Acute Effects of Dynamic Stretching on Mechanical Properties Result From both Muscle-Tendon Stretching and Muscle Warm-Up

We investigated the acute effects of dynamic stretching on mechanical properties of plantar flexor muscles and tested the hypothesis that it would result from an interaction between muscle-tendon stretching and muscle warm-up. To test the stretching effect, dynamic stretching (DS) was compared to static stretching (SS). To test the warm-up effect, DS was compared to submaximal isometric muscle activity (SIMA) with similar contraction intensity. A control condition served as reference. These four conditioning activities were time matched (2x20s) and tested on separate days on 13 volunteers. Electrical neurostimulation was applied to investigate muscle mechanical properties (peak doublet torque (PDT) and rate of torque development (RTD)), before assessing maximal voluntary isometric torque (MVIT). Passive torque and muscle fascicles length, were measured respectively with a dynamometer and ultrasonography during a maximal passive dorsiflexion. These parameters were recorded before and after each conditioning activities. MVIT, PDT, RTD and fascicles length remained unaffected, while passive torque was significantly reduced (-11.6 +/- 14.8%) after DS. SS significantly decreased MVIT (-7.7 +/- 3.8%) and enhanced fascicles length (45.3 +/- 49.2%), whereas SIMA increased PDT (5.8 +/- 5.2%) and RTD (7.4 +/- 8.3%) without affecting passive torque or fascicles length. These results may suggest that, during dynamic stretching, muscle-tendon stretching effects would partly counteract muscle warm-up effects.