Impaired Heat Adaptation From Combined Heat Training and Live High-Train Low Hypoxia.

PURPOSE:: To determine whether combining training in heat with 'Live High, Train Low' hypoxia (LHTL) further improves thermoregulatory and cardiovascular responses to a heat tolerance test compared to independent heat training.

METHODS:: Twenty-five trained runners (VO2peak = 64.1 ±8.0 ml·min·kg-1 ) completed three-weeks training in one of three conditions: 1) Heat training combined with LHTL (H+H; FiO2 =14.4% (3000 m), 13 h·day-1 ; train at <600 m, 33°C, 55% RH); 2) heat training (HOT; live and train <600 m, 33°C, 55% RH); 3) temperate training (CONT; live and train <600 m, 13°C, 55% RH). Heat adaptations were determined from a 45 min heat response test (33°C, 55% RH, 65% vVO2peak ) at baseline, immediately, one and three weeks' post exposure (Baseline, Post, 1wkP and 3wkP, respectively). Core temperature, heart rate, sweat rate and sodium concentration, plasma volume, and perceptual responses were analysed using magnitude based inferences.

RESULTS:: Submaximal heart rate (ES= -0.60(-0.89; -0.32)) and core temperature [ES= -0.55(-0.99; -0.10)] were reduced in HOT until 1wkP. Sweat rate [ES= 0.36(0.12; 0.59)] and sweat sodium concentration [ES= -0.82(-1.48; -0.16)] were respectively increased and decreased until 3wkP in HOT. Submaximal heart rate [ES= -0.38 (-0.85; 0.08)] was likely reduced in H+H at 3wkP, whilst CONT had unclear physiological changes. Perceived exertion and thermal sensation were reduced across all groups.

CONCLUSIONS:: Despite greater physiological stress from combined heat training and LHTL, thermoregulatory adaptations are limited in comparison to independent heat training. The combined stimuli provides no additional physiological benefit during exercise in hot environments.