Effect of Heat Acclimatization, Heat Acclimation, and Intermittent Heat Training on Maximal Oxygen Uptake

Ryan A Dunn; Lauren A Fry; Yasuki Sekiguchi; Courteney L Benjamin; Ciara N Manning; Robert A Huggins; Rebecca L Stearns; Douglas J Casa

doi:10.1177/19417381241249470

Effect of Heat Acclimatization, Heat Acclimation, and Intermittent Heat Training on Maximal Oxygen Uptake

Sports Health. 2024 May 6:19417381241249470. doi: 10.1177/19417381241249470. Online ahead of print.

Authors

Ryan A Dunn¹, Lauren A Fry², Yasuki Sekiguchi³, Courteney L Benjamin⁴, Ciara N Manning², Robert A Huggins², Rebecca L Stearns², Douglas J Casa²

Affiliations

¹ Sports Performance Laboratory, Department of Kinesiology and Sport Management, Texas Tech University, Lubbock, Texas.
² Korey Stringer Institute, Department of Kinesiology, University of Connecticut, Storrs, Connecticut.
³ Sports Performance Laboratory, Department of Kinesiology and Sport Management, Texas Tech University, Lubbock, Texas and Korey Stringer Institute, Department of Kinesiology, University of Connecticut, Storrs, Connecticut.
⁴ Korey Stringer Institute, Department of Kinesiology, University of Connecticut, Storrs, Connecticut and Department of Kinesiology, Samford University, Birmingham, Alabama.

PMID: 38708678
DOI: 10.1177/19417381241249470

Abstract

Background: Maximal oxygen uptake (VO_2max) is an important determinant of endurance performance. Heat acclimation/acclimatization (HA/HAz) elicits improvements in endurance performance. Upon heat exposure reduction, intermittent heat training (IHT) may alleviate HA/HAz adaptation decay; however, corresponding VO_2max responses are unknown.

Hypothesis: VO_2max is maintained after HAz/HA; IHT mitigates decrements in aerobic power after HAz/HA.

Study design: Interventional study.

Level of evidence: Level 3.

Methods: A total of 27 male endurance runners (mean ± SD; age, 36 ± 12 years; body mass, 73.03 ± 8.97 kg; height, 178.81 ± 6.39 cm) completed VO_2max testing at 5 timepoints; baseline, post-HAz, post-HA, and weeks 4 and 8 of IHT (IHT₄, IHT₈). After baseline testing, participants completed HAz, preceded by 5 days of HA involving exercise to induce hyperthermia for 60 minutes in the heat (ambient temperature, 39.13 ± 1.37°C; relative humidity, 51.08 ± 8.42%). Participants were assigned randomly to 1 of 3 IHT groups: once-weekly, twice-weekly, or no IHT. Differences in VO_2max, velocity at VO_2max (vVO₂), and maximal heart rate (HR_max) at all 5 timepoints were analyzed using repeated-measure analyses of variance with Bonferroni corrections post hoc.

Results: No significant VO_2max or vVO₂ differences were observed between baseline, post-HAz, or post-HA (P = 0.36 and P = 0.09, respectively). No significant group or time effects were identified for VO_2max or vVO₂ at post-HA, IHT₄, and IHT₈ (P = 0.67 and P = 0.21, respectively). Significant HR_max differences were observed between baseline and post-HA tests (P < 0.01). No significant group or time HR_max differences shown for post-HA, IHT₄, and IHT₈ (P = 0.59).

Conclusion: VO_2max was not reduced among endurance runners after HA/HAz and IHT potentially due to participants' similar aerobic training status and high aerobic fitness levels.

Clinical relevance: HAz/HA and IHT maintain aerobic power in endurance runners, with HAz/HA procuring reductions in HR_max.

Keywords: aerobic exercise; athletic performance; decay; environmental stress; thermoregulation.