Do practical durations of stretching alter muscle strength? A dose-response study

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 (PS ₂), 4 min (PS ₄), and 8 min (PS ₈) 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%), PS ₂ (2%), PS ₄ (4%), and PS ₈ (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 PS ₄ (7%) and the PS ₈ (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 PS ₂ (8%), the PS ₄ (14%), and the PS ₈ (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.