brachii; mV, millivolts.  1.4 Control of Muscle Contractions Steadiness is the ability to maintain a muscle contraction at a given target or force and offers a quantitative measure of functional ability. Steadiness varies with many different conditions including position (Figure 3), age, intensity of contraction and sex (Figure 4) (Brown et al, 2010; Harwood et al, 2008; Tracey & Enoka, 2002). When the forearm is in the pronated position, steadiness is significantly less than when the forearm is in the neutral or supinated position (Figure 3). Further, older adults are significantly less steady than younger adults (Harwood et al, 2008) and males are steadier than females (Brown et al, 2010) (Figure 4). The underlying cause for force steadiness differing across 13  positions, between sexes and with age remains uncertain. Muscle strength contributes to these position, sex- and age-related differences in steadiness (Brown et al, 2010); however, MU activity and MU discharge rate variability may also play a role (Graves et al, 2000; Marmon, Pascoe, Schwartz, & Enoka , 2011). In addition, steadiness may vary depending on the task being performed.  (Unpublished data from Neuromuscular lab, UBCO)  Figure 3: Positional differences in force steadiness of the elbow flexors. In the pronated forearm position subjects are less steady compared to the neutral forearm position across different submaximal force levels for isometric contractions. Subjects were assessed at 2.5, 10, 17.5 and 25% of  MVC. CV, coefficient of variation which is inversely related to force steadiness (the higher the number the less steady the contraction); MVC, maximal voluntary contraction. *Pronated significantly less steady than neutral position (p<0.001)  14   (Obtained from Brown et al, 2010)  (Appendix A) Figure 4: Sex differences in elbow flexor force steadiness across submaximal force levels.  Force steadiness is represented as the coefficient of variation which is inversely related to force steadiness. Men were significantly steadier than women across all submaximal force levels. CV, coefficient of variation; MVC, maximal voluntary contraction. *Women significantly less steady than men (P<0.05)   Steadiness is a greater predictor of functional performance than strength (Marmon et al, 2011; Seynnes et al, 2005); however, no studies to date have examined MU activity and steadiness in functional tasks relative to anisometric or isometric contractions.  In anisometric and isometric contractions steadiness declines with advancing age and this effect is greater in females relative to males (Brown et al, 2010, Harwood et al. 2010). Greater age-related declines in functional ability in females relative to males is well established and is often attributed to alterations within the musculoskeletal system relative to muscle size and quality (Ganesh, Fried, Taylor, Pieper, & Hoenig, 2011; Harwood et al. 2010); yet, the contribution of the nervous system remains less clear. The neuromuscular system and MU activity is traditionally studied less frequently in females than males, yet they experience greater and earlier decline of functional ability. It is 15  important to determine whether differences in MU activity are evident between functional tasks and lab-based anisometric contractions in this population to better understand the earlier functional decline females? experience. Teasing out the differences between functional tasks and anisometric contractions will help in understanding the underlying cause of functional change, and facilitate the design of training/rehabilitation programs to help females maintain functional independence.  1.6 Summary of Literature To date, no studies have examined MU activity in purposeful, functional tasks. It is well established that recruitment of MUs is lower in anisometric contractions compared with isometric contractions (Harwood et al, 2010; Ivanova, Garland, & Miller, 1997; Linnamo et al, 2002; Tax et al, 1989; Theeuwen et al, 1994). The lower recruitment threshold suggests that MUs are activated at a lower force level in anisometric contractions compared with isometric. Recruitment threshold of MUs is generally believed to follow Henneman?s size principal (1957); however, this fundamental tenet is now seen as a more integrative approach to neuromuscular activation. Hodson-Tole and Wakeling (2008) suggest that mechanics, sensory feedback (Basmajian, 1963) and descending drive all influence the recruitment of MUs and thus differences would occur between functional tasks and anisometric contractions as a consequence of these contributing variables that differ between conditions.  It is also well established that MU discharge rates are higher in anisometric contractions compared with isometric contractions. (Harwood et al, 2010; Ivanova et al, 1997; Linnamo et al, 2002; Tax et al, 1989; Theeuwen et al, 1994), as discharge rate increases linearly with both velocity and intensity of contractions (Harwood et al, 2010). Further, it has recently become clear that discharge rate does differ between eccentric and 16  concentric phases of anisometric contractions. Discharge rate is lower during the eccentric phase than the concentric phase (Duchateau and Baudry, 2013). Both MU recruitment and discharge rate are likely to further differ in functional movement as the complexity of contraction continues to increase from isometric to anisometric to functional tasks. Because steadiness is a good predictor of functional performance (Marmon et al, 2011) it is likely that steadiness will also differ between these three contraction types. As functional tasks require the greatest amount of control to properly execute it is plausible to assume that the functional tasks will produce the steadiest contractions. Females are less steady than males and experience functional decline at an earlier age. Thus, it is important to understand the spinal control of functional tasks, particularly in females, as performance of functional tasks is essential to daily living. Differences in spinal control during functional movement will highlight that these contractions are mechanistically different from laboratory based anisometric and isometric conditions. Increased motor unit activity during these functional movements will indicate that spinal control is not only task specific, but sensitive to goal directed outcomes that involve higher level of processing.    17  Chapter 2: Aims and Hypotheses 2.1 Purpose The purpose of this study was to evaluate MU activity and steadiness between controlled lab-based anisometric contractions and functional tasks in young women. Further, specific differences in the eccentric and concentric aspects of the contractions were examined.  2.2 Aims a. To determine whether the addition of a specific purpose, namely lifting a waterbottle and drinking, will lower MU recruitment thresholds. b. To determine whether the addition of a task specific purpose will change MU discharge rate c. To compare the concentric and eccentric phases of the contractions and determine whether the MU discharge rates which are reported to be lower in the eccentric phase remains consistent for anisometric and functional tasks.  d. To evaluate steadiness between the contraction types. 2.3 Hypotheses a. MU recruitment threshold will be lower in the water drinking functional task compared with anisometric contractions which will be lower compared with isometric contractions. 18  b. MU discharge rate will be higher in the water drinking functional task compared with anisometric contractions which will be higher compared with isometric contractions. c. The eccentric (lowering) phase of all contractions will maintain a lower discharge rate regardless of the addition of a specific purpose. d. The water drinking functional task will produce the steadiest contraction.  19  Chapter 3: Methods 3.1 Participants Thirteen healthy female subjects aged 18 ? 30 years were recruited for this study. Subjects were excluded it they had current or previous neuromuscular disease, were male, were under the age of 18 or over the age of 30 years, or participated in high level of athletic training (ie elite athletes or varsity athletes). Further, participants were screened for skilled task training in activities that require fine motor control such as musicians and artists. Persons practiced in fine motor control were excluded, as training alters MU activation strategies (Semmler & Nordstrom, 1998). All subjects were tested during the follicular phase (days 1-13) of their menstrual cycle and were currently taking oral contraceptives to control for hormone levels.   Subjects were asked to refrain from caffeine 12 hours prior to testing and from any physical activity on the day of testing. Informed and written consent was obtained from all participants prior to participation in the study. All procedures were approved according to the Clinical Research Ethics Board at the University of British Columbia and conformed to the Declaration of Helsinki (Appendix B). 3.2 Experimental Set-Up Muscle activity was recorded from the SH and LH of the biceps brachii, triceps brachii, and brachioradialis. Intramuscular EMG was recorded from the SH and LH of the biceps brachii to assess MU recruitment and discharge rates. Acceleration was recorded at the subject?s wrist. Subjects were seated in a custom-made chair and visual feedback was provided on 19-in computer screen monitor (1280 x 1024 resolution) located 1 m in front of 20  The screen was located slightly off centre, in front of the subject?s right arm, to that both the screen and the waterbottle were in the line of vision for all phases of for lifting and lowering the waterbottle as well as drinking through the straw. The distance between the subject?s eyes and the screen was measured as was the angle between the subject?s eyes and the centre of the computer monitor to ensure that subjects were receiving the same amount of visual feedback. The range of motion required to move the waterbottle from the starting position to place the straw in subject?s mouth was measured to ensure all contractions were performed over the distance ( Figure 5).  Bipolar surface electrodes (4mm Ag/AgCl) were placed over the muscle belly of the SH, LH, brachioradialis and wrist flexors with an inter-electrode distance of approximately 1 centimetre. Reference electrodes for the SH and LH of the biceps brachii were placed over the acromion process of the scapula. The lateral epicondyle was used as the bony prominence for reference of the brachioradialis and the medial epicondyle for the wrist flexors (Figure 6). The skin of the arm and forearm was exfoliated with low friction cleansing pads and 70% isopropyl alcohol swabs to allow better conductivity for the electrodes.  The signal from the surface EMG was sampled at 1024 Hz (1401, CED, Cambridge, England) amplified (x 500) with an isolated bioamplifier (Coulbourn Electronic, Allentown, Pennsylvania), band-pass filtered (8Hz ? 500Hz) (Coulbourn, Allentown, Pennsylvania) and converted from analog to digital format (CED, Cambridge, England).  An accelerometer (V94-41 Acceleration 10G, Coulbourn, Allentown, Pennsylvania) was taped to the subject?s wrist. The recording from this device was displayed in real-time on the computer screen monitor to provide the subject with visual 21  feedback of the movements. Acceleration data was also recorded to allow calculation of steadiness during the contractions.   22     Figure 5: Experimental set-up Representative diagram of the experimental set-up. Subjects sat in a custom-made chair so that their hips and knees were at 90?. A stool was provided for their feet to rest on. A table was located above their legs and the waterbottle rested on this prior to the contraction. Visual feedback was displayed on a computer monitor that was 1m in front of the subject. The distance between each subjects eyes and the angle from the centre of the computer screen to the eyes was measured to ensure all subjects were receiving similar visual feedback. The distance between the initial position of the waterbottle on the table and the position where the straw reached the subjects mouth (showing in the dotted lines) was measured with a goniometer to ensure all contractions were performed through the same range of motion.       23   Figure 6: EMG and MU set-up Representative picture of the EMG and MU set-up. Not all surface electrodes and fine wires are visible. The surface electrodes recording the LH of the biceps brachii are visible. All other electrode pairs were attached in a similar fashion. Part of the electrodes on the SH of the biceps brachii are evident on the medial aspect of the arm. The triceps brachii electrodes are located on the posterior aspect of the arm and cannot be seen in this picture. The electrodes located under the mesh netting, inferior to the elbow joint are recording brachioradialis EMG. The mesh netting was used for additional securement of the wires during the movement which assisted in reducing movement artefact in the signals. Ground electrodes are apparent on the elbow, shoulder, and clavicle. The two clips located to the right of the preamplifier (black box) were used to hook the fine wire electrodes into the preamplifier. The fine wire is inserted into the LH of the biceps brachii between the two surface electrodes. A similar set-up was used with clips and amplifiers for the fine wires of the SH.   Custom-made fine wire electrodes were used to record single MU activity. Three wires (25-50 ?m diameter, California Fine Wire, Grover Beach, California) of approximately 25 cm in length were aligned and the ends were glued together. These fine 24  wire units were threaded through a one-inch long 25 gauge hypodermic needle. The wires and hypodermic needles were then autoclaved for sterilization. One hypodermic needle was inserted into the muscle belly of the SH of the biceps brachii and a second one into the LH of the biceps brachii (Figure 6). The wire was placed approximately 2.5 centimetres into the muscle; pending the size of each individual muscle. Immediately after insertion the hypodermic needle was withdrawn and the wires remained in-place for the duration of the experiment. The ends of the wires not inserted into the muscle were separated. The coating of the ends of the wires was burned off and scraped with sandpaper to enhance contact and reduce impedance. These were attached to a custom-made pre-amplifier that amplified the signal 10 times (University of Windsor). If a clear signal was not obtained the remaining third wire was used instead of one of the original two wires. A ground surface electrode was placed over the medial end of the clavicle for the SH, and on the lateral end of the clavicle for the LH.  The MU signal was sampled at a rate of 16 666 Hz, amplified (100-1000 times) and band-pass filtered (8Hz ? 1kHz) (Coulbourn, Allentown, Pennsylvania).  Intramuscular EMG was converted from analog to digital format by a 16-bit A/D converter (1401 plus, CED, Cambridge, England).   3.3 Experimental Protocol  Participants attended the lab on one occasion for this study. Subjects completed the Edinburgh handedness questionnaire (Oldfield, 1971) as well as a background information questionnaire regarding hobbies, physical activities and previous employment (Appendix C).  Subjects performed three isometric maximal voluntary contractions (MVCs) of each of the biceps brachii, triceps brachii and brachioradialis so that all force data could be normalized. MVCs were held for 5-seconds each and approximately 2 minutes of rest was given between each trial. If the MVCs were not consistent additional 25  attempts were performed to ensure subjects reached their true maximal effort. Strong verbal encouragement was given during the MVC contractions. The highest MVC was used as the subject?s maximal effort. Subjects then performed the 4 experimental contractions in a randomized order with approximately 2 minutes of rest between each contraction. Three trials of each condition were conducted resulting in a total of 12 experimental contractions. The functional task was a waterbottle drinking task. The 3 other tasks (waterbottle lift, anisometric and isometric contractions) were matched to this contraction. All tasks were performed with the wrist in the neutral forearm position and were matched for shape, weight, velocity, acceleration, and range of motion.   The waterbottle drinking task consisted of lifting a waterbottle and the attached straw (800 grams) off of a table and holding this initial position for 5 seconds. The bottle was then slowly raised towards the subjects? mouth over ten seconds. A second hold was performed in which the subject held the bottle in this lifted position for 5 seconds. In this task the subject took a sip of water through the straw. The bottle was then lowered back towards the table over 10 seconds and then a final 5 second hold was executed just above the table surface. The entire contraction took 35 seconds and subjects were provided with visual feedback of acceleration throughout the entire task (Figure 7).  The visual feedback displayed real-time tracings of the acceleration output. Horizontal lines were set to display the maximum and minimum acceleration and subjects were instructed to keep acceleration within this limited range.  Vertical cursors were used to display when a movement started or changed. Six vertical cursors were evident on the screen to indicate the individual phases of the task: pick up the bottle and hold, lifting, holding near the face, lowering, holding just above the table, and release of the water bottle (Figure 7). Verbal feedback was also provided to indicate the initiation and cessation of the task.  26   The second task was a waterbottle lift task. In this task an identical movement to the waterbottle drink contraction was performed; however, during the holding phase near the face no sip of water was taken. Third, a simple, anisometric control contraction was also performed. For this contraction a waterbottle without a straw was weighted with lead sinkers to equal the waterbottle drink and lift task (800 grams). The weights were equally distributed and fastened to the inside of the bottle.  Hand position, timing of the movement and range of motion were matched to the drinking and lifting tasks, but the subjects were not required to drink. Instead a 5 second hold was performed at the end of the same range of motion of the prior two (waterbottle drink and waterbottle lift) tasks.    The last of the four contractions executed was a basic isometric contraction in which the subject pulled up against a resistance while their arm was immobile. The target force was matched to the other tasks and displayed on the computer monitor. Visual feedback of force output was displayed. This contraction was held for a 35 second duration to match the time of the other tasks. Isometric contractions were performed as a second control contraction in order to confirm the results currently reported in the literature between isometric and anisometric contractions and offer a further comparative for the functional tasks. 3.4 Data Analysis Data analysis was performed using custom-scripts for Spike 2 (CED, Cambridge, England). Surface EMG signals were rectified and integrated (Figure 8). Integrated surface EMG is calculated as the area under the rectified EMG signal. Averages for 0.5 second windows of the integrated EMG signal were obtained for each phase of the contraction (1st hold, lift, 2nd hold, lower, 3rd hold). The 3 hold phases (1st hold, 2nd hold, 3rd hold) were each 5 seconds in duration. The first two seconds and the last second 27   Figure 7: Representative visual feedback.  The tracing in the middle of the figure is the ?live? feedback representation of acceleration. The two horizontal lines are the maximum and minimum acceptable accelerations with the target being zero acceleration achieved by keeping the live tracing flat and in the middle of the two lines. The vertical lines indicate when a movement starts or changes. At the first line which is labelled ?HOLD? the subject held the object off the table. At the LIFT line the subject slowly raised the bottle to the mouth. At the 2nd HOLD line the subject held the position at the top of the range of motion. The LOWER line indicated the object was to be lowered. The final HOLD line indicates the last phase just above the table and the RELEASE line is when the contraction ends. The horizontal axis displays the time and the vertical axis the acceleration. This feedback was given for the waterbottle functional task as well as the anisometric matched contraction.  were excluded to account for movement into and out of the phase to ensure that the subject was holding the contraction, thus the analysis was done for 2 seconds at a stable joint angle. The two movement phases (lift, lower) were 10 seconds in duration. The first second was excluded as subjects were accelerating to begin the movement. The next 4 seconds were analyzed while the subject was moving at a constant velocity with no acceleration. The final 5 seconds were excluded as some subjects had a smaller range of motion and reached their mouth in less than 10 seconds. This ensured that the part of the 28  integrated EMG signal that was analyzed represented the movement phase. Surface EMG from each phase of all contractions was divided by the maximal EMG obtained during the MVC contractions. This allowed relative comparisons to be made between isometric, anisometric and functional contractions and between the 4 muscle groups.   Steadiness was calculated as the coefficient of variation of the absolute acceleration. Coefficient of variation is inversely related to steadiness, therefore the higher the coefficient of variation the lower the force steadiness. The absolute level of acceleration was used because the target acceleration for these contractions was established to be zero. Thus, averaging the deviations resulted in signal cancellation between the negative and positive phases giving a falsely low variation of acceleration. By taking the absolute values (positive number) the calculated deviation was more representative of the variation in acceleration.   Indwelling EMG recordings were high-pass filtered and the slope calculated to make tracings clear for MU analysis. MU recordings were analyzed using a template matching algorithm which allowed MUs to be identified based on waveform shape and size. Templates were created and overlaying of subsequent action potentials allowed coding to be completed so that all action potentials belonging to the same MU train were assessed within one group (Figure 9). Visual inspection was then conducted to ensure every single MU action potential was properly coded. MUs were analyzed if there was a minimum of 6 discharges. Importantly, MUs were tracked between all contraction types (isometric, anisometric, waterbottle lift, and waterbottle drink). MUs present in all 4 contraction types were coded the same so that comparisons between contractions could be made for specific MUs. However, fewer action potentials were evident in the isometric contraction thus MUs were also tracked if they were only present in the anisometric and functional contractions. Any MUs only appearing in one contraction were analyzed and 29  coded individually for separate analysis of additionally recruited MUs. Sixty-eight MUs were analyzed and tracked throughout the contraction types in the SH of the biceps brachii and 53 in the LH of the biceps brachii.     Figure 8: Representative surface EMG data analysis.  Panel a (bottom tracing) shows the interference pattern of the surface EMG recording from the SH of the biceps brachii. Panel b (second tracing) is the rectified EMG output for the same task for the entire contraction duration. Panel c shows the integrated EMG output for the 5 phases of the contraction. All EMG tracings are shown in millivolts. SH, short head of the biceps brachii; v, volts; iEMG, integrated EMG; sec, seconds.  30    Figure 9: Representative motor unit analysis   Motor unit analysis was performed using scripts in Spike 2. An example analysis is shown including the raw intramuscular EMG recording, filtered intramuscular EMG  and MUs analyzed from this recording. The bottom tracing shows the raw SH intramuscular EMG recording in mV. This recording was then high-pass filtered using an IIR filter in Spike 2. The slope of this tracing was then obtained to make MUs as clear as possible for analysis. All tracings were filtered in an identical way so that all MUs were still comparable between the 4 contraction types. The filtered tracing is shown above the raw intramuscular EMG tracing labelled as SH (IIR). The three tracings above in the main panel of the figure show the three different MUs that were analyzed. MUs were identified using a template matching alogrithm which is shown in insert A). The top half of this box shows the MU that is currently being analyzed. There are 6 boxes in the bottom half of this template matching alogrithm, three of which are filled with three different MUs numbered 1, 2 and 3. These three templates were used to identify the MUs shown in the top three tracings of the main panel labelled MU1, MU2, and MU3. Visual inspection was then employed to ensure all MUs were coded correctly. Panel B shows enhanced magnified version of the three different MUs are identified and correspond in colour and number to panel B.  SH, short head; mV, millivolts; MU, motor Unit.   31  Discharge rate (Hz), discharge rate variability (SD of discharge rate), interspike intervals and the SD of interspike intervals were calculated. Recruitment threshold was calculated as the time of onset of each specific MU train as all contractions were time-locked so recruitment could be analyzed at the time of first discharge.  3.5 Statistical Analysis  The normality of all data was evaluated. All normally distributed data is presented in text as means ? SD; all non-normally distributed data is presented as median ? interquartile range. If not specified the data is normally distributed and the mean ? SD is reported. All data in graphs is presented as mean ? standard error of the mean (SEM). One-sample t-tests were conducted to evaluate differences in subject characteristics.   A 4 (muscle group - SH and LH of the biceps brachii, triceps brachii and brachioradialis) x 5 (phase of contraction - 1st hold, lift, 2nd hold, lower, 3rd hold) repeated measures ANOVA was used to evaluate differences in integrated EMG between the 4 contraction types (isometric, anisometric, waterbottle lift, waterbottle drink).  A repeated measures ANOVA was also used to evaluate differences in acceleration steadiness across the 5 phases of the contraction between the three dynamic contraction types (anisometric, waterbottle lift and waterbottle drink).   A 2 (muscle group - SH and LH of the biceps brachii) x 5 (phase of contraction) repeated measures ANOVA was used to evaluated differences in MU discharge rate and MU discharge rate variability between the 4 contraction types (isometric, anisometric, waterbottle lift and waterbottle drink).  A repeated measures ANOVA was used to evaluate recruitment time of MUs between the SH and LH and the 4 different contraction types. Tukey's post hoc analysis was performed for all significant interactions. All 32  statistical procedures were performed using SPSS (v. 19, Chicago, IL). An ? level of p?0.05 was used for statistical significance. Chapter 4: Results 4.1 Subjects  Thirteen female subjects (22.5 ? 2.9 years; 59.2 ? 7.0 kg; 166.5 ? 7.8 cm) were recruited for this study. Measurements of the distance between the subject?s eye and the visual feedback computer screen monitor were taken prior to testing. The subjects were 125.0 ? 2.1 cm away from the screen. The angle was also measured using a goniometer between the subject?s eye and the centre of the computer monitor and all subjects looked slightly downwards at the computer monitor (-3.6 ? 2.4?). The range of motion at the subjects elbow was taken to determine the degree to which the subject moved the waterbottle or weight (38.5 ? 4.3?). Maximal strength measurements were obtained for elbow flexion and elbow extension. Subjects were significantly stronger for elbow flexion compared with elbow extension (p=0.001) (Table 2). Table 2: Maximal voluntary contraction strength Subject # Elbow flexion MVC  (N) Elbow Extension MVC (N) Average 145.127* 107.394 SD 30.720 20.176 Subject results are presented as the highest value of three trials. *, biceps brachii strength was significantly stronger than triceps brachii strength (p=0.001). N, newtons; SD, standard deviation.   4.2 Surface EMG  The repeated measures ANOVA of integrated surface EMG did not result in a 3 way contraction x contraction phase x muscle group interaction (p>0.05) but resulted in a 33  significant contraction x phase interaction (p<0.001) and a significant contraction x muscle group interaction (p<0.001). In the LH of the biceps brachii (p=0.03) the isometric contraction had significantly lower integrated EMG than the other three contractions (anisometric, waterbottle lift, waterbottle drink) in the 1st hold (p<0.01), lift (p<0.001), 2nd hold (p<0.01) and lower (p<0.05) phases of the contractions. However there were no significant differences in the 3rd hold phase of the contractions (Figure 10). In the SH of the biceps brachii the isometric contraction had significantly lower integrated EMG than the other three contractions (anisometric, waterbottle lift, waterbottle drink) in the 1st hold (p<0.01), lift (p<0.001), 2nd hold (p<0.001), and lower (p<0.001) phases of the contractions. In the 3rd hold phase the isometric contraction was only significantly lower than the waterbottle drink contraction (p<0.05). Additionally, during the lower phase the drink contraction had significantly lower integrated EMG than the anisometric and waterbottle lift contractions (p=0.009) (Figure 10).  There was no significant contraction x phase interaction in the triceps brachii or brachioradialis muscles (p>0.05). No main effects were observed for the triceps brachii; however, a main effect for contraction was seen in the brachioradialis (p<0.001). The isometric contraction had significantly lower integrated EMG than the other three contraction types (p<0.001). Additionally the anisometric contraction had significantly lower integrated EMG than the waterbottle lift and waterbottle drink contractions (p<0.01) (Figure 11).     34   Figure 10: EMG activity of the long (A) and short (B) head of the biceps brachii during the 4 different contractions. Muscle activity is represented as the mean integrated EMG as a percentage of the subject's maximal EMG. All bars represent the average of all subjects. a, significantly different than all other contraction types. MVC, maximal voluntary contraction; aniso, anisometric contraction; Wb Lift, waterbottle lift contraction; Wb Drink, waterbottle drink contraction; Iso, isometric contraction.  4.3 Steadiness  The repeated measures ANOVA of the coefficient of variation of acceleration (steadiness) resulted in a significant contraction type x phase of contraction interaction. Pairwise comparisons showed that during the 1st, 2nd and 3rd hold phases of the contractions (anisometric, waterbottle lift, waterbottle drink) there were no significant differences. The lift phase of the anisometric contraction was significantly steadier than the waterbottle drink contraction (p=0.02); however, there were no differences between the anisometric and waterbottle lift contraction or the waterbottle lift and waterbottle drink contraction. During the lower phase the anisometric contraction was significantly steadier than the waterbottle lift (p=0.016) and the waterbottle drink (p<0.001) 35  contractions. The waterbottle lift contraction was significantly steadier than the waterbottle drink contraction (p=0.03) (Figure 12).     Figure 11: EMG activity of the brachioradialis during the four different contractions. Muscle activity is represented as the mean integrated EMG as a percentage of the subject's maximal EMG. All bars represent the average of all subjects across all phases of the contraction type. a, significantly different than all other contraction types. MVC, maximal voluntary contraction; aniso, anisometric contraction; Wb Lift, waterbottle lift contraction; Wb Drink, waterbottle drink contraction; Iso, isometric contraction.   4.4 MU Characteristics  The repeated measures ANOVA for discharge rate did not show a 3 way contraction x contraction phase x muscle group interaction. There was a significant contraction x contraction phase interaction (p<0.001) and a significant contraction x muscle group interaction (p=0.001). In the LH of the biceps brachii, during the 1st hold and lower phases there was no difference (p>0.05); however, all other phases differed (p<0.05). This was caused by the waterbottle drink contraction having a significantly higher discharge rate than the other three contractions (anisometric, waterbottle lift, and  36   Figure 12: Steadiness during the 5 phases of the dynamic contractions. Steadiness is represented as the coefficient of variation (CV) of acceleration which is inversely related to steadiness. Therefore the higher the CV the less steady the contraction. Steadiness did not differ between the holding phases across the three contractions. During the lift phase the waterbottle drink contraction was significantly less steady than the anisometric contraction. In the lowering phase the waterbottle drink contraction was the least steady followed by the waterbottle lift. The anisometric contraction was the steadiest in this phase. Because steadiness was calculated using the absolute values of acceleration this could not be directly compared to the isometric force steadiness. Therefore the isometric contraction is omitted from this figure. a, significantly different than all other contraction types; c, significantly different than anisometric. CV, coefficient of variation; Aniso, anisometric contraction; Wb lift, waterbottle lift contraction; Wb drink, waterbottle drink contraction.  isometric) in the lift phase (p<0.01). Additionally the waterbottle lift contraction had a significantly higher discharge rate than the isometric contraction (p<0.05). In the 2nd hold phase the waterbottle drink contraction had a significantly higher DR than the isometric contraction (p<0.05). Finally, during the 3rd hold phase the isometric had significantly higher DR than the other three contraction types (p<0.05) (Figure 13).   In the SH of the biceps brachii the 1st hold phase of the isometric contraction had a significantly lower discharge rate than the waterbottle lift and waterbottle drink contraction (p<0.05). During the lift phase all contractions were significantly different 37  from one another (p<0.05) except the anisometric and waterbottle lift contraction which were not significantly different (p>0.05). The waterbottle drink contraction had a higher discharge rate than all other contractions and the isometric contraction had a lower discharge rate than all other contractions (p<0.05).  During the 2nd hold and lower phase the waterbottle drink contraction had a significantly higher discharge rat than the anisometric and isometric contraction (p<0.05) (Figure 13).  Figure 13: Motor unit discharge rate of the long (A) and short (B) head of the biceps brachii during the 4 different contractions Motor units were tracked throughout the 5 phases of the contraction and between the 3 different contractions (anisometric, waterbottle lift, waterbottle drink, and isometric). The waterbottle drink contraction had a significantly higher discharge rate than the other three contraction types in the lifting phase in both the SH and LH of the biceps brachii. In addition the waterbottle drink contraction had a significantly higher discharge rate than the isometric contraction in the 2nd hold phase in the LH and in the 1st hold, 2nd hold and lower phases in the SH of the biceps brachii. The anisometric and waterbottle lift contraction were similar across all phases and both heads. a, significantly different than all other contraction types; b, significantly different than isometric; c, significantly different than anisometric. Aniso, anisometric; WB lift, waterbottle lift; WB drink, waterbottle drink; Iso, isometric; Hz, hertz.   38  The repeated measures ANOVA for discharge rate variability did not reveal any interactions; however, there was a main effect for contraction (p<0.001). Post-hoc analysis revealed that the waterbottle drink contraction had a significantly higher discharge rate variability than the other three contraction types (anisometric, waterbottle lift, isometric) (p<0.05). Additionally the isometric contraction had a significantly lower discharge rate variability than the other three contraction types (p<0.001). There were no significant differences between the anisometric and waterbottle lift contraction (p>0.05) (Figure 14).   Figure 14: Motor unit discharge rate variability in the 4 different contractions. Discharge rate variability was significantly higher in the waterbottle drink contraction than the other three contraction types (anisometric, waterbottle lift and isometric). The isometric contraction had a significantly lower discharge rate than the other three contraction types. The anisometric and waterbottle lift contraction were not significantly different. a, significantly different than all other contraction types. Aniso, anisometric; WB lift, waterbottle lift; WB drink, waterbottle drink; Iso, isometric; Hz, hertz.  39   The repeated measures ANOVA for recruitment time did not result in a significant muscle x contraction interaction or a significant main effect for contraction (p>0.05) (Figure 15).  Figure 15: Motor unit recruitment time between the 4 contraction types. MU recruitment time was obtained for all tracked motor units. Recruitment time was considered to be the point when the MU first turned on and discharged consistently 6 or more times. The contraction started at 20.00 seconds therefore the earliest possible recruitment time was 20.00 seconds. There were no significant differences between any of the contraction types for recruitment time. Aniso, anisometric; WB lift, waterbottle lift; WB drink, waterbottle drink; Iso, isometric; sec, seconds.  Chapter 5: Discussion  This is the first study to measure MU discharge rates and recruitment in a functional task and compare this activity to isometric and anisometric contractions in order to understand the production of steady movements. The main findings from this study were: 1) isometric contractions performed at the same workload require less muscle activity (measured via integrated EMG) than anisometric contractions and functional tasks; 2) during the movement phases of the contractions, the functional task was 40  significantly less steady than the anisometric contraction; 3) the waterbottle drink contraction had a significantly higher discharge rate than the other contraction types during the lift phases; 4) the waterbottle drink contraction had the highest discharge rate variability and the isometric contraction had the lowest; 5) recruitment time did not differ between the 4 contraction types. Overall, the intent to drink (functional task) influenced spinal integration, as measured in MU output and this change in the peripheral nervous system effected task control.   In this study surface EMG of the SH and LH of the biceps brachii, triceps brachii and brachioradialis were measured.  All contractions that were performed were completed at the same workload, thus surface EMG was expected to be similar between the four contractions. However, in the SH and LH of the biceps brachii the isometric contraction had significantly lower integrated EMG activity than the other three contraction types (Figure 10). This is due to the addition of movement in the other contraction types (Theeuwen et al, 1994). Although the relative load was the same, in the movement tasks the load had to be moved against gravity whereas in the isometric contraction the arm remained stable. The three dynamic contractions were not significantly different in terms of integrated EMG. This indicated that the net drive to the muscle was similar between the contraction types.    This study highlighted that execution of a functional tasks requires unique spinal control, measured through the evaluation of MU activity, specifically quantification of the rate coding strategy. This study is strengthened by tracking MUs across all 4 contraction types. Therefore, these results are a compilation of specific differences in the same MU across the conditions. Discharge rate was highest in the waterbottle drink contraction compared to the other three contraction types. The only difference between the waterbottle lift and waterbottle drink contraction was the addition of a sip of water during 41  the 2nd hold phase. Therefore the 1st hold and lift phases were identical yet the discharge rate was significantly higher in the lift phase in the waterbottle drink contraction. On the other hand, the waterbottle lift contraction and lab-based anisometric control contraction were not significantly different in terms of discharge rate. Thus, taking a drink of water, making the task a true functional task, was enough to influence how the task was controlled.   The higher discharge rate in the waterbottle drink contraction must therefore be occurring to assist in controlling the complexity of the task. It is well established that DR is higher in anisometric contractions compared to isometric contractions (Altenberg, Ruiter, Verdlijk, Mechelen, & de Haan, 2009; Kallio et al, 2013). These differences are confirmed by this study as the isometric contraction had the lowest discharge rate. It appears that these differences in rate coding strategy are further extended as task complexity is augmented.  In addition to discharge rate, recruitment of motor units can also play a role in controlling muscle contractions (Kukulka & Carmann, 1981). Recruitment time did not differ between the contraction types in this study. This suggests that recruitment may occur based on the load of the contraction whereas, rate coding likely involves a level of higher order processing that accounts for complexity of the task. Recruitment time was similar in the isometric contraction to the three dynamic contractions. This contradicts previous findings that isometric contractions have a higher recruitment threshold than anisometric contractions (Linnamo et al, 2002). However, it should be noted that in this study in order to achieve the desired force level to match the dynamic contractions subjects were given a 7 second ramp time to reach the force level. This occurred as in the dynamic contractions; as soon as the waterbottle was lifted the full load was maintained in a constant position. Thus, the full load of the water bottle was being used throughout the 42  isometric contraction, thus a slow ramp phase was used to ?match? conditions. This slow ramp may have masked some of the differences. However, what is important to note is that less MUs were activated during the isometric contraction compared to the other three contraction types. Thus, recruitment was still lower during the isometric contraction compared to the dynamic contractions, further indicating that spinal output to execute the task is less in this condition.    Steadiness is associated with discharge rate variability. The more variable the output of the spinal network the less steady the contraction. Typically, in isometric and anisometric contractions, a higher discharge rate is associated with lower discharge rate variability and this was observed in the water bottle lift. However, this was not evident in the functional drinking tasks. In the waterbottle drink contraction the discharge rate was higher as was the discharge rate variability resulting in a lower steadiness in this contraction. Davids, Bennet, & Newell (2006) state that as learning occurs in a task and experience in executing the movement increases the mechanical aspects of the system become less rigid. Instead, as people perform tasks they learn which features are invariant and which can vary and adapt to successfully perform the task in different environments (Davids et al, 2006). This could explain why the waterbottle drinking task was least steady. In order to successfully execute the task that subjects needed to direct the straw to their mouths. However, how steady the movement was wouldn't change the outcome (obtaining a sip of water) of the task. Meanwhile, during the anisometric contraction and waterbottle lift contraction, removal of the drink made the task less familiar. In these cases the subjects had to concentrate on carefully moving the waterbottle to the correct position, and ignoring the innate drive to ?drink?. Thus, the spinal output is heightened and MU variability would be less in the lift relative to the drink contraction.  43  This is an important finding as some contractions of daily life require steadiness to properly execute the task. For example, had the waterbottle been a mug of hot liquid it would be important to maintain a steady contraction in order to prevent spilling. This suggests that steadiness is not only influenced by the complexity of the task, but familiarity with the functional movement. This has implications for people wanting to maintain steadiness to complete tasks of daily living. Thus, it is important to determine ways in which functional tasks become steadier. A recent study by Marmon, Gould, & Enoka (2011) showed that practicing specific functional movements could improve steadiness in older adults.  In addition to the differences observed between the 4 contraction types, differences in the concentric (lift) and eccentric (lower) phases of the contractions were also observed. It is well established that concentric contractions require unique control strategies to eccentric contractions with concentric contractions having a higher discharge rate (Duchateau & Baudry, 2013; Enoka, 1996). Across the three dynamic contractions this held true in this study. The lift phase had a higher discharge rate than the lower phase (Figure 13). This is important to note as adding the functional aspect to the task does not influence the control strategies between concentric and eccentric phases. Overall this study was the first to highlight that functional tasks require unique control strategies to anisometric and isometric contractions. Recruitment does not control the more complex functional tasks; rather rate coding is the key aspect of regulating functional movement.  5.1 Limitations  This study evaluated an entirely novel concept of recording and quantifying MUs during functional tasks.  As this was a completely new experimental set-up and protocol 44  there were a few limitations that arose within this study that can be addressed by future research. The equipment used for this set-up only allowed recordings from 6 muscle groups (surface EMG of the SH and LH of the biceps brachii, triceps brachii and brachioradialis and intramuscular EMG of the SH and LH of the biceps brachii). If the subjects had pronated their forearm at all in order to place the straw into their mouth then brachialis activity would also need to be considered.  Current motor unit recording techniques make it difficult to anlayze MUs at high contraction velocities, particularly in this set up for functional movement. The movements had to be performed at a slow pace in order to obtain clear MU recordings; this may not have completely represented the movement time required to ?drink?. However, even at this slow pace, differences were still observed between the contraction types.   5.2 Future Research  This study highlights that with careful advancement of electrophysiology recordings, single MU activity can be quantified in functional movement. Data here underscores both the enormous potential, and the great need for extensive and future research in understanding functional movement in humans. Motor unit populations between muscles likely have unique and specific spinal control strategies that are directed to the tasks undertaken. This specificity might also be openly affected by the complexity of the task.  The drinking task investigated involves a flexion and extension movement; however, further differences may be present in contractions that involve more complex movements such as forearm rotation and shoulder adduction. Finally, this study only evaluated young female subjects. As MU activity and spinal control may differ between males and females as well as between younger and older individuals it is important to evaluate sex and age differences in future studies. This is important to understand spinal 45  integration in the functional control of movement between males and females and how these control strategies change as we age. Differences with aging may be even greater than those observed previously for isometric and anisometric contractions. Quantification of the spinal network during functional movement will in turn, allow research to determine ways to help older adults maintain daily abilities.   46  Chapter 6: Conclusion  The four contractions (waterbottle drink, waterbottle lift, anisometric and isometric) were matched for load and duration. The isometric contraction required less muscle activity (measured via surface EMG) to execute while the three dynamic contractions (anisometric, waterbottle lift and waterbottle drink) all had similar surface EMG. The waterbottle drink contraction had a higher discharge rate, higher discharge rate variability, and lower steadiness than the other contraction types. Recruitment threshold did not differ between the 4 contraction types. This highlights that that the functional task required unique spinal control strategies to execute the movement. It is clear that the MU recruitment in these tasks is based more on absolute load while rate coding is a key factor responsible for controlling functional movement. This is the first study to evaluate motor units in functional tasks and it is clear that these tasks cannot be assumed to have the same mechanistic control as anisometric contractions.    47  References  Alternburg, T.M., de Ruiter, C.J., Verdijk, P.W.L., van Mechelen, W., & de Haan, A. (2009). Vastus lateralis surface and single motor unit electromyography during shortening, lengthening and isometric contractions corrected for mode-dependent differences in force-generating capacity. Acta Physiological, 196(3), 315-328. Andrew, P.D. (1985). Motor unit activity under low tensions as muscle length changes. American Journal of Physical Medicine, 64(5), 235-254. Basmajian, J.V. (1963). Control and training of individual motor units. Science, 141 (3579), 440-441. Bawa, P., & Jones, K.E. (1999). Do lengthening contractions represent a case of reversal in recruitment order? Progress in Brain Research, 123, 215-220. Brown, R.E., Edwards, D.L., & Jakobi, J.M. (2010). Sex differences in force steadiness in three positions of the forearm. European Journal of Applied Physiology, 110(6), 1251-1257. Burnett, R.A., Laidlaw, B.H., & Enoka, R.M. (2000). Coactivation of the antagonist muscle does not covary with steadiness in old adults. Journal of Applied Physiology, 89(1), 61-71. Davids, K., Bennet, S., & Newell, K.M. (Eds.) (2006). Movement system variability. Champaign, Il: Human Kinetics. De Luca, C.J., &Erim, Z. (1994). Common drive of motor units in regulation of muscle force. Trends in Neuroscience, 17(7), 299?305. Del Valle, A., & Thomas, C.K. (2005). Firing rates of motor units during strong dynamic contractions. Muscle and Nerve, 32(3), 316-325. Duchateau, J., & Baudry, S. (2013). Insights into the neural control of eccentric contractions. Journal of Applied Physiology, In Press. 48  Enoka, R.M. (1995). Morphological features and activation patterns of motor units. Journal of Clinical Neurophysiology, 12(6), 538-599.  Enoka, R.M. (1996). Eccentric contractions require unique activation strategies by the nervous system. Journal of Applied Physiology, 81(6), 2339-2346. Fang, Y., Siemionow, V., Sahgal, V., Xiong, F., & Yue, G.H. (2001). Greater movement-related cortical potential during human eccentric versus concentric muscle contractions. Journal of Neurophysiology, 86(4), 1764-1772. Ganesh, S.P., Fried, L.P., Taylor, D.H., Pieper, C.F., & Hoenig, H.M. (2011). Lower extremity physical performance, self-reported mobility difficulty, and use of compensatory strategies for mobility by elderly women. Archives of Physical Medicine and Rehabilitation, 92(2), 228-235. Graves, A.E., Kornatz, K.W., & Enoka, R.M. (2000). Older adults use a unique strategy to lift inertial loads with the elbow flexor muscles. Journal of Neurophysiology, 83(4), 2030-2039. Harwood, B., Davidson, A.W., & Rice, C.L. (2010). Motor unit discharge rates of anconeus muscle during high-velocity elbow extensions. Experimental Brain Research, 208(1), 103-113. Harwood, B., Edwards, D.L., & Jakobi, J.M. (2008). Age- and sex-related differences in muscle activation for a discrete functional task. European Journal of Applied Physiology, 103(6), 677-686. Heckman, C.J., Gorassini, M.A.,  Bennet, D.J. (2005). Persistent inward currents in motoneuron dendrites: implications for motor output. Muscle and Nerve, 31, 135-156.  49  Heckman, C.J., Johnson, M., Mottram, C., & Schuster, J. (2008). Persistent inward currents in spinal motoneurons and their influence on human motoneuron firing patterns. The Neuroscientist, 14(3), 264-275. Henneman, E. (1957). Relation between size of neurons and their susceptibility to discharge. Science, 126(3287), 1345-1347. Henneman, E., & Olson, C.B. (1965). Relations between structure and function in the design of skeletal muscles. Journal of Neurophysiology, 28(3), 51-598. Hodson-Tole, E.F., & Wakeling, J.M. (2008). Motor unit recruitment for dynamic tasks: current understanding and future directions. Journal of Comparative Physiology B, 179(1), 57-66. Hoffer, J.A., Loeb, G.E., Sugana, N., Marks, W.B., O?Donovan, M.J., & Pratt, C.A. (1987). Cat hindlimb motoneurons during locomotion. III. Functional segregation in sartorious. Journal of Neurophysiology, 57(2), 554-562. Hunter, S.K., Ryan, D.L., Ortega, J.D., & Enoka, R.M. (2002). Task differences with the same load torque alter the endurance time of submaximal fatiguing contractions in humans. Journal of Neurophysiology, 88(6), 3087-3096. Ivanova, T., Garland, S.J., & Miller, K.J. (1997). Motor unit recruitment and discharge behavior in movements and isometric contractions.  Muscle and Nerve, 20(7), 867-874. Kallio, J., Sogaard, K., Avela, J., Komi, P.V., Selanne, H., & Linnamo V. Motor unit firing behaviour of soleus muscle in isometric and dynamic contractions. PLoS One, 8(2), e53425.  Kukulka, C.G. & Clamann, H.P. (1981). Comparison of the recruitment and discharge properties of motor units in human brachial biceps and adductor pollicis during isometric contractions. Brain Research, 219, 45-55. 50  Laidlaw, D.H., Bilodeau, M., & Enoka, R.M. (2000). Steadiness is reduced and motor unit discharge is more variable in older adults. Muscle and Nerve, 23(4), 600-612. Linnamo, V., Moritani, T., Nicol, C., & Komi, P.V. (2002). Motor unit activation patterns during isometric, concentric and eccentric actions at different force levels.  Journal of Electromyography and Kinesiology, 13(1), 93-101. MacIntosh, B.R., Gardiner, P.F., & McComas, A.J. (2006). Skeletal muscle form and function ? 2nd ed. USA.  Marmon, A.R., Gould, J.R., & Enoka, R.M. (2011). Practicing a functional task improves steadiness with hand muscles in older adults. Medicine and Science in Sports and Exercise, 43(8), 1531-1537. Marmon, A.R., Pascoe, M.A., Schwartz, R.S., & Enoka, R.M. (2011). Associations among strength, steadiness, and hand function across the adult life span. Medicine and Science in Sports and Exercise, 43(4), 560-567. McArdle, W.D., Katch, F.I., Katch, V.L. (2010). Exercise Physiology - 7th ed. Philadelphia: Lippeneott Williams & Wilkins. Moritani, T., Muramatsu, S., & Muro, M. (1988). Activity of motor units during concentric and eccentric contractions. American Journal of Physical Medicine, 66(6), 338-350.  Mottram, C.J., Jakobi, J.M., Semmler, J.G., & Enoka, R.M. (2005). Motor-unit activity differs with load type during a fatiguing contraction. Journal of Neurophysiology, 93(3), 1381-1392. Nardone, A., Romano, C., & Schieppati, M. (1989). Selective recruitment of high-threshold human motor units during voluntary isotonic lengthening of active muscles. Journal of Physiology, 409, 451-471. 51  Oldfield, R.C. (1971). The assessment and analysis of handedness: the edinburgh inventory. Neuropsychologia, 9, 97-113. Seeley, R., VanPutte, C., Regan, J., & Russo, A. (2011). Anatomy and Physiology ? 9th ed. New York: McGraw Hill. Seki K., & Narusawa, M. (1996). Firing rate modulation of human motor units in different muscles during isometric contraction with various forces. Brain Research, 719(1-2), 1-7. Semmler, J.G., Kornatz, K.W., Dinenno, D.V., Zhou, S., & Enoka, R.M. (2002). Motor unit synchronisation is enhanced during slow lengthening contractions of a hand muscle. Journal of Physiology, 545, 681-695. Semmler, J.G., & Nordstrom, M.A. (1998) Motor unit discharge and force tremor in skill- and strength-trained individuals. Experimental Brain Research, 119(1), 27-38. Seynnes, O., Hue, O.A., Garrandes, F., Colson, S.S., Bernard, P.L., Legros, P., & Singh, M.A.F. (2005). Force steadiness in the lower extremities as an independent predictor of functional performance in older women. Journal of Aging and Physical Activity, 13(4), 395-408. Sogaard, K., Christensen, H., Jensen, B.R., Finsen, L., & Sjogaard, G. (1996). Motor control and kinetics during low level concentric and eccentric contractions in man. Electroencephalography and Clinical Neurophysiology, 101(5), 453-460. Stotz, P.J., & Bawa, P. (2001). Motor unit recruitment during lengthening contractions of human wrist flexors. Muscle and Nerve, 24(11), 1535-1541. Tax, A.A., Denier van der Gon, J.J., Gielen, C.C., & van den Tempel, C.M. (1989). Differences in the activation of m. biceps brachii in the control of slow isotonic movements and isometric contractions. Experimental Brain Research, 76(1), 55-63. 52  ter haar Romeny, B.M., Denier van der Gon, J.J., & Gielen, C.C.A.M. (1984). Relation between location of a motor unit in the human biceps brachii and its critical firing levels for difference tasks. Experimental Neurology, 85(3), 631-650. Theeuwen, M., Gielen, C.C.A.M., & Miller, L.E. (1994). The relative activation of muscles during isometric contractions and low-velocity movements against a load. Experimental Brain Research, 101(3), 493-505. Tracey, B.L., & Enoka, R.M. (2002). Older adults are less steady during submaximal isometric contractions with the knee extensor muscles. Journal of Applied Physiology, 92(3), 1004-1012. Verstynen, T., Diedrichsen, J., Albert, N., Aparicio, P., & Ivry, R.B. (2005). Ipsilateral motor cortex activity during unimanual hand movements relates to task complexity. Journal of Neurophysiology, 93(3), 1209-1222. Zajac, F.E., & Faden, J.S. (1985). Relationship among recruitment order, axonal conduction velocity and muscle-unit properties of type-identified motor units in cat plantaris muscle. Journal of Neurophysiology, 53(5), 1303-1322.   53  Appendices  Appendix A: Copyright Approval for Figure 4     54  Appendix B: Ethics Approval     55  Appendix C: Pre-Study Questionnaire  Date of Experiment: _________           Experimenter Name:_____________ Subject Name: _____________  Subject Code: ________________ Sex: _________    DOB (mm/dd/yyyy):____________ Weight (kg): _________   Height (cm): _________________ Dominant Hand:   Right  or  Left Mailing Address (For Experiment Findings Only): ________________________ _________________________________________________________ Phone Number: _________________ Are you a regular smoker?   Yes No If yes, how often? _________________________________________________________ Have you had surgery in the past year? Yes No    If yes, what type? _____________________________________________ _________________________________________________________ Have you been diagnosed by a health professional as having any of the following? (Check all that apply, and be specific where applicable) Heart Trouble:_________   Arthritis:_________ High Blood Pressure:_________  High Cholesterol: _________ Cardiac Pacemaker:_________  Electronic Implant: _________ Stroke:_________    Back Problems: _________ Muscle problems:_________  Bone or Joint disorder: _________ 56  Previous Injury:_________  Alcoholism: _________ Diabetes:_________   Depression: _________ Migraines: _________ Do you suffer from any allergies? (Include hay fever, sinus problems, and skin sensitivities) _________________________________________________________ _________________________________________________________ _________________________________________________________ Do you have difficulty hearing? ____________________________________ Do you have difficulty seeing? _____________________________________ Other health problems? _________________________________________________________ _________________________________________________________ Are you currently using any medications? _________________________________________________________ _________________________________________________________  Please include any other additional pertinent information that you may feel to be beneficial to know while conducting this study. Thank you for you participation.   _________________________________________________________ _________________________________________________________   57  Appendix D: Subject Characteristic Data  Subject  # Age (years) Weight (kg) Height (cm) 1 27 64 173 2 20 63 172 3 23 50 163 4 29 58 160 5 23 57 163 6 20 70 179 7 20 65 165 8 21 59 152 9 24 56 163 10 22 55 167 11 24 52 158 12 20 71 176 13 20 50 173 Average 22.5 59.2 166.5 SD 2.9 7.0 7.8  Subject measurements taken prior to testing. kg, kilograms; cm, centimetres; SD, standard deviation.   

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.24.1-0074310/manifest

Comment

Related Items