Cheung, S. S., Morrison, S. A., & Sleivert, G. G. (2006). Influence of aerobic fitness on motor unit activation and isometric maximum voluntary contraction during hyperthermia. Medicine and Science in Sports and Exercise, 38(5), Supplement abstract 2053.

This study determined the role of aerobic fitness on central neuromuscular activation and maximal voluntary contractile force during hyperthermia. Healthy males (N = 37) in three distinct groups based on aerobic fitness and training history were passively heated using a liquid conditioning garment in a hot (35C, 50% RH) environment with the intention of testing neuromuscular function with whole-body hyperthermia. Of these, 11/13 highly fit, 11/13 moderately fit, 4/11 low fit Ss tolerated heating to 39.0C. Maximal force output and voluntary activation were examined during a 10-s maximal isometric knee extension.

Passive heating to a core temperature of 39.0C attenuated force production and decreased voluntary activation equally across all fitness groups in those individuals able to reach that level of hyperthermia. The ability to tolerate passive heating to 39.0C and above differed between the high and moderately fit groups when compared to the low-fitness group, despite no difference in their psychophysical rankings of thermal sensations and/or (dis)comfort.

Implication. Low aerobic fitness and activity level are associated with a decreased tolerance to passive hyperthermia. However, at high body temperatures, maximum force production and voluntary activation were impaired to an equal level regardless of training status.

Return to Table of Contents for this issue.