Influence of passive lower-body heating on muscle metabolic perturbation and high-intensity exercise tolerance in humans

• Published in: European journal of applied physiology Vol. 112; no. 10; pp. 3569 - 3576
• Main Authors: Bailey, Stephen J., Wilkerson, Daryl P., Fulford, Jonathan, Jones, Andrew M.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01.10.2012; Springer; Springer Nature B.V
• Subjects: Adenosine triphosphate; Adult; Biological and medical sciences; Biomedical and Life Sciences; Biomedicine; Body Temperature - physiology; Body Temperature Regulation - physiology; Exercise - physiology; Exercise Tolerance - physiology; Fever; Fundamental and applied biological sciences. Psychology; Heart Rate - physiology; Heat; Human Physiology; Humans; Hyperthermia; Investigations; Male; Metabolism; Metabolites; Muscle fatigue; Muscle, Skeletal - physiology; Musculoskeletal system; Occupational Medicine/Industrial Medicine; Original Article; Oxygen Consumption - physiology; Sports Medicine; Temperature; Vertebrates: body movement. Posture. Locomotion. Flight. Swimming. Physical exercise. Rest. Sports; United Kingdom > UK; Fatigue; P-MRS; Hyperthermia; Muscle metabolism; Physical exercise; Human; Intensity; Tolerance; Striated muscle; Metabolism
• ISSN: 1439-6319; 1439-6327; 1439-6327
• DOI: 10.1007/s00421-012-2336-6

The purpose of this investigation was to determine the influence of heat stress on the dynamics of muscle metabolic perturbation during high-intensity exercise. Seven healthy males completed single-legged knee-extensor exercise until the limit of tolerance on two separate occasions. In a randomized order the subjects underwent 40 min of lower-body immersion in warm water at 42°C prior to exercise (HOT) or received no prior thermal manipulation (CON). Following the intervention, muscle metabolism was measured at rest and throughout exercise using 31 P-MRS. The tolerable duration of high-intensity exercise was reduced by 36% after passive heating (CON: 474 ± 146 vs. HOT: 303 ± 76 s; P  = 0.005). Intramuscular pH was lower over the first 60 s of exercise (CON: 7.05 ± 0.02 vs. HOT: 7.00 ± 0.03; P  = 0.019) in HOT compared to CON. The rate of muscle [PCr] degradation during exercise was greater in the HOT condition (CON: −0.17 ± 0.08 vs. HOT: −0.25 ± 0.10% s −1 ; P  = 0.006) and pH also tended to change more rapidly in HOT ( P  = 0.09). Muscle [PCr] (CON: 26 ± 14 vs. HOT: 29 ± 10%), [Pi] (CON: 504 ± 236 vs. HOT: 486 ± 186%) and pH (CON: 6.84 ± 0.13 vs. HOT: 6.80 ± 0.14; P  > 0.05) were not statistically different at the limit of tolerance ( P  > 0.05 for all comparisons). These results suggest that the reduced time-to-exhaustion during high-intensity knee-extensor exercise following lower-body heating might be related, in part, to accelerated rates of change of intramuscular [PCr] and pH towards ‘critical’ values that limit muscle function.