Heat Exposure for Heat Acclimation

Overseen By Normand A Richard, MSc

Age: 18 - 65

Sex: Female

Trial Phase: Academic

Sponsor: Trinity Western University

Disqualifiers: Unable to exercise, Heat intolerance, Pregnant

No Placebo Group All trial participants will receive the active study treatment (no placebo)

Compensation: Varies

Number of Visits: 19

14 Participants Needed

What You Need to Know Before You Apply

What is the purpose of this trial?

This trial examines how well people exercise in the heat after two types of heat exposure: heat acclimation alone and heat acclimation followed by maintenance. The goal is to determine if ongoing heat exposure improves the heart, blood, and body temperature's ability to handle exercise in hot conditions. The trial suits those interested in endurance sports, such as cycling, who use a smart trainer or similar equipment. As an unphased study, it offers a unique opportunity to contribute to understanding how heat exposure can enhance athletic performance.

Will I have to stop taking my current medications?

The trial information does not specify whether you need to stop taking your current medications.

What prior data suggests that heat exposure is safe for heat acclimation?

Research has shown that gradually getting used to hot conditions, known as heat acclimation, is generally safe when done properly. Studies have found that slowly increasing heat exposure over 7 to 14 days helps the body adjust without major risks. Workers who need to handle heat in their jobs have successfully used this method.

However, heat can be dangerous if not managed correctly. Following guidelines and watching for warning signs like dizziness or extreme tiredness is important. The goal is to build up tolerance without overdoing it.

Overall, when done carefully, heat acclimation is considered safe. It helps the body handle heat better without causing harm. ^{1 2 3 4 5}

Why are researchers excited about this trial?

Researchers are excited about the heat exposure technique for heat acclimation because it offers a natural and potentially more effective way to improve the body's ability to handle high temperatures. Unlike traditional methods that primarily focus on hydration and cooling strategies, this approach aims to train the body to adapt to heat through repeated controlled exposure. This could lead to enhanced endurance and performance in hot environments, making it a promising advancement for athletes and workers who regularly face extreme heat.

What evidence suggests that heat exposure is effective for heat acclimation?

Research has shown that repeated exposure to heat can enhance performance during exercise in hot weather. In this trial, participants in the Heat Acclimation arm will undergo heat acclimation sessions to test these effects. Studies have found that heat acclimation can improve performance in timed exercises and maintain those improvements with regular practice. Evidence also suggests that heat acclimation can enhance heart function, improve fluid management, and even boost cognitive skills. Additionally, it might improve performance in cooler weather, although results can vary. Overall, using heat as a treatment helps the body adjust for better performance and endurance in high temperatures. ^{3 6 7 8 9}

Who Is on the Research Team?

Anita T Coté, PhD

Principal Investigator

Trinity Western University

Are You a Good Fit for This Trial?

This trial is for females who can safely undergo heat exposure and are interested in improving their body's response to heat. Specific eligibility details are not provided, but typically participants should be healthy with no conditions that could be worsened by heat.

Inclusion Criteria

Able to speak, read, and write in English

Familiar with the sport of cycling and own a bicycle and smart trainer (or a trainer and a power meter)

Endurance athlete or currently engaging in endurance exercise

Exclusion Criteria

Unable to exercise

Pregnant

I experience discomfort or illness from heat.

Timeline for a Trial Participant

Screening

Participants are screened for eligibility to participate in the trial

2-4 weeks

Heat Acclimation

Participants undergo 10 sessions of heat acclimation over two weeks

2 weeks

10 sessions (in-person)

Heat Acclimation Maintenance

Participants undergo three weeks of heat acclimation maintenance with three heat sessions per week

3 weeks

9 sessions (in-person)

Follow-up

Participants are monitored for changes in exercise performance and physiological responses

4 weeks

What Are the Treatments Tested in This Trial?

Interventions

• Heat exposure

Trial Overview

The study tests if maintaining adaptations from repeated heat exposure (heat acclimation) benefits exercise performance in the heat more than just initial acclimation. Participants will exercise under hot conditions at three stages: before, after acclimation, and post-maintenance.

How Is the Trial Designed?

Group I: Heat Acclimation Experimental Treatment 1 Intervention

Participants in this arm will undergo heat acclimation sessions

Group II: Control Active Control 1 Intervention

Participants in this arm will undergo heart rate matched training volume

Who Is Running the Clinical Trial?

Trinity Western University

Lead Sponsor

Trials

2

Recruited

580+

Published Research Related to This Trial

Heat acclimation significantly enhances endurance and thermal comfort for workers in hot environments by improving sweating, blood flow, fluid balance, and cardiovascular stability.

For workers in personal protective suits, traditional heat acclimation methods like exercise training may be less effective due to limited sweating and increased discomfort, highlighting the need for better management of work conditions and rates.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Effectiveness of exercise-heat acclimation for preventing heat illness in the workplace. Yamazaki, F.[2019]

In a study of 13 young healthy men undergoing a heat acclimation protocol over 8 days, about 31% achieved short-term heat acclimation after just 5 days, indicating that some individuals can adapt more quickly to heat stress.

The study found significant reductions in core temperature and heart rate after 5 days of heat exposure, suggesting that even a short duration of acclimation can lead to physiological improvements, although sweat rate remained unchanged.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Individual variability in achievement of short-term heat acclimation during a fixed intensity protocol. Saillant, MM., Charkoudian, N., Salgado, RM.[2022]

A meta-analysis of studies indicates that higher heat exposure is linked to an increase in occupational injuries, particularly affecting younger workers and males, with a reported 0.5% increase in injury odds for every 1°C rise in temperature.

While the exact mechanisms behind heat exposure leading to injuries are still being explored, effective prevention strategies have yet to be established, highlighting the need for tailored approaches that consider local conditions and involve community participation.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Heat Exposure and Occupational Injuries: Review of the Literature and Implications. Spector, JT., Masuda, YJ., Wolff, NH., et al.[2023]

A study of 12,213 outdoor agricultural workers found that higher heat exposure, measured by Humidex, is associated with an increased risk of traumatic injuries, with odds ratios indicating a 14-15% higher risk at moderate to high heat levels (≥25 Humidex).

The risk of injury was particularly pronounced during cherry harvest in June and July, suggesting that specific tasks and seasonal conditions may heighten the danger for workers in warm environments.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

A Case-Crossover Study of Heat Exposure and Injury Risk in Outdoor Agricultural Workers. Spector, JT., Bonauto, DK., Sheppard, L., et al.[2022]

Heat acclimation in a hot environment (40°C) leads to greater increases in core temperature, sweating rate, and heat shock protein levels compared to overdressing in a temperate environment (15°C), indicating that true heat exposure is more effective for physiological adaptation.

While overdressing can simulate some thermoregulatory responses, it may not fully replicate the benefits of exercising in actual heat, suggesting that athletes may need to seek more effective methods for heat acclimation to optimize performance.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Physiological Responses to Overdressing and Exercise-Heat Stress in Trained Runners. Ely, BR., Blanchard, LA., Steele, JR., et al.[2019]

Exercise heat acclimation leads to significant physiological adaptations that enhance the body's ability to regulate temperature, reduce heat-related illness risk, and improve aerobic performance, especially in warm environments.

Controlled hyperthermia regimens may offer faster and more complete adaptations compared to traditional methods, and outdoor acclimation can provide specific benefits tailored to the conditions athletes will face in competition.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Adaptations and mechanisms of human heat acclimation: Applications for competitive athletes and sports. Périard, JD., Racinais, S., Sawka, MN.[2022]

In a study of 58 male navy boiler tenders exposed to extreme heat, urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels, a marker of oxidative DNA damage, significantly increased after a 7-day sailing period, indicating heat stress effects on the body.

Heat-acclimated individuals showed a significant decrease in urinary 8-OHdG levels, suggesting that acclimation may help reduce oxidative DNA damage caused by high heat exposure in occupational settings.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Heat acclimation decreased oxidative DNA damage resulting from exposure to high heat in an occupational setting. Huang, YK., Lin, CW., Chang, CC., et al.[2021]

Physical training enhances the body's ability to sweat by improving the sensitivity and activity of sweat glands, which helps with heat dissipation during thermal stress.

Heat acclimation not only improves sweat production but also lowers the thresholds for sweating, suggesting that both physical training and acclimation lead to different adaptations in the body's response to heat.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Eccrine sweat glands. Adaptations to physical training and heat acclimation. Taylor, NA.[2022]

A study of 1241 heat-related illness (HRI) claims from Washington State revealed that 76% occurred on days with temperatures above 80°F, highlighting the importance of monitoring high temperatures in occupational settings.

HRI claims were significantly more common on days with sudden temperature increases of 10°F or more, indicating that rapid temperature changes pose a higher risk for heat-related illnesses and emphasizing the need for effective heat acclimatization programs.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Occupational heat-related illness in Washington State: A descriptive study of day of illness and prior day ambient temperatures among cases and clusters, 2006-2021. Spector, JT., Sampson, L., Flunker, JC., et al.[2023]

Hot water immersion (HWI) resulted in a greater increase in tympanic temperature compared to exercise-heat acclimation (EHA), indicating a higher thermal strain during the acclimation process.

Despite the higher thermal strain from HWI, both HWI and EHA similarly reduced heart rate, core temperature, and perceived exertion, suggesting that HWI could be an effective method for improving heat tolerance without compromising cardiovascular or thermoregulatory responses.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Short-term hot water immersion results in substantial thermal strain and partial heat acclimation; comparisons with heat-exercise exposures. Greenfield, AM., Pereira, FG., Boyer, WR., et al.[2021]

Short-term heat acclimation (STHA) training, involving up to 7 heat exposures, can enhance aerobic performance in healthy adults, as shown in a systematic review of 8 studies.

The improvements in performance are likely due to cardiovascular and metabolic adaptations that help reduce fatigue and improve effort perception, although the evidence is limited and should be interpreted cautiously.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Short-term heat acclimation training improves physical performance: a systematic review, and exploration of physiological adaptations and application for team sports. Chalmers, S., Esterman, A., Eston, R., et al.[2022]

A tragic case of a 19-year-old worker who died from heat stroke after 7 hours of outdoor work highlights the severe risks of heat exposure, even for young and healthy individuals.

The study emphasizes the need for better awareness and preventive measures against heat-related illnesses in the workplace, including acclimatization, hydration, and proper training, as heat exposure is often underestimated in various common work activities.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

[Heat stroke in the workplace: description of a case with fatal outcome]. Roccatto, L., Modenese, A., Occhionero, V., et al.[2010]

Heat acclimation (HA) improved thermoregulation, perceived exertion, and exercise performance in both young and elderly participants, indicating its efficacy across age groups.

Both exercise-based heat acclimation and post-exercise hot water immersion are effective methods for preparing elderly individuals to handle heat stress, with no significant differences in outcomes between the two approaches.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Exercise heat acclimation and post-exercise hot water immersion improve resting and exercise responses to heat stress in the elderly. Waldock, KAM., Gibson, OR., Relf, RL., et al.[2021]

Citations

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pmc.ncbi.nlm.nih.gov

pmc.ncbi.nlm.nih.gov/articles/PMC9460081/

Effects of Heat Acclimatization, Heat Acclimation, and ...

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 ...

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pmc.ncbi.nlm.nih.gov

pmc.ncbi.nlm.nih.gov/articles/PMC6422510/

Application of evidence-based recommendations for heat ...

HA may also improve aerobic performance in cooler conditions up to 6% [1]. However, other investigations showed no effect [25,26].

3.

bmcsportsscimedrehabil.biomedcentral.com

bmcsportsscimedrehabil.biomedcentral.com/articles/10.1186/s13102-024-01038-6

The effect of post-exercise heat exposure (passive heat ...

“Active” heat acclimation (exercise-in-the-heat) can improve exercise performance but the efficacy of “passive” heat acclimation using post- ...

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sciencedirect.com

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Heat Acclimatization - an overview

Additionally, dry heat gain increased by ~ 6% after heat acclimation; the resulting improvement in maximal whole-body evaporative heat loss was measured to be ...

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Shifting focus: Time to look beyond the classic physiological ...

Some evidence suggests that heat acclimation improves cardiac function, body fluid regulatory functions, and preserves cognitive performance ...

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cdc.gov

cdc.gov/niosh/heat-stress/recommendations/acclimatization.html

Acclimatization | Heat

To acclimatize workers, gradually increase their exposure time in hot environmental conditions over a 7-14 day period. New workers will need ...

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osha.gov

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Overview: Working in Outdoor and Indoor Heat Environments

The process of building tolerance is called heat acclimatization. Lack of acclimatization represents a major risk factor for fatal outcomes.

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who.int

who.int/news-room/fact-sheets/detail/climate-change-heat-and-health

Heat and health

Heat stress is the leading cause of weather-related deaths and can exacerbate underlying illnesses including cardiovascular disease, diabetes, ...

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aiha.org

aiha.org/public-resources/healthierworkplaces/healthier-community-resources/thermal-heat-stress-resources-oehs-professionals

Thermal (Heat) Stress

Heat stress is the heat load to which a worker may be exposed from combined metabolic heat from physical exertion, environmental conditions, and clothing.