The effect of exercise induced hyperthermia on muscle fibre conduction velocity during sustained isometric contraction

Citation

Hunter A, Albertus-Kajee Y & Gibson ASC (2011) The effect of exercise induced hyperthermia on muscle fibre conduction velocity during sustained isometric contraction. Journal of Electromyography and Kinesiology, 21 (5), pp. 834-840. http://www.scopus.com/inward/record.url?partnerID=yv4JPVwI&eid=2-s2.0-80052367637&md5=b664015e3a682bdcfa9a7d8a92ad73c3; https://doi.org/10.1016/j.jelekin.2011.06.002

Abstract
This study investigated the effect of dynamic exercise in a hot environment on muscle fibre conduction velocity (MFCV) of the knee extensors during a sustained isometric contraction. Seven trained male cyclists (mean [±SD], age, and V_ O2max were 35 ± 9.9 and 57.4 ± 6.6 ml kg1 min1) cycled for 50 min at 60% of peak power output in either: (1) 40 C (HOT); or (2) 19 C (NEUTRO); and (3) remained passive in 40 C (PASS). Post-intervention a 100 s maximal sustained isometric contraction (SMC) of the knee extensors was performed. Rectal temperature increased (p < 0.01) for both HOT and NEUTRO with PASS unchanged and with HOT rising higher (p < 0.01) than NEUTRO (38.6 ± 0.4 vs. 37.6 ± 0.4 C). Muscle temperature increased (p < 0.01) for all three conditions with HOT rising the highest (p < 0.01) (40.3 ± 0.5 vs. 38.3 ± 0.3 and 37.6 ± 1.3 C for NEUTRO and PASS, respectively). Lactate showed higher accumulation (p < 0.01) for HOT than NEUTRO (6.9 ± 2.3 vs. 4.2 ± 2.1 mmol l1). During SMC the torque, electromyography root mean squared (RMS) and MFCV all significantly (p < 0.01) declined. Only in HOT did MFCV decline significantly (p < 0.01) less than torque and RMS (9.9 ± 6.2% vs. 37.5 ± 17.8% and 37.6 ± 21.4%, respectively). In conclusion, during exercise induced hyperthermia, reduced motor unit recruitment as opposed to slower conducting properties of the muscle fibre appears to be responsible for the greater reduction in torque output.

Keywords
Muscle fibre conduction velocity; EMG; RMS; Hyperthermia; Sustained isometric contraction

Journal
Journal of Electromyography and Kinesiology: Volume 21, Issue 5

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