Do Practical Durations of Stretching Alter Muscle Strength? A Dose-Response Study

TLDR

The study examined how 2, 4, and 8‑minute passive stretching of the plantarflexors acutely affects isometric peak torque, voluntary activation, EMG, twitch torque, twitch development rate, and range of motion over a 30‑minute recovery period. Thirteen young adults completed four randomized trials (control, 2‑min, 4‑min, 8‑min passive stretch) with measurements taken pre‑stretch, immediately post, and at 10, 20, and 30 minutes, using twitch interpolation for torque and EMG and passive dorsiflexion for ROM. Peak torque fell immediately after all conditions but returned to baseline within 10 minutes; voluntary activation, EMG, and twitch torque development were largely unchanged, while ROM increased after each stretch duration and normalized by 10 minutes, indicating that practical stretching does not impair but temporarily enhances flexibility without reducing strength.

Abstract

Purpose: To examine the time course (immediate, 10, 20, and 30 min) for the acute effects of 2, 4, and 8 min of passive stretching (PS) on isometric peak torque (PT), percent voluntary activation (%VA), EMG amplitude, peak twitch torque (PTT), rate of twitch torque development (RTD), and range of motion (ROM) of the plantarflexors. Methods: Thirteen volunteers (mean ± SD age, 22 ± 3 yr) participated in four randomly ordered experimental trials: control (CON) with no stretching, 2 min (PS2), 4 min (PS4), and 8 min (PS8) of PS. Testing was conducted before (pre), immediately after (post), and at 10, 20, and 30 min poststretching. The PS trials involved varied repetitions of 30-s passive stretches, whereas the CON trial included 15 min of resting. PT, %VA, EMG amplitude, PTT, and RTD were assessed during the twitch interpolation technique, whereas ROM was quantified as the maximum tolerable angle of passive dorsiflexion. Results: PT decreased (P ≤ 0.05) immediately after all conditions [CON (4%), PS2 (2%), PS4 (4%), and PS8 (6%)] but returned to baseline at 10, 20, and 30 min poststretching. %VA and EMG amplitude were unaltered (P > 0.05) after all conditions. PTT and RTD decreased (P ≤ 0.05) immediately after the PS4 (7%) and the PS8 (6%) conditions only; however, these changes were not sufficient to alter voluntary force production. There were also increases (P ≤ 0.05) in ROM after the PS2 (8%), the PS4 (14%), and the PS8 (13%) conditions that returned to baseline after 10 min. Conclusion: Practical durations of stretching (2, 4, or 8 min) of the plantarflexors did not decrease isometric PT compared with the CON but caused temporary improvements in the ROM, thereby questioning the overall detrimental influence of PS on performance.