Reduced short-interval intracortical inhibition after eccentric muscle damage in human elbow flexor muscles

Abstract

Pitman BM, Semmler JG. Reduced short-interval intracortical inhibition after eccentric muscle damage in human elbow flexor muscles. J Appl Physiol 113: 929 -936, 2012. First published July 26, 2012 doi:10.1152/japplphysiol.00361.2012.-The purpose of this study was to use paired-pulse transcranial magnetic stimulation (TMS) to examine the effect of eccentric exercise on short-interval intracortical inhibition (SICI) after damage to elbow flexor muscles. Nine young (22.5 Ϯ 0.6 yr; mean Ϯ SD) male subjects performed maximal eccentric exercise of the elbow flexor muscles until maximal voluntary contraction (MVC) force was reduced by ϳ40%. TMS was performed before, 2 h after, and 2 days after exercise under Rest and Active (5% MVC) conditions with motor-evoked potentials (MEPs) recorded from the biceps brachii (BB) muscle. Peripheral electrical stimulation of the brachial plexus was used to assess maximal Mwaves, and paired-pulse TMS with a 3-ms interstimulus interval was used to assess changes in SICI at each time point. The eccentric exercise resulted in a 34% decline in strength (P Ͻ 0.001), a 41% decline in resting M-wave (P ϭ 0.01), changes in resting elbow joint angle (10°, P Ͻ 0.001), and a shift in the optimal elbow joint angle for force production (18°, P Ͻ 0.05) 2 h after exercise. This was accompanied by impaired muscle strength (27%, P Ͻ 0.001) and increased muscle soreness (P Ͻ 0.001) 2 days after exercise, which is indicative of muscle damage. When the test MEP amplitudes were matched between sessions, we found that SICI was reduced by 27% in resting and 23% in active BB muscle 2 h after exercise. SICI recovered 2 days after exercise when muscle pain and soreness were present, suggesting that delayed onset muscle soreness from eccentric exercise does not influence SICI. The change in SICI observed 2 h after exercise suggests that eccentric muscle damage has widespread effects throughout the motor system that likely includes changes in motor cortex. exercise; motor control; TMS; motor cortex UNACCUSTOMED ECCENTRIC EXERCISE involving the repetitive lengthening of muscle is known to cause significant damage to the ultrastructural and cytoskeletal components of muscle fibers (1) and an impairment in the excitation-contraction coupling process (59). The consequences of this exercise-induced muscle damage are a long-lasting decline in muscle strength, a shift in the optimal muscle length for force generation, muscle swelling, and an increase in passive muscle tension or stiffness (46). Furthermore, muscle pain develops 1 or 2 days after the exercise, which is thought to reflect increased release of noxious chemicals from damaged muscle (39). This delayed onset muscle soreness (DOMS) is not discernible at rest but is elicited under mechanical stimulation such as pressure, stretching, or contraction of the affected muscle (45), which can produce debilitating and long-lasting effects on muscle function (7).Along with these changes in the muscle, several lines of evidence suggest that eccentric muscle damage pro...

Cortical Somatosensory Excitability Is Modulated in Response to Several Days of Muscle Soreness

“…In the present study corticomotor excitability of ECR was reduced after eccentric exercise provoking DOMS and, interestingly, it was still depressed after 2 days, even though the metabolic fatigue and changes in the sarcolemmal excitability (M-wave) were presumably recovered [35,36].…”

Neuromuscular changes and the rapid adaptation following a bout of damaging eccentric exercise

“…The cSP was not affected at any time point following the eccentric exercise. In contrast, Pitman & Semmler () reported a reduction in short interval intracortical inhibition immediately following maximal eccentric exercise performed with the elbow flexors and attributed this finding to a short‐term change in afferent feedback within the muscle resulting from the damage. Thus, it is possible the eccentric muscle damage elicits changes in inhibition, but these were not identified by a change in the cSP in the present study.…”

“…However, there are lines of research that have documented changes occurring within the central nervous system (CNS) following unaccustomed, eccentric exercise (Semmler ). Specifically, following eccentric exercise, there is evidence showing reduced inhibition (Pitman & Semmler ) and a reduced voluntary activation (VA; i.e. increased central fatigue) when measured at the motor nerve (Prasartwuth et al .…”

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