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

Abstract

We examined the effect of muscle stretching on the ability to produce rapid torque and the mechanisms underpinning the changes. Eighteen men performed three conditions: (1) continuous stretch (1 set of 5min), (2) intermittent stretch (5 sets of 1min 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 0-100ms (RTDV100) and 0-200ms (RTDV200), and in electrically evoked 0.5-s tetanic contractions (20Hz, 20Hz preceded by a doublet and 80Hz). The rate of EMG rise, electromechanical delay during MVC (EMDV) and during a single twitch contraction (EMDtwitch) were assessed. RTDV200 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 RTDV200 after both continuous (r = 0.64) and intermittent stretch (r = 0.65). EMDV increased immediately (31%) and 15min (17%) after intermittent stretch and was correlated with changes in RTDV200 (r = -0.56). EMDtwitch increased immediately after continuous (4%), and immediately (5.4%), 15min (6.3%), and 30min after (6.4%) intermittent stretch (P < 0.05). Reductions in the rate of torque development immediately after stretching were associated with both neural and mechanical mechanisms.