title: Reduced short-interval intracortical inhibition after eccentric muscle damage in human elbow flexor muscles.
abstract: 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 ± 0.6 yr; mean ± SD) male subjects performed maximal eccentric exercise of the elbow flexor muscles until maximal voluntary contraction (MVC) force was reduced by ∼40%. 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 M-waves, 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 < 0.001), a 41% decline in resting M-wave (P = 0.01), changes in resting elbow joint angle (10°, P < 0.001), and a shift in the optimal elbow joint angle for force production (18°, P < 0.05) 2 h after exercise. This was accompanied by impaired muscle strength (27%, P < 0.001) and increased muscle soreness (P < 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.
authors: Discipline of Physiology, School of Medical Sciences, The University of Adelaide, Adelaide, Australia.
authors: Bradley M
authors: BM
authors: Pitman
authors: John G
authors: JG
authors: Semmler
mesh_terms: D000704:Analysis of Variance; D001696:Biomechanical Phenomena; D001917:Brachial Plexus / Q000503:physiopathology; D004551:Elbow Joint / Q000294:innervation*; D004558:Electric Stimulation; D004576:Electromyography; D019054:Evoked Potentials, Motor; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000503:physiopathology*; D009119:Muscle Contraction; D053580:Muscle Strength; D018482:Muscle, Skeletal / Q000294:innervation* / Q000473:pathology / Q000503:physiopathology; D009433:Neural Inhibition; D010146:Pain / Q000503:physiopathology; D010147:Pain Measurement; D016059:Range of Motion, Articular; D013997:Time Factors; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult