Serum S-100B Response to Moderate-Intensity Exercise-Heat Strain Before and After Acclimation

Abstract

Intense exercise alone and in combination with environmental heat stress can elevate blood S-100β protein concentrations. Moderate intensity exercise with marked environmental heat stress has not been studied, nor has the potential for heat acclimation to alter the response. PURPOSE: Determine the S-100β response to moderate intensity exercise with marked heat strain in a population vulnerable to exercise-heat exhaustion before and after acclimation. METHODS: Nine healthy male volunteers completed a heat acclimation protocol consisting of up to 100 minutes of treadmill walking (1.56m/sec, 4% grade) in the heat (45°C, 20% relative humidity) for 10 consecutive days. Changes in heart rate (HR), rectal temperature (Tre), and sweat rate (SR) were examined to determine successful acclimation. Area under the curve (AUC) for Tre> 38.5°C was calculated to assess cumulative hyperthermia. Blood samples were taken before and after exercise on days 1 and 10 and analyzed for serum osmolality and S-100β concentration. RESULTS: All subjects displayed physiological adaptations to heat acclimation, including a significant (P<0.05) reduction in final HR (161 to 145 b/min) and Tre (39.0 to 38.4°C), as well as a modest (~10%) increase in SR (1.10 to 1.20 L/hr; p=0.09). No differences were observed in pre-to-post exercise serum S-100β concentrations on day 1 or day 10, nor were differences observed in S-100β values between days 1 and 10. No significant correlations were found between S100&β values and any variable of interest. CONCLUSIONS: S-100β concentrations were not increased in response to moderate intensity exercise with marked heat strain in this study, thus no effect of heat acclimation was observed despite other classical signs of adaptation. Factors other than hyperthermia alone may better explain the rise in S-100β often observed with moderate intensity exercise to exhaustion in the heat.