Brief Heat Training: No Improvement of the Lactate Threshold in Mild Conditions

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 (ie, 7-10 × 60-100 min sessions), the current article details 2 studies that aimed to determine the effect of brief (≤240 min exposure) heat training on the second lactate threshold (LT₂) in mild conditions.

Forty-one participants completed 5 (study 1, n = 18) or 4 (study 2, n = 23) perceptually regulated treadmill exercise training sessions in 35°C and 30% relative humidity (RH) (experimental group) or 19°C and 30% RH (control group). Preincremental and postincremental exercise testing occurred in mild conditions (19°C and 30% RH). Linear mixed-effects models analyzed the change in LT₂. Results Heat training did not substantially change LT₂ in either study 1 (+1.2%, d = 0.38, P = .248) or study 2 (+1.9%, d = 0.42, P = .163). LT₂ was not substantially changed in the control group in study 1 (+1.3%, d = 0.43, P = .193), but a within-group change was evident in study 2 (+2.3%, d = 1.04, P = .001).

Brief heat training was inadequate to improve the speed at LT₂ in mild conditions more than comparable training in mild conditions. The brief nature of the heattraining 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.