Effect of selective stretching of the flexor digitorum longus on the exercise-induced muscle stiffness change

Medial Tibial Stress Syndrome is associated with the stiffness of flexor digitorum longus (FDL) muscle. Therefore, it is necessary to reduce the load on FDL. Stretching has been reported to immediately reduce muscle stiffness and decrease maximal muscle strength. Thus, stretching the FDL may reduce its stiffness and stress. Additionally, the decrease in muscle strength due to stretching may be compensated by other cooperative muscles. This study aimed to determine how selective stretching of the FDL before exercise affects the stiffness of the FDL and its cooperative muscles after exercise.

Twenty-one healthy young men were enrolled in this crossover study. The elastic modulus of the FDL, tibialis posterior (TP), soleus, and flexor hallucis longus muscles were measured. The intervention trial involved selective stretching of the FDL. Subsequently, an eccentric ankle inversion exercise was performed, and the elastic modulus of each muscle was measured. The control trial consisted of resting in a sitting position instead of stretching.

A significant interaction was observed for the elastic modulus of the FDL, the elastic modulus increased significantly only in the control trial after exercise. A main effect of timing was found only for the TP, and neither a main effect nor an interaction effect was found for any of the other muscles.

Selective stretching of the FDL muscle before exercise prevented an immediate increase in its stiffness after exercise, but there was no such effect following changes in muscle stiffness caused by exercise in the other cooperative muscles.