Hyperthermia

Critical Internal Temperature Hypothesis

This is a hypothesis that really re-emerged in the late 1990's, with studies demonstrating that humans appeared to reach voluntary exhaustion at consistent core temperatures. This occurred despite different starting core temperatures or rates of heat storage (Gonzalez-Alonso et al. 1998). Interesting, one of my Ph.D. papers also found a significant difference in final core temperature at voluntary fatigue between moderately and highly fit subjects. Overall, the CIT hypothesis suggests that elevated core temperature has a direct effect on fatigue. Research in our lab has focused on hyperthermia effects on neuromuscular function, and the respective roles of core versus skin temperature. This work is partnered with Gordon Sleivert, Ph.D. of PacificSport in Victoria and formerly the Faculty of Kinesiology at U. New Brunswick.

Cheung, S.S. Hyperthermia and voluntary exhaustion: integrating models and future challenges. Appl. Physiol. Nutr. Metab. (In Press)

Cheung, S.S. Neuropsychological determinants of exercise tolerance in the heat. Prog. Brain Res. (In Press).

Thomas, M.M.*, S.S. Cheung, G.C. Elder, and G.G. Sleivert. Voluntary muscle activation is impaired by central hyperthermia independent of local muscle temperature. J. Appl. Physiol. 100:1361-1369, 2006. PDF

Cheung, S.S. and G.G. Sleivert. Multiple triggers of hyperthermic fatigue. Exerc. Sport Sci. Rev. 32:100-106, 2004. PDF

Morrison, S.A.*, G.G. Sleivert, and S.S. Cheung. Passive hyperthermia reduces voluntary activation and isometric force production. Eur. J. Appl. Physiol. 91:729-736, 2004. PDF

Cheung, S.S. and G.G. Sleivert. Skin temperature decreases isokinetic maximal force production independent of core temperature. Eur. J. Appl. Physiol. 91:723-738, 2004. PDF

Pre-cooling as an Ergogenic Aid

Given the importance of core temperature on eliciting fatigue, it becomes logical that we want to minimise core temperature increases as much as possible during exercise in both thermoneutral and hot environments. Especially in competitions in hot environments like Athens 2004 Olympics, keeping cool can become an important advantage for competitors. Gord Sleivert from PacificSport and I are very interested in pre-cooling from both a fundamental and applied perspective. How much pre-cooling is beneficial? What type of pre-cooling is easiest to apply in real-life? Are there benefits for short, power-based events? Are there target sites like the head or torso? We have a series of upcoming studies investigating these questions.

Cheung, S.S. and A.M. Robinson†. Wingate sprinting performance in temperate environments after upper body pre-cooling. J. Sport Sci. 22:605-612, 2004. PDF

Uncompensable Heat Stress and Microclimate Cooling

My doctoral research focused on the thermophysiology of individuals wearing protective clothing during exercise in the heat. This is an incredibly challenging environment, due to the relatively impermeable clothing preventing heat dissipation and therefore producing a huge buildup of heat. This makes it fundamentally different from much of the existing research based on athletic scenarios of minimal clothing. Our research was driven by the use of chemical warfare clothing by soldiers in the Persian Gulf in the early 1990's, but it's also highly relevant to many other occupational (e.g., firefighters, hazardous disposal) and athletic (e.g., American football) settings. We focused on the separate and combined effects of exercise intensity, hydration, fitness, and heat acclimation in this environment. A continuing extension of this work is on designing cooling strategies underneath the clothing. I am also partnered with DRDC-Toronto on a pending research grant with CIHR to further research the effects of exertional heat illness on immunological and cognitive responses.

Flouris, A.D.* and S.S. Cheung. Design and control optimization of microclimate cooling systems underneath protective clothing. Ann. Biomed. Eng. PDF.

Thornley, L.J.*, S.S. Cheung, and G.G. Sleivert. Responsiveness of thermal sensors to non-uniform thermal environments and exercise. Aviat. Space Environ. Med. 74:1135-1141, 2003. PDF

McLellan, T.M. and S.S. Cheung. Impact of fluid replacement on heat storage while wearing protective clothing. Ergonomics. 43: 2020-2030, 2000. PDF

Cheung, S.S., T.M. McLellan, and S. Tenaglia. The thermophysiology of uncompensable heat stress: physiological manipulations and individual characteristics. Sports Med. 29: 329-359, 2000. PDF

McLellan, T.M., S.S. Cheung, W.A. Latzka, M.N. Sawka, K.B. Pandolf, C.E. Millard, and W.R. Withey. Effects of dehydration, hypohydration and hyperhydration on tolerance during uncompensable heat stress. Can. J. Appl. Physiol. 24: 349-361, 1999. PDF

Cheung, S.S. and T.M. McLellan. Comparison of short-term aerobic training and high maximal aerobic power on tolerance to uncompensable heat stress. Aviat. Space Environ. Med. 70: 637-643, 1999. PDF

Cheung, S.S. and T.M. McLellan. Influence of heat acclimation, aerobic fitness, and hydration status on tolerance during uncompensable heat stress. J. Appl. Physiol. 84: 1731-1739, 1998. PDF

Cheung, S.S. and T.M. McLellan. Influence of hydration status and short-term aerobic training on tolerance during uncompensable heat stress. Eur. J. Appl. Physiol. 78: 50-58, 1998. PDF

Cheung, S.S. and T.M. McLellan. Influence of hydration status and fluid replacement on heat tolerance while wearing NBC protective clothing. Eur. J. Appl. Physiol. 77: 139-148, 1998. PDF

McLellan, T.M., J.I. Pope, J.B. Cain, and S.S. Cheung. Effects of metabolic rate and ambient vapour pressure on heat strain in protective clothing. Eur. J. Appl. Physiol. 74: 518-527, 1996. PDF

Last Updated March 18, 2006

Site maintained by Dr. Stephen S. Cheung, Ph.D., Associate Professor, Dalhousie University.