Date of Completion

5-7-2020

Embargo Period

5-7-2021

Keywords

Heat Acclimation, Heat Acclimatizatization, Heat Training, Performance

Major Advisor

Douglas J .Casa

Associate Advisor

Elaine C. Lee

Associate Advisor

Lindsay J. DiStefano

Associate Advisor

Rebecca L. Stearns

Associate Advisor

Robert A. Huggins

Field of Study

Kinesiology

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

Background: Heat acclimation (HA) and heat acclimatization (HAz) are impactful strategies to mitigate negative impact of exercise performance in the heat. However, there is no practical strategy to prevent decay following HAz and HA. Purpose: The purpose of this study was to investigate the effect of HA following HAz or dual heat acclimatization (DHA) on endurance performance and the effect of heat training (HT) on endurance performance following DHA. Methods: Twenty-six endurance athletes (mean (M)±SD; age, 35±12yrs; body mass, 72.8±8.9kg; height, 178.7±6.3 cm; VO2max, 57.3±6.7ml·kg-1·min-1) completed five 4km time trials (TT) (baseline-unacclimatized, test#1; post-HAz, test#2; post-HA/DHA, test#3; 4 weeks post-DHA, test#4; 8 weeks post-DHA, test#5) in the heat (M±SD; ambient temperature [Tamb], 35.5±0.7 °C; relative humidity [%RH], 46.3±2.2%; Wet Bulb Globe Temperature (WBGT), 29.2±0.7 °C). After test#1, participants performed self-directed summer training followed by test#2. Then, they completed a five-days of a HT over eight days in the heat (M±SD; Tamb, 39.2±0.4 °C; %RH, 51.1±2.6%; WBGT, 33.2±0.7 °C). During the HA sessions, participants exercised to induce hyperthermia for 60 minutes, which is defined as hyperthermic zone HA (HZHA, 38.50°C and 39.75°C). Participants were then divided into three groups; maximal heat training group (HTMAX), minimum heat training (HTMIN), and the control group (HTCON). HTMAX completed a total of sixteen visits and HTMIN completed a total of eight visits over the course of eight weeks. The exercise used for the HT matched the HA sessions. Percent 4km time change (TTp) was calculated based on test#3 results. Results: TTp was significantly faster at test#3 compared to test#1 (M±SD; 4.8±10.1 %, p=0.024) and test#2 (M±SD; 3.1±7.4 %, p=0.040). TTp was significantly faster in HTMAX (M±SD; -4.2±5.4 %) compared to HTMIN (M±SD; 1.9±6.5 %, p=0.044) and HTcon (M±SD; 10.7±17.0 %, p=0.024) at test#5. There were no differences of TTp in HTMIN between test#3, test#4 (M±SD; 0.95±5.55%), and test#5 (M±SD; 1.93±6.45%). Conclusions: These results indicated that HT twice per week demonstrated improvement after 8 weeks following DHA, while HACON lost adaptations in 4 weeks and even greater losses in 8 weeks. HT once per week may maintain adaptations for 4 weeks and potentially for 8 weeks.

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Available for download on Friday, May 07, 2021

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