J.W. Kepple, N.P. Disser, S.E. Lamarche, J.C. Turner, R.S. McCulloch

Gonzaga University, Spokane, WA

PURPOSE: This study aimed to examine the effects of stretching the antagonist muscle on force production and muscle activity characteristics of both the agonist and the antagonist during a maximal isometric contraction.METHODS: Thirteen males and seven females (age mean ± SD, 21.05 ± 0.92 years) participated in this study. Subjects performed three separate trials involving maximum isometric biceps contractions with differing interventions of static stretching. The subjects were randomly assigned the stretching (Trial S) or no-stretch (Trial NS) protocol to perform during the first two sessions. Trial S included a 30 s static triceps stretch, to mild discomfort, performed by the subjects between contractions. The third session (Trial C) was completed after two weeks of the same triceps stretch performed three times per day, for 30 s each time. Electrodes were placed on the muscle belly of the biceps as well as the triceps. For each trial, 3 maximal voluntary contractions (MVC) were performed for the biceps as well as the triceps. Peak forces were measured with an in-line force transducer. All EMG values were normalized to their MVC EMG values for each trial; biceps activity, triceps activity, and biceps/triceps ratio values were all measured and calculated. To evaluate for significant findings (p<.05), a repeated measures ANOVA was used to compare muscle activation variables and force production within subjects for the S, NS, and C trials.RESULTS: There was a negative trend in maximal biceps force production between Trial NS (207.7 ± 75.5 N) and Trial C (202.0 ± 70.2 N), with a 5.7 N decrease in force production (p= 0.09). No differences (p>0.05) were detected between mean biceps force (NS: 207.7 ± 75.6 N, S: 206.5 ± 77.7 N, C: 202.0 ± 70.2 N), biceps EMG (NS: 0.939 ± 0.122 %MVC, S: 0.923 ± 0.183 %MVC, C: 0.967 ± 0.177 %MVC) and triceps EMG (NS: 0.174 ± 0.091%MVC, S: 0.173 ± 0.111 %MVC, C: 0.182 ± 0.123 %MVC), and biceps/triceps ratio (NS: 7.36 ± 4.59, S: 8.13 ± 6.44, C: 8.18 ± 6.53) between the NS, S, and C trials. CONCLUSION: There were observable trends, though not significant, suggesting that stretching the antagonist muscle may impair the agonist muscles’ ability to produce force chronically. As the observed changes were small, additional work with more subjects is warranted to evaluate for potential negative effects on performance.

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