Muscle and joint responses during and after static stretching performed at different intensities.

PURPOSE: We investigated the effects of plantarflexor static stretching of different intensities on the medial gastrocnemius (GAS) shear elastic modulus, GAS fascicle length and ankle passive torque-angle responses during and after stretching.
METHODS: Participants performed three stretching sessions of different intensities: 40 % (R40) of maximal dorsiflexion range of motion (ROM), 60 % (R60) of ROM, and 80 % (R80) of ROM. Each stretching lasted 10 min. The GAS architecture, GAS shear elastic modulus, ankle passive torque-angle, and muscle activity were assessed before, during, and after the stretching.
RESULTS: The absolute and relative (i.e., normalized to the static stretching start value) GAS shear elastic modulus relaxation varied across stretching intensities. The absolute passive torque relaxation varied across intensities (p < 0.05) but not when normalized to the stretching start value. No significant changes were observed in GAS fascicle length during the stretching (p = 0.93). After stretching, passive torque at a given angle was significantly decreased for R60 [-0.99 ± 0.59 Nm (-6.5 ± 3.8 %), p < 0.001] and R80 [-1.05 ± 1.12 Nm (-6.8 ± 6.3 %), p = 0.004], and GAS shear elastic modulus decreased only for the R80 [-9.3 ± 7.2 kPa (-14.1 %), p = 0.003]. No significant correlations were found between the magnitude of relaxation during stretching and post-stretching effect in the GAS shear elastic modulus or ankle passive torque variables. No significant relation was found between the shear elastic modulus and the ankle passive torque responses during and after stretching.
CONCLUSION: The effects of stretching on joint passive torque do not reflect changes in the medial gastrocnemius shear elastic modulus, and these responses to stretching depend on its intensity.