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Inhibition of motor unit firing during experimental muscle pain in humans
Author(s) -
Sohn Min Kyun,
GravenNielsen Thomas,
ArendtNielsen Lars,
Svensson Peter
Publication year - 2000
Publication title -
muscle and nerve
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.025
H-Index - 145
eISSN - 1097-4598
pISSN - 0148-639X
DOI - 10.1002/1097-4598(200008)23:8<1219::aid-mus10>3.0.co;2-a
Subject(s) - isometric exercise , motor unit , masseter muscle , motor unit recruitment , nociception , medicine , electromyography , muscle contraction , threshold of pain , anesthesia , contraction (grammar) , bite force quotient , physical medicine and rehabilitation , extensor digitorum communis , stimulation , anatomy , physical therapy , orthodontics , receptor
Electromyographic activity was recorded in the masseter muscle to investigate whether the firing characteristics of single motor units (SMUs) were affected by muscle pain. Capsaicin was injected into the masseter to induce pain. The interspike interval (ISI) and recruitment threshold of SMUs were measured while subjects performed isometric contractions at 5, 7.5, 10, 15, and 20% of maximum voluntary contraction. All subjects were able to maintain a stable isometric force during pain, but the mean ISI was significantly increased without changing the recruitment threshold. In all the experimental conditions, the firing frequency increased with increasing force, and SMUs recruited at low force fired at higher rates for all force levels. These results suggest that acute stimulation of nociceptive muscle afferents inhibits SMU activity without changing recruitment order in the homonymous muscle. © 2000 John Wiley & Sons, Inc. Muscle Nerve 23: 1219–1226, 2000.