GSS cIRcle Open Scholar Award (UBCV Non-Thesis Graduate Work)

Is the Decrease in Maximal Voluntary Contraction Following Tibalis Anterior Tendon Vibration Accompanied.. Cornish, Lisa; Feige, Victoria (Tori); Guenter, Adriana; Kliewer, Christina; Mellis, Emily 2012

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Is the decrease in maximal voluntary contraction following tibialis anterior tendon vibration accompanied by a disruption in excitation contraction coupling? L.M. Cornish, V.M. Feige, A.D. Guenter, C.L. Kliewer, E.A. Mellis Supervisor: S.J. Garland, Ph.D.  Methods  Introduction  Individuals utilizing equipment with vibratory elements demonstrate increased musculoskeletal and neurovascular impairments related to reduced strength and muscle fatigue (1).  % Voluntary Activation  1.0   However, the reduced MVC may also be due to the disruption in E-C coupling (2).  Figure 2: Subjects were exposed to a combination of 4 conditions that included 10 minutes of vibration or no vibration bracketed by MVC or electrical stimulation (ABCD, CDAB, ACBD, BDAC, ADBC).  Objective  Methods  Subjects: 9 female and 1 male, age 33 (10.6)  Individuals sat in a Biodex chair with 90° of hip and knee flexion.  Pre-rest  0.8  0.15 0.0  0.6  0.8  0.4  Post-rest  0.19  0.2 0.0  0  2  4  6  0.0 0.8  8  Figure 3: Torque trace during MVC. Black arrow denotes timing of interpolated twitch used to assess % voluntary activation. Interpolated twitch was elicited with doublet stimulation during and after MVC.  Results 0.6 10 Hz / 50 Hz Ratio   The purpose of this study was to investigate the extent to which E-C coupling plays a role in force attenuation following vibration.  0.8  Pre-vibration  Time (sec)  0.28  0.0 0.8  Post-vibration  0.24  0.0 0  10  20  30  40  50  Time (sec) 90 Figure 6: Real data figures displaying the following stimulations: 3 single twitches, doublet, 2 10 Hz and 50 Hz. Absolute values of torque labeled in figure demonstrate the decrease in torque during the vibration condition.  80  0.5 0.4 Pre Post  0.3 0.2 0.1  Peak Torque (Nm)   E-C coupling is ascertained in human subjects during functional activities (10 Hz) whereas maximal exercise (50 Hz) increases calcium in muscle beyond typical functional activation levels accounting for decreased E-C coupling (3).  Results  70 60 50  Pre Post  40 30 20  Conclusion  10  0  0 Vibration  No Vibration  Vibration  Figure 4: 10 Hz / 50 Hz ratio for peak torque. A significant decrease (p=0.007) following vibration and no vibration was observed; however, no significant difference was found across conditions.  Figure 5: Peak torque during MVCs. No significant difference was found across the conditions.  Vibration Singlet Peak Torque (Nm) Time to Peak Torque (ms)  No Vibration  No Vibration  Pre 2.4 ± 1.0 110 ± 15.9  Post 5.2 ± 10.8 113 ± 13.4†  Pre 2.3 ± 1.1 106 ± 10.5  Post 2.0 ± 0.9 109 ± 10.9†  8.9 ± 2.8 113 ± 41.2  8.7 ± 3.3 117 ± 43.6‡  8.4 ± 1.9 123 ± 12.6  7.9 ± 1.8 126 ± 10.8‡  8.4 ± 3.8  6.7 ± 3.1*  7.4 ± 3.1  6.5 ± 2.9*   Impairment in torque production by low frequency stimulation at 10 Hz suggests that the capacity to produce torque is compromised both during periods of immobilization and vibration.   E-C coupling, as indicated by the 10 Hz/50 Hz torque ratio, may not be affected by vibration.  Vibration was not found to attenuate MVC force production.  Doublet Figure 1: Equipment set-up. The dominant foot and leg were immobilized while ankle dorsiflexion was measured.   Stimulating electrodes were placed on the common peroneal nerve (CPN) just distal to the fibular head. For stimulation trials (7 singlet pulses, doublet, 10 Hz and 50 Hz), a dorsiflexion twitch was evoked via constant voltage stimulator.  E-C coupling was determined by evaluating the ratio of 10 Hz to 50 Hz peak torque.  For vibration trials, a vibrator was secured to the distal musculotendious junction of the tibialis anterior muscle. RESEARCH POSTER PRESENTATION DESIGN © 2012  www.PosterPresentations.com  Peak Torque (Nm) Time to Peak Torque (ms) 10 Hz Peak Torque (Nm) 50 Hz Peak Torque (Nm) Time to Peak Torque (ms)  27.2 ± 11.5 205 ± 38.1  25.5 ± 9.3 217 ± 16.4  24.0 ± 7.1 210 ± 21.4  25.2 ± 5.7 218 ± 11.8  Table 1: There was a significant drop in peak torque generated for pre to post comparisons for 10Hz stimulation. For the singlet stimulation, time to peak torque (mean ± SD) was significantly different between pre and post measurements in both conditions. For doublet stimulations, time to peak torque exhibited a trend towards difference in pre and post measurements. *p<0.001, †p=0.007, ‡p=0.07  References (1) Worksafe BC (2011). (2) Shinohara, M. (2005a). Medicine and Science in Sports and Exercise, 37(12), 2120-2125. (3) Cheng, A. J., & Rice, C. L. (2005). Journal of Applied Physiology. 99(4), 1446-1452.  

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