Passive muscle stretching impairs rapid force production and neuromuscular function in human plantar flexors

Purpose We examined the effect of muscle stretching on the ability to produce rapid torque and the mechanisms underpinning the changes. Methods Eighteen men performed three conditions: (1) continuous stretch (1 set of 5 min), (2) intermittent stretch (5 sets of 1 min with 15-s inter-stretch interval), and (3) control. Isometric plantar flexor rate of torque development was measured during explosive maximal voluntary contractions (MVC) in the intervals 0–100 ms (RTD V100 ) and 0–200 ms (RTD V200 ), and in electrically evoked 0.5-s tetanic contractions (20 Hz, 20 Hz preceded by a doublet and 80 Hz). The rate of EMG rise, electromechanical delay during MVC (EMD V ) and during a single twitch contraction (EMD twitch ) were assessed. Results RTD V200 was decreased ( P < 0.05) immediately after continuous (− 15%) and intermittent stretch (− 30%) with no differences between protocols. The rate of torque development during tetanic stimulations was reduced ( P < 0.05) immediately after continuous (− 8%) and intermittent stretch (− 10%), when averaged across stimulation frequencies. Lateral gastrocnemius rate of EMG rise was reduced after intermittent stretch (− 27%), and changes in triceps surae rate of EMG rise were correlated with changes in RTD V200 after both continuous ( r = 0.64) and intermittent stretch ( r = 0.65). EMD V increased immediately (31%) and 15 min (17%) after intermittent stretch and was correlated with changes in RTD V200 ( r = − 0.56). EMD twitch increased immediately after continuous (4%), and immediately (5.4%), 15 min (6.3%), and 30 min after (6.4%) intermittent stretch ( P < 0.05). Conclusions Reductions in the rate of torque development immediately after stretching were associated with both neural and mechanical mechanisms.