Brief heat training : no improvement of the lactate threshold in mild conditions

Purpose: Athletes often seek the minimum required time that might elicit a physiological or performance change. It is reasonable to suggest that heat training may improve aerobic-based performance in mild conditions. Therefore, rather than providing a traditional heat exposure stimulus (i.e. 7-10 x 60-100 min sessions), the current paper details two studies that aimed to determine the effect of brief (≤240 min of exposure) heat training upon the second lactate threshold in mild conditions. Methods: Forty-one participants completed five (Study 1; n=18) or four (Study 2; n=23) perceptually-regulated treadmill exercise training sessions in 35 °C and 30% relative humidity (experimental group) or 19 °C and 30% relative humidity (control group) conditions. Pre- and post-incremental exercise testing occurred in mild conditions (19 °C and 30% relative humidity). Linear mixed effects models analysed the change in LT2. Results: Heat training did not substantially change LT2 in either Study 1 (+1.2%, d=0.38, p=0.248) or Study 2 (+1.9%, d=0.42, p=0.163). The LT2 was not substantially changed in the control group in Study 1 (+1.3%, d=0.43, p=0.193), but a within-group change was evident in Study 2 (+2.3 %, d=1.04, p=0.001). Conclusions: The studies indicated that brief heat training was inadequate to improve the speed at LT2 in mild conditions to a greater extent than comparable training in mild conditions. The brief nature of the heat training protocol did not allow adaptations to develop to the extent required to potentially confer a performance advantage in an environment that is less thermally stressful than the training conditions.