Increased corticospinal inhibition following submaximal and maximal muscle activation in humans
Abstract
Following short duration, high intensity muscle activation, there is an enhancement of muscle contractile properties, termed postactivation potentiation (PAP). Corticospinal inhibition, assessed by an increased silent period (SP), was shown previously to increase following voluntary or electrically evoked PAP. Although these changes coexist, the direct effect of PAP on corticospinal inhibition has not been systematically evaluated. In 10 participants, SP duration was measured pre and post 10s maximal and submaximal, voluntary and electrically stimulated contractions. Following maximal contractions, mean twitch torque was enhanced ~180% with no enhancement at submaximal levels (~102%). The SP duration was prolonged following all conditions: ~12% post maximal voluntary and stimulated contractions, and ~5% post submaximal voluntary and involuntary contractions. These findings show that corticospinal inhibition is increased not only when the muscle is enhanced by PAP, but also following submaximal efforts inducing no PAP. Therefore, likely indicating that increases in corticospinal inhibition arise likely from afferent feedback relating to activation of the muscle rather than changes in intrinsic contractile states (PAP) per se.