Corticospinal excitability to the biceps brachii and its relationship to postactivation potentiation of the elbow flexors

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.

Post-activation Potentiation Versus Post-activation Performance Enhancement in Humans: Historical Perspective, Underlying Mechanisms, and Current Issues

“…The use of transcranial (motor-evoked potentials; MEPs) and transmastoid (to evoke cortico-medullary evoked potentials; CMEPs) magnetic stimulations have revealed variable responses depending on many factors, including the intensity and volume of muscular efforts, the time after contraction at which testing was performed, and whether measurements were taken in resting or contracting muscles. A detailed review of these studies is beyond the scope of the current paper, however, by way of example, transient (up to a few seconds) increases in MEP amplitudes have been detected when measured at rest (Nørgaard et al, 2000; Aboodarda et al, 2015; Collins et al, 2017) but not during contraction (Collins et al, 2017) and any increases may be followed by MEP depression (Aboodarda et al, 2015), yet post-activation depression of CMEPs has been reported, even when exercise was sufficiently brief that fatigue should not have been evoked (Aboodarda et al, 2015; Collins et al, 2017). These data, combined with H-reflex data, produce a complex picture of responses of the nervous system to brief muscular efforts.…”

Transcranial direct current stimulation of primary motor cortex modulates post-contraction potentiation

“…Both the force and BB EMG activity during MVC did not significantly differ before and after the experiment (P = 0.217 and 0.880, re- Test 2 CC reflex circuitry, or (4) excitatory descending tracts. If these mechanisms are involved in PCP, the MEP magnitude would be increased during PCP 27) ; however, this was not true because it decreased during PCP (Fig. 5).…”