The efficacy of weekly and bi-weekly heat training to maintain the physiological benefits of heat acclimation

Abstract

Objectives: To examine the efficacy of weekly and bi-weekly heat training to maintain heat acclimatization (HAz) and heat acclimation (HA) for 8 weeks in aerobically trained athletes.

Design: Randomized, between-group.

Methods: Twenty-four males (mean [m ± standard deviation [sd]; (age, 34 ± 12 y; body mass, 72.6 ± 8.8 kg, VO_2peak, 57.7 ± 6.8 mL·kg^-1·min^-1) completed five trials (baseline, following HAz, following HA (HAz + HA), four weeks into heat training [HT_WK4], and eight weeks into HT [HT_WK8] that involved 60 min of steady-state exercise (59.1 ± 1.8% vVO_2peak) in an environmental laboratory (wet bulb globe temperature [WBGT], 29.6 ± 1.4 °C) on a motorized treadmill. Throughout exercise, heart rate (HR) and rectal temperature (T_rec) were recorded. Following HAz + HA, participants were assigned to three groups: control group (HT₀), once per week heat training (HT₁), and twice per week heat training (HT₂). HT involved heated exercise (WBGT, 33.3 ± 1.3 °C) to achieve hyperthermia (38.5-39.75 °C) for 60 min. Repeated measures ANOVAs were used to determine differences.

Results: HAz + HA resulted in significant improvements in HR (p < 0.001) and T_rec (p < 0.001). At HT_WK8, HR was significantly higher in HT₀ (174 ± 22 beats⋅min^-1) compared to HT₂ (151 ± 17 beats⋅min^-1, p < 0.023), but was not different than HT₁ (159 ± 17 beats⋅min^-1, p = 0.112). There was no difference in % change of T_rec from post-HAz + HA to HT_WK4 (0.6 ± 1.3%; p = 0.218), however, HT_WK8 (1.8 ± 1.4%) was significantly greater than post-HAz + HA in HT₀ (p = 0.009).

Conclusions: Bi-weekly HT provided clear evidence for the ability to maintain physiological adaptions for 8 weeks following HA.

Keywords: Adaptation; Aerobic performance; Endurance; Thermoregulation.