Effects of Heat Acclimatization, Heat Acclimation, and Intermittent Exercise Heat Training on Time-Trial Performance

Abstract

Background: The purpose of this study was to investigate effects of heat acclimatization (HAz) followed by heat acclimation (HA), and intermittent heat training (IHT) on time-trial performance. Hypothesis: Time-trial performance will improve after HA and will further improve with twice a week of IHT. Study Design: Interventional study. Level of Evidence: Level 3. Methods: A total of 26 male athletes (mean ± SD; age, 35 ± 12 years; body mass, 72.8 ± 8.9 kg; peak oxygen consumption [VO2peak], 57.3 ± 6.7 mL·kg−1·min−1) completed five 4-km time trials (baseline, post-HAz, post-HA, post-IHT4, post-IHT8) in the heat (ambient temperature, 35.4°C ± 0.3°C; relative humidity, 46.7% ± 1.2%) on a motorized treadmill. After baseline time trial, participants performed HAz (109 ± 10 days) followed by post-HAz time trial. Then, participants completed 5 days of HA, which involved exercising to induce hyperthermia (38.50°C-39.75°C) for 60 minutes. Participants were then divided into 3 groups and completed IHT either twice per week (IHTMAX), once per week (IHTMIN), or not at all (IHTCON) over an 8-week period. The exercise used for the IHT matched the HA. Four-kilometer time trials were performed after 4 weeks (post-IHT4) and 8 weeks of IHT (post-IHT8). Results: Time trial was faster in post-HA (17.98 ± 2.51 minutes) compared with baseline (18.61 ± 3.06 minutes; P = 0.037) and post-HAz (18.66 ± 3.12 minutes; P = 0.023). Percentage change in time trial was faster in IHTMAX (−3.9% ± 5.2%) compared with IHTCON (11.5% ± 16.9%) ( P = 0.020) and approached statistical significance with large effect (effect size = 0.96) compared with IHTMIN (1.6% ± 6.2%; P = 0.059) at post-IHT8. Additionally, IHTMAX (−2.2% ± 4.2%) was faster than IHTCON (3.6% ± 6.9%) ( P = 0.05) at post-IHT4. Conclusion: These results indicate that HA after HAz induces additional improvement in time-trial performance. IHT twice per week shows improvement after 8 weeks, while once per week maintains performance for 8 weeks. No IHT results in a loss of adaptations after 4 weeks and even greater losses after 8 weeks. Clinical Relevance: HA after HAz improves time-trial performance, twice a week of IHT improves performance further, and once a week of IHT maintains performance for at least 8 weeks.

Using Predictive Modeling Technique to Assess Core Temperature Adaptations from Heart Rate, Sweat Rate, and Thermal Sensation in Heat Acclimatization and Heat Acclimation

“…The sweat rate was significantly higher post-HA (1.93 ± 0.46 L⋅h −1 ) compared to post-HAz (1.76 ± 0.43 L⋅h −1 , p = 0.027). Detailed data and analyses during HAz, and HA as well as at baseline, post-HAz, and post-HA trials are provided in another manuscript [ 12 , 13 ].…”

“…Following an explanation of study procedures, which were approved by the Institutional Review Board (IRB) at The University of Connecticut, participants provided informed written consent to participate in this study. This study is a part of a large research study, and other research questions are answered in other manuscripts [ 12 , 13 , 14 , 15 , 16 ].…”

“…Training metrics, such as distance covered and HR, and environmental conditions for each training session were monitored. Detailed information was provided in other manuscripts [ 12 , 13 ]. After self-directed summer training, a post-HAz trial was performed to examine adaptations following HAz.…”

The Type of Per-Cooling Strategies Currently Employed by Competitive and Professional Cyclists-Triathletes During Training and Competition Are Condition (Dry vs. Humid) Dependant

“…Heat acclimation/acclimatisation is a chronic heat mitigation strategy in which the aim is to induce heat adaption and enhance an individual's ability to tolerate heat stress (Gibson et al, 2020 ). The adaptation from this strategy can be maintained for ~8weeks with intermittent heat training once a week (Sekiguchi et al, 2021 ). However, no intermittent heat training following heat acclimation/acclimatisation will result in a loss of adaptations after 4 weeks and even greater losses after 8 weeks (Sekiguchi et al, 2021 ).…”

“…The adaptation from this strategy can be maintained for ~8weeks with intermittent heat training once a week (Sekiguchi et al, 2021 ). However, no intermittent heat training following heat acclimation/acclimatisation will result in a loss of adaptations after 4 weeks and even greater losses after 8 weeks (Sekiguchi et al, 2021 ). Due to the length, nature, and cost of this strategy, some athletes opt for acute heat mitigation strategies, such as cooling and/or hydration that can be applied easily and cost-effectively during training and/or competition (Gibson et al, 2020 ).…”