Short-interval cortical inhibition and corticomotor excitability with fatiguing hand exercise: a central adaptation to fatigue?

Abstract

The central processes occurring during fatiguing exercise are not well understood, however transcranial magnetic stimulation (TMS) studies have reported increases both in corticomotor excitability, as measured by the motor-evoked potential (MEP) amplitude, and in long-interval intracortical inhibition, as measured by the duration of the post-MEP silent period. To determine whether short-interval cortical inhibition (SICI) is modulated by fatiguing exercise, we used single and paired-pulse TMS to measure MEP amplitude and SICI for the first dorsal interosseous (FDI) and abductor digiti minimi (ADM) muscles of the hand during, and for 20 min after, a 10-min intermittent maximal voluntary abduction of the index finger designed to fatigue the FDI muscle. For the FDI, the index of SICI increased at the onset of exercise (from 0.25+/-0.05 to 0.55+/-0.11, P < 0.05) and then decreased progressively as force declined. At the beginning of recovery, SICI again increased (0.57+/-0.11, P < 0.05) and remained elevated for the 20-min recovery period. In contrast, SICI for ADM did not change during or after exercise. MEP amplitude for both the FDI and ADM increased above baseline during exercise and then decreased below baseline during the recovery period. These results demonstrate that there are significant changes in SICI during and after a fatiguing exercise protocol that are isolated to the representation of the fatigued muscle. The inter-relationship between the changes in excitation and inhibition suggests the presence of a measured and adaptive process of modulation in central excitation and inhibition acting to increase corticomotor drive to the exercising muscle as fatigue is developing.

Nonexercise movement in elderly compared with young people

“…Changes in, or dysregulation of, central mechanisms that modulate or regulate activity may occur with aging (14,41,45). Alternatively, there may be a change in the central perception of fatigue, resulting in a lower threshold for activity cessation (2,12,31,42). There may be dysfunction or dysregulation in peripheral neurons or intrinsic muscle function limiting the activity that a subject may be able to perform.…”

Cognitive fatigue of executive processes: Interaction between interference resolution tasks

“…Neural correlates of resource depletion related fatigue effects have also been observed in lower-level systems. For example, reduced functional activation of primary motor cortex has been found following fatiguing exercise of the hand (Benwell et al, 2006). Furthermore, prolonged exposure to a visual pattern disturbs visual perception, and single cell recording show have shown that prolonged stimulation of about 30 sec fatigues visual neurons in the primary visual cortex to give a weaker response that they otherwise would (Carandini, 2000).…”

The neural control of coactivation during fatiguing contractions revisited

“…The similar time course of change for the two antagonistic muscles is surprising because the prolongation of the silent period has been often associated with impairments in the networks that generate the descending motor command (Sacco et al, 1997;Sogaard et al, 2006). Although the exact mechanisms underlying the prolongation of the cortical silent period remains to be determined (Benwell et al, 2006(Benwell et al, , 2007Taylor and Gandevia, 2001), the finding of a similar time course for both the agonist and antagonist muscles indicates that the cortical changes represented by the lengthening of the silent period are not directly related to the reduction and CMEP (n = 6) for the biceps brachii (respectively, s and D) and triceps brachii (respectively, d and N) during the fatiguing contraction and recovery. Data (mean ± S.E.M.)…”