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

Area of Science:

• Neuromuscular Physiology
• Sports Science
• Rehabilitation Medicine

Background:

• Passive stretching (PS) is commonly used to increase range of motion (ROM).
• The acute effects of varying durations of PS on neuromuscular performance are not fully understood.
• Investigating the time course of these effects is crucial for optimizing training and recovery protocols.

Purpose of the Study:

• To investigate the acute effects of 2, 4, and 8 minutes of passive stretching (PS) on plantarflexor muscle function.
• To examine the time course of these effects, assessing immediate and up to 30 minutes post-stretching.
• To evaluate changes in isometric peak torque (PT), voluntary activation (%VA), EMG amplitude, peak twitch torque (PTT), rate of twitch torque development (RTD), and ROM.

Main Methods:

• Thirteen healthy volunteers underwent four randomized trials: control (CON), 2 min (PS2), 4 min (PS4), and 8 min (PS8) of PS.
• Measurements of PT, %VA, EMG amplitude, PTT, and RTD were taken using the twitch interpolation technique.
• ROM was assessed as the maximum passive dorsiflexion angle.
• Testing occurred pre-stretching, immediately post-stretching, and at 10, 20, and 30 minutes post-stretching.

Main Results:

• Isometric peak torque (PT) showed a small, transient decrease immediately after all conditions but returned to baseline by 10 minutes.
• Percent voluntary activation (%VA) and EMG amplitude remained unchanged across all conditions.
• Peak twitch torque (PTT) and rate of twitch torque development (RTD) decreased only after PS4 and PS8, but these changes did not affect voluntary force production.
• Range of motion (ROM) significantly increased after PS2, PS4, and PS8, returning to baseline within 10 minutes.

Conclusions:

• Practical durations of passive stretching (2-8 minutes) did not impair isometric plantarflexor strength compared to a control condition.
• Passive stretching resulted in temporary improvements in range of motion.
• These findings challenge the notion that passive stretching inherently leads to performance decrements.