The effect of the rate of rise in core temperature on serum Hsp70 during exercise in the heat

Abstract

Exercise induces an increase in serum Hsp70 (sHsp70), which may modulate the innate immune response. When exercise is performed in a hot environment, heat exerts an additional stimulus to the immune system. However, we do not know if the sHSP70 is dependent on the rate of rise in core temperature (Tc). We hypothesized that sHsp70 post exercise in the heat will be smaller when the rate of rise in Tc is attenuated by applying cooling. Seven healthy male (age: 26±3years; height: 179±6cm; weight: 75.4±6.0kg; maximum oxygen uptake (VO2max): 58±8mL/kg/min) performed two identical tests in the heat (42°C, 30% rh). Subjects exercised with no cooling (no cool) and a water-perfused vest (cool) in two different trials. Subjects walked on a treadmill (~50% VO2max) in military summer fatigues, body armor, and a backpack (total gear equaled 15% of their body weight) until Tc reached 38.5°C or heart rate (HR) exceeded 95% HRmax. sHSP70 was measured pre and post exercise by ELISA. The exercise duration was longer for cool condition (88±33min) than for no cool (46±13min) (p<0.05). sHSP70 increased pre to post exercise from 0.57±0.61 to 1.69±0.66 ng/mL, in no cool (p<0.05). In the cool condition, sHSP70 changed from 0.81±1.30 to 1.70±0.67 ng/mL (p=0.08). Thus, there was no difference in post exercise sHSP70 between the two conditions (p>0.05). This suggests that sHsp70 during exercise in the heat is primarily determined by the core temperature attained rather than the rate of rise in core temperature.