Understanding changes in peripheral and central excitability following submaximal contractions

Abstract

The objective of this thesis was to examine the effects of brief (2s), non-fatiguing, submaximal (50% of MVC) and intermittent (2s on, 2s off) contractions on measures of central and peripheral excitability. Nine resistance-trained males completed a contraction protocol consisting of 5 such contractions of the elbow flexors. Pre-, immediately post-, and 5 minutes post-contractions the participants received transcranial magnetic stimulation (TMS), transmastoid electrical stimulation (TMES), peripheral nerve stimulation, and motor point stimulation to elicit motor-evoked potentials (MEPs), cervicomedullary-evoked potentials (CMEPs), maximal muscle compound action potentials (Mmax), and peak twitch force (PT), respectively. All MEPs and CMEPs were normalized to Mmax. In addition, correlations between central and peripheral excitability were analyzed in order to determine if the two are separate entities or related. Finally, all measurements were taken both at rest, as well as during a slight (5% of MVC) contraction. This allowed us to determine if the changes in central and peripheral excitability, as well as the correlations between the two, were state-dependent. Results showed an increase in corticospinal excitability (CSE) that was state-dependent, a decrease in spinal excitability that was not state-dependent, and an increase in muscle excitability that was not state-dependent following the contraction protocol. There was a positive correlation between CSE and peripheral excitability that was state-dependent, and a negative correlation between spinal excitability and peripheral excitability that was not state-dependent. Since some of the trends observed were state-dependent, the major finding of this thesis is that results obtained at rest should not be generalized to movement situations.