Serum S-100β response to exercise-heat strain before and after acclimation

Exercise alone or in combination with environmental heat stress can elevate blood S-100β protein concentrations. However, the explanatory power of exercise with marked environmental heat stress on the appearance of S-100β is questionable. It is possible that the process of heat acclimation might afford additional insight. Purpose: Determine the S-100β response to moderate-intensity exercise with heat strain before and after heat acclimation. Methods: Nine healthy male volunteers completed 10 consecutive days of heat acclimation consisting of up to 100 min of treadmill walking (1.56 m·s ^-1, 4% grade) in the heat (45°C, 20% relative humidity). Changes in HR, rectal temperature (T _re), and sweat rate (SR) were examined to determine successful acclimation. Area under the curve (AUC) for T _re greater than 38.5°C was calculated to assess cumulative hyperthermia. Blood samples were taken before and after exercise on days 1 and 10 and were analyzed for serum osmolality and S-100β concentration. Results: All subjects displayed physiological adaptations to heat acclimation including a significant (P β 0.05) reduction in final HR (161 to 145 bpm) and T _re (39.0 to 38.4°C), as well as a modest (∼10%) increase in SR (1.10 to 1.20 L·h ^-1; P = 0.09). No differences were observed in pre- to postexercise serum S-100β concentrations on day 1 or 10, and no differences were observed in S-100β values between days 1 and 10. No significant correlations were found between S-100β values and any variable of interest. Conclusions: S-100β concentrations do not necessarily increase in response to exercise-heat strain, and no effect of heat acclimation on S-100β could be observed despite other quantifiable physiological adaptations.