title: Neuromuscular function following prolonged intense self-paced exercise in hot climatic conditions.
abstract: Muscle weakness following constant load exercise under heat stress has been associated with hyperthermia-induced central fatigue. However, evidence of central fatigue influencing intense self-paced exercise in the heat is lacking. The purpose of this investigation was to evaluate force production capacity and central nervous system drive in skeletal muscle pre- and post-cycle ergometer exercise in hot and cool conditions. Nine trained male cyclists performed a 20-s maximal voluntary isometric contraction (MVC) prior to (control) and following a 40-km time trial in hot (35°C) and cool (20°C) conditions. MVC force production and voluntary activation of the knee extensors was evaluated via percutaneous tetanic stimulation. In the cool condition, rectal temperature increased to 39.0°C and reached 39.8°C in the heat (P < 0.01). Following exercise in the hot and cool conditions, peak force declined by ~90 and ~99 N, respectively, compared with control (P < 0.01). Mean force decreased by 15% (hot) and 14% (cool) (P < 0.01 vs. control). Voluntary activation during the post-exercise MVC declined to 93.7% (hot) and 93.9% (cool) (P < 0.05 vs. control). The post-exercise decline in voluntary activation represented ~20% of the decrease in mean force production in both conditions. Therefore, the additional increase in rectal temperature did not exacerbate the loss of force production following self-paced exercise in the heat. The impairment in force production indicates that the fatigue exhibited by the quadriceps is mainly of peripheral origin and a consequence of the prolonged contractile activity associated with exercise.
authors.affiliation: Discipline of Exercise and Sport Science, Faculty of Health Sciences, University of Sydney, 75 East Street, Lidcombe, NSW, 2141, Australia. julien.periard@sydney.edu.au
authors.forename: Julien D
authors.initials: JD
authors.lastname: Périard
authors.forename: Matthew N
authors.initials: MN
authors.lastname: Cramer
authors.forename: Phillip G
authors.initials: PG
authors.lastname: Chapman
authors.forename: Corinne
authors.initials: C
authors.lastname: Caillaud
authors.forename: Martin W
authors.initials: MW
authors.lastname: Thompson
mesh_terms: D000328:Adult; D001642:Bicycling / Q000502:physiology; D002980:Climate; D004558:Electric Stimulation; D004576:Electromyography; D015444:Exercise / Q000502:physiology*; D018882:Heat Stress Disorders / Q000503:physiopathology; D006358:Hot Temperature / Q000009:adverse effects; D006801:Humans; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D009469:Neuromuscular Junction / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology; D013997:Time Factors