Effect of static stretching of the biceps brachii on torque, electromyography, and mechanomyography during concentric isokinetic muscle actions

The purpose of this study was to determine the effect of an acute static stretching bout of the biceps brachii on torque, electromyography (EMG), and mechanomyography (MMG) during concentric isokinetic muscle actions. Eighteen (men, n = 10; women, n = 8) adult subjects (M +/- SD age = 22.7 +/- 2.8 years; weight 78.0 +/- 17.0 kg; height = 177.9 +/- 11.0 cm) performed maximal isokinetic (30 and 270degrees(.)s(-1)) forearm flexion strength testing on 2 occasions while EMG and MMG were recorded. Subjects were randomly assigned to stretching (STR) or nonstretching (NSTR) protocols before strength testing. Two-way ANOVAs with repeated measures revealed significantly (p less than or equal to 0.05) greater torque for NSTR (M +/- SEM = 36.9 +/- 3.3 N(.)m) vs. STR (35.2 +/- 3.3 N(.)m), significantly greater MMG amplitude for STR vs. NSTR for 30degrees(.)s(-1) (STR = 93.5 +/- 14.4 mV; NSTR = 63.1 +/- 10.6 mV) and 270degrees(.)s(-1) (STR = 207.6 +/- 35.6 mV; NSTR 136.4 +/- 31.7 mV), and no difference in EMG amplitude. These results indicate that a greater ability to produce torque without prior stretching is related to the musculotendinous stiffness of the muscle rather than the number of motor units activated. This suggests that performing activities that reduce muscle stiffness (such as stretching), may be detrimental to performance.