Abstract
We examined the effects of a submaximal voluntary elbow flexor contraction protocol on measures of corticospinal excitability and postactivation potentiation of evoked muscle forces and if these measures were state‐dependent (rest vs. voluntary muscle contraction). Participants completed four experimental sessions where they rested or performed a 5% maximum voluntary contraction (MVC) of the elbow flexors prior to, immediately, and 5 min following a submaximal contraction protocol. During rest or 5% MVC, transcranial magnetic stimulation, transmastoid electrical stimulation, electrical stimulation of biceps brachii motor point and Erb's point were elicited to induce motor‐evoked potentials (MEPs), cervicomedullary MEPs (CMEPs), potentiated twitch (PT) force, and maximal muscle compound action potential (M max), respectively prior to, immediately, and 5 min postcontraction protocol. MEP amplitudes increased (215 and 165%Mmax, P ≤ 0.03) only at 1 and 6s postcontraction protocol, respectively during rest but not 5% MVC. CMEP amplitudes decreased during rest and 5% MVC (range:21–58%M max, P ≤ 0.04) for up to 81 sec postcontraction protocol. Peak twitch force increased immediately postcontraction protocol and remained elevated for 90 sec (range:122–147% increase, P < 0.05). There was a significant positive correlation between MEP and PT force during rest (r = 0.88, P = 0.01) and a negative correlation between CMEP and PT force during rest (r = −0.85, P < 0.02 and 5% MVC (r = −0.96, P < 0.01) immediately postcontraction protocol. In conclusion, the change in corticospinal and spinal excitability was state‐ and time‐dependent whereas spinal excitability and postactivation potentiation were time‐dependent following the contraction protocol. Changes in corticospinal excitability and postactivation potentiation correlated and were also state‐dependent.
Highlights
The malleability of central nervous system excitability and evoked muscle twitch force is dependent on muscle contractile history
Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society
Motor evoked potential (MEP) amplitudes can double in size (Samii et al 1996; Norgaard et al 2000; Balbi et al 2002; Aboodarda et al 2015), whereas cervicomedullary MEP (CMEP) amplitudes can be reduced to half its size following submaximal muscle contractions compared with precontraction values (Aboodarda et al 2015)
Summary
The malleability of central nervous system excitability and evoked muscle twitch force is dependent on muscle contractile history. Postexercise facilitation and postexercise depression (i.e., an increase and decrease, respectively in the evoked potential amplitude) of corticospinal excitability occurs in fresh and fatigued muscles including the biceps brachii (Sacco et al 1997; Gandevia et al 1999; Norgaard et al 2000; Humphry et al 2004; Aboodarda et al 2015), first dorsal interosseous (McDonnell and Ridding 2006; Giesebrecht et al 2011; Teo et al 2012), extensor carpi radialis (Samii et al 1996), flexor carpi radialis (Brasil-Neto et al 1993), thenar (Zanette et al 1995; Balbi et al 2002) and soleus (Norgaard et al 2000) following contraction protocols of varying degrees of contraction intensities and durations. It is likely that postexercise facilitation and postexercise depression following voluntary contractions differ when measured during rest compared to a voluntary muscle contraction
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