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 2012

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RESEARCH POSTER PRESENTATION DESIGN © 2012 www.PosterPresentations.com  Individuals utilizing equipment with vibratory elements demonstrate increased musculoskeletal and neurovascular impairments related to reduced strength and muscle fatigue (1).  However, the reduced MVC may also be due to the disruption in E-C coupling (2).  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). Introduction Methods Figure 5: Peak torque during MVCs. No significant difference was found across the conditions. Conclusion  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. 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.  The purpose of this study was to investigate the extent to which E-C coupling plays a role in force attenuation following vibration. Results Objective L.M. Cornish, V.M. Feige, A.D. Guenter, C.L. Kliewer, E.A. Mellis Is the decrease in maximal voluntary contraction following tibialis anterior tendon vibration accompanied by a disruption in excitation contraction coupling? 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).  Methods Results  Subjects:  9 female and 1 male, age 33 (10.6)  Individuals sat in a Biodex chair with 90° of hip and knee flexion.                 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. Figure 1: Equipment set-up. The dominant foot and leg were immobilized while ankle dorsiflexion was measured. 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 Supervisor: S.J. Garland, Ph.D.  0 10 20 30 40 50 60 70 80 90 Vibration No Vibration P e a k  T o rq u e  ( N m ) Pre Post Vibration No Vibration Singlet Pre Post Pre Post Peak Torque (Nm) 2.4 ± 1.0 5.2 ± 10.8 2.3 ± 1.1 2.0 ± 0.9 Time to Peak Torque (ms) 110 ± 15.9 113 ± 13.4† 106 ± 10.5 109 ± 10.9†  Doublet Peak Torque (Nm) 8.9 ± 2.8 8.7 ± 3.3 8.4 ± 1.9 7.9 ± 1.8 Time to Peak Torque (ms) 113 ± 41.2 117 ± 43.6‡ 123 ± 12.6 126 ± 10.8‡  10 Hz Peak Torque (Nm) 8.4 ± 3.8 6.7 ± 3.1* 7.4 ± 3.1 6.5 ± 2.9*  50 Hz Peak Torque (Nm) 27.2 ± 11.5 25.5 ± 9.3 24.0 ± 7.1 25.2 ± 5.7 Time to Peak Torque (ms) 205 ± 38.1 217 ± 16.4 210 ± 21.4 218 ± 11.8 0 0.1 0.2 0.3 0.4 0.5 0.6 Vibration No Vibration 1 0  H z  /  5 0  H z  R a ti o  Pre Post 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 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. 0 2 4 6 8 0.0 0.2 0.4 0.6 0.8 1.0  Time (sec) 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. 0.15 0.19 0.28 0.24 0 10 20 30 40 50 0.0 0.8 0.0 0.8 0.0 0.8 Time (sec) 0.0 0.8  Pre-vibration Post-vibration Pre-rest Post-rest %  V o lu n ta ry  A c ti v a ti o n 

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