Effect of static stretching duration on modulation of H-reflex and tendon-reflex excitability of the soleus muscle in young men.

Stretching-induced impairments of muscle performance are attributed to neural adaptations and mechanical changes. Inhibition of muscle spindle sensitivity appears to have long-lasting effects after stretching. However, whether a dose-response relationship exists between stretching duration and muscle spindle sensitivity remains unclear. The present study aimed to reveal the effect of static stretching duration on modulation of muscle spindle sensitivity in the soleus muscle. The present study used data obtained from 19 young men. Static stretching intervention involved five 1-min stretches with 1-min intervals between stretches under maximal dorsiflexion. The Hoffmann-reflex (H-reflex) and tendon-reflex (T-reflex) were recorded from the soleus before and during stretching, at intervals between stretching. Time-course changes in H-reflex and T-reflex amplitudes from baseline (i.e., before stretching) were calculated. The H-reflex amplitude depressed 51.5%-55.2% during static stretching, and these H-reflex depressions recovered in the interval following each stretch. T-reflex amplitudes depressed 71.2%-73.5% during static stretching, and these T-reflex depressions remained following each interval. Inhibitions of the T-reflex amplitude after the second to fifth stretches were not significantly stronger than that after the first static stretch. These results suggest that 1-min static stretching under maximal dorsiflexion achieves sufficient modulation of muscle spindle sensitivity of the soleus.