Relationship between changes in passive properties and muscle strength after static stretching

BACKGROUND The association between decreased muscle strength of rate of force development (RFD) immediately after static stretching (SS) and change in muscle stiffness or muscle slack has remained unclear. OBJECTIVE This study aimed to investigate the association between changes in muscle strength and RFD and muscle stiffness or muscle slack immediately after SS. METHODS Sixteen healthy male non-athlete volunteers participated in this study. The maximal voluntary contraction torque and shear elastic modulus of medial gastrocnemius muscle were measured before and after 300 s of SS intervention. RESULTS The results showed that maximal voluntary contraction torque and RFD at 100, 150, and 200 ms decreased significantly after the 300-s SS (p < 0.01). Additionally, shear elastic modulus at 0° (decrease in muscle stiffness) and slack angle decreased (increase in slack length) significantly after the 300-second SS (p < 0.01). However, no significant association was observed between changes in muscle strength and changes in mechanical properties of the MG. CONCLUSION These results suggested that the decrease in muscle strength and RFD could not be associated with changes in the passive mechanical properties of the medial gastrocnemius muscle.