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ACUTE EFFECTS OF PASSIVE STRETCHING ON THE ELECTROMECHANICAL DELAY AT SHORT AND LONG MUSCLE LENGTHS

Abstract

Lauren M. Marquess1, Omar M. Rehman1, Jonathan D. Miller1, Jeremy Lippman1, Eric M. Mosier1, Michael A. Trevino1, and Trent J. Herda1; e-mail: lmarquess@ku.edu; 1University of Kansas, Lawrence, Kansas

Electromechanical delay (EMD) is a measure of the time lag between the initial electrical stimulus and the onset of torque production. The EMD has been reported to increase following 20 mins of passive stretching (PS) of the plantarflexors at a 90° degree joint angle (neutral), which is believed to be the result of a decrease in muscle stiffness. However, it is unknown the influence that PS of the plantarflexors has on the EMD at short and long muscle lengths. PURPOSE: The purpose of this study was to examine the effects of 4 minutes of PS on the EMD at a short and long muscle length before (pre-) and after (post-) PS. METHODS: Thirteen healthy men (age = 21.54 ± 2.67 yrs;) performed the EMD assessments before and after 8 passive stretches that lasted 30 seconds each for a total of 4 minutes of PS. To measure EMD (ms), a single electrical stimulus was applied to the tibial nerve. The resulting twitch torque was measured with the torque signal from the isokinetic dynamometer. An electromyographic (EMG) sensor was placed on the soleus to measure the M-wave from the electrical stimulus. The short muscle length was 20° plantarflexion (PF) from neutral, whereas, the long muscle length was 15° dorsisflexion (DF) from neutral. The difference in time from the start of the M-wave to the onset of torque production was calculated manually by an experienced investigator (LM) with a custom written LabVIEW (v 11) software program. For the statistical analysis, a 2-way repeated-measures ANOVA (time [pre-PS vs. post-PS] x muscle length [PF vs. DF]) was used to analyze possible differences in the EMD as a result of PS. RESULTS: There was no 2-way interaction (p = 0.089) and no main effect for time (p = 0.239), however, there was a main effect for length (p < 0.001). The EMD for the long muscle length (6.64 ± 0.94 ms) was greater than the short muscle length (4.67 ± 1.07 ms). There were not significant differences in EMD pre- to post-PS. CONCLUSION: The lack of a signicant increase in EMG following PS may be the result of a relatively short duration of PS (i.e., 20 vs 4 mins). In addition, the transmission of force at DF is an longer absolute distance than PF and, therefore, EMD duration was greater.

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