Acute Effects of Passive Stretching on the Electromechanical Delay and Evoked Twitch Properties in Women

Abstract

Studies have shown passive stretching may transiently decrease force and alter twitch-related properties. However, the effects of passive stretching on the electromechanical delay (EMD) in women are still unknown. PURPOSE: Studies have shown passive stretching may transiently decrease force and alter twitch-related properties. However, the effects of passive stretching on the electromechanical delay (EMD) in women are still unknown. METHODS: 20 women (mean age ± SD = 20.9 ± 2.5 yrs; body mass = 61.3 ± 8.9 kg; height = 165.3 ± 7.5 cm) volunteered for the study. Five, single-square, supramaximal transcutaneous electrical stimuli (each separated by 5 seconds) were delivered to the tibial nerve before and after passive stretching. The stretching protocol consisted of nine repetitions of passive assisted stretching designed to stretch the calf muscles. Each repetition was held for 135 seconds separated by 5-10 seconds of rest between each passive stretching repetition. An average of three pre- and post-stretching twitches were used to analyze each variable. Dependent-samples t-tests (pre- vs. post-stretching) were used to analyze the EMD, PTF, RFD, and PPM data. RESULTS: There were significant changes (P ≤ 0.05) from pre- to post-stretching for EMD (mean ± SE = 32.1 ± 0.49 and 33.4 ± 0.53 ms). However, PTF (11.9 ± 0.69 and 11.6 ± 0.60), RFD (180.6 ± 10.6 and 173.2 ± 8.4), and PPM (2.2 ± 0.19 and 2.2 ± 0.16) amplitude did not change (P > 0.05). CONCLUSIONS: These findings suggested that passively stretching the calf muscles affected the mechanical aspects of force production from the onset of the electrically-evoked twitch to the peak twitch force. These results may help explain the mechanisms underlying the stretching-induced force deficit that have been reported as either "mechanical" or "electrical" in origin.