Effects of Muscle Action Type on Corticospinal Excitability and Triceps Surae Muscle-Tendon Mechanics

This study investigated if the specific motor control strategy reported for eccentric muscle actions is dependent of muscle mechanical behavior. Motor-evoked potentials (MEP), Hoffman reflex (H-reflex), fascicle length (FL), pennation angle (PA) and fascicle velocity (FV) of soleus (SOL) muscle were compared between isometric and two eccentric conditions. Ten volunteers performed maximal plantarflexion trials in isometric, slow eccentric (25º/s) and fast eccentric (100º/s) conditions, each on a different randomized testing session. Normalized H-reflex (H/M) was depressed in both eccentric conditions as compared to isometric (P < 0.001), while no differences in FL and PA were found among conditions. Furthermore, although the fast eccentric condition had greater fascicle velocity than slow eccentric (P = 0.001), there were no differences in H/M ratio. There were no differences in MEP size between conditions, and silent period was shorter for both eccentric conditions as compared to isometric (P = 0.009). Taken together, the present results corroborates with the hypothesis that the central nervous system has an unique activation strategy during eccentric muscle actions and suggests that sensory feedback does not play an important role in modulating these muscle actions.

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