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

Abstract

This study investigated whether the specific motor control strategy reported for eccentric muscle actions is dependent on muscle mechanical behavior. Motor evoked potentials, Hoffman reflex (H-reflex), fascicle length, pennation angle, and fascicle velocity of soleus muscle were compared between isometric and two eccentric conditions. Ten volunteers performed maximal plantarflexion trials in isometric, slow eccentric (25°/s), and fast eccentric (100°/s) conditions, each in a different randomized testing session. H-reflex normalized by the preceding M wave (H/M) was depressed in both eccentric conditions compared with isometric (P < 0.001), while no differences in fascicle length and pennation angle 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. There were no differences in motor evoked potential size between conditions, and silent period was shorter for both eccentric conditions compared with isometric (P = 0.009). Taken together, the present results corroborate the hypothesis that the central nervous system has an unique activation strategy during eccentric muscle actions and suggest that sensory feedback does not play an important role in modulating these muscle actions.