Muscle length effect on corticospinal excitability during maximal concentric, isometric and eccentric contractions of the knee extensors

Abstract

Neural control of eccentric contractions differs from that of concentric and isometric contractions, but no previous study has compared responses to motor cortex stimulations at long muscle lengths during such contraction types. This study compared the effect of muscle length on corticospinal excitability between maximal concentric, isometric and eccentric contractions of the knee extensors. Twelve males performed 12 maximal concentric, isometric and eccentric voluntary contractions (36 contractions in total), separated by a 5-min rest between contraction types. The 12 contractions for the same contraction type were performed every 10 s, and transcranial magnetic stimulations (first 8 contractions) and electrical femoral nerve stimulations (last 4 contractions) were superimposed alternatively at 75° and 100° of knee flexion. Average motor evoked potential amplitude, normalized to the maximal M wave amplitude (MEP/M), and cortical silent period (CSP) duration were calculated for each angle, and compared among the contraction types. MEP/M was lower −23% and −28%, respectively) during eccentric than both concentric and isometric contractions at 75°, but similar between contraction types at 100° (P < 0.05). CSP duration was shorter (−12% and −10%, respectively) during eccentric than both concentric and isometric contractions at 75°, but longer (+11% and +9%, respectively) during eccentric contractions at 100° (P < 0.05). These results show that corticospinal excitability during eccentric contractions is angle dependent such that cortical inhibitory processes are greater with no alteration of corticospinal excitability at 100°, while this control is reversed at 75°.

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