The effect of 15 consecutive days of heat-exercise acclimation on heat shock protein 70

Abstract

The purpose of this study was to investigate the alterations in serum heat shock protein (Hsp) 70 levels during a 15-consecutive-day intermittent heat-exercise protocol in a 29-year-old male ultra marathon runner. Heat acclimation, for the purpose of physical activities in elevated ambient temperatures, has numerous physiological benefits including mechanisms such as improved cardiac output, increased plasma volume and a decreased core temperature (T (c)). In addition to the central adaptations, the role of Hsp during heat acclimation has received an increasing amount of attention. The acclimation protocol applied was designed to correspond with the athlete's tapering period for the 2007 Marathon Des Sables. The subject (VO(2)max = 50.7 ml.kg(-1).min(-1), peak power output [PPO] = 376 W) cycled daily for 90 min at a workload corresponding to 50% of VO(2)max in a temperature-controlled room (average WBGT = 31.9 +/- 0.9 degrees C). Venous blood was sampled before and after each session for measurement of serum osmolality and serum Hsp70. In addition, T (c), heart rate (HR) and power output (PO) was measured throughout the 90 min to ensure that heat acclimation was achieved during the 15-day period. The results show that the subject was successfully heat acclimated as seen by the lowered HR at rest and during exercise, decreased resting and exercising T (c) and an increased PO. The heat exercise resulted in an initial increase in Hsp70 concentrations, known as thermotolerance, and the increase in Hsp70 after exercise was inversely correlated to the resting values of Hsp70 (Spearman's rank correlation = -0.81, p < 0.01). Furthermore, the 15-day heat-exercise protocol also increased the basal levels of Hsp70, a response different from that of thermotolerance. This is, as far as we are aware, the first report showing Hsp70 levels during consecutive days of intermittent heat exposure giving rise to heat acclimation. In conclusion, a relatively longer heat acclimation protocol is suggested to obtain maximum benefit of heat acclimation inclusive of both cellular and systemic adaptations.

Fig. 1

Thermoregulation response and cardiovascular adaptations over the acclimation period. HR at rest, T_c at rest and end T_c over the 15-day acclimation period

Fig. 2

Exercise performance and cardiovascular response over the 15-day acclimation period. Representative HR data from the 90-min exercise trial are shown from days 1, 5 and 15. The subject was allowed to rest every 25 min for 5 min, as indicated by the decrease in HR at 25 and 55 min. The arrows indicate when the cadence could not be maintained and the PO was decreased. The bars in the lower part of the figure show the average PO from each of the 15 days

Fig. 3

Presentation of the Hsp70 response over the 15 consecutive exercising days. The bars represent the percentage change in Hsp70 levels between resting and exercise. The line shows the resting values of Hsp70 over the 15 days

Fig. 4

The relationship between resting and change in Hsp70 concentration in response to heat exercise. It was analysed using a two-tailed Spearman’s rank correlation (R_s = −0.81, p < 0.01)