Pre-Cooling for Heat Stress

Overseen By Glen P Kenny, PhD

Age: 18 - 65

Sex: Male

Trial Phase: Academic

Sponsor: University of Ottawa

Disqualifiers: Chronic diseases, Acute illness, Sedentary, others

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

Compensation: Varies

Number of Visits: 2

What You Need to Know Before You Apply

What is the purpose of this trial?

This trial examines how cooling the body before exercise affects heat tolerance during workouts. It tests whether cooling off in cold water before cycling in a hot environment helps individuals exercise longer or more intensely. The study compares cycling with and without pre-cooling treatments, such as cold-water immersion or ice slurry ingestion, to observe differences. Ideal participants are healthy young men who are non-smokers and regularly engage in physical activity. As an unphased trial, this study allows participants to contribute to innovative research that could enhance exercise performance in hot conditions.

Will I have to stop taking my current medications?

The trial does not specify if you need to stop taking your current medications, but if you are using any medication that might make participation inadvisable, it could be a reason for exclusion.

What prior data suggests that pre-cooling is safe for endurance exercise in heat?

Research has shown that cold water immersion, a type of pre-cooling, safely and effectively boosts endurance in hot weather. Studies have found that this method enhances athletic performance by lowering body temperature, enabling harder and longer exercise without overheating.

Pre-cooling is generally considered safe, with minimal risk of side effects. Although most research focuses on performance benefits, there are no widespread reports of serious negative effects. Athletes and emergency workers often use cold water immersion to manage heat stress, indicating its safety for most people. ^{1 2 3 4 5}

Why are researchers excited about this trial?

Researchers are excited about the pre-cooling method for managing heat stress because it offers a proactive way to prepare the body for extreme temperatures. Unlike traditional treatments that often focus on addressing heat stress after it occurs, such as hydration and rest, pre-cooling involves cooling the body beforehand using cold-water immersion. This technique lowers the body's core temperature by about 0.5°C, potentially enhancing endurance and reducing heat-related fatigue during prolonged activities in hot conditions. By preventing heat stress before it starts, pre-cooling could provide a significant advantage for athletes and workers exposed to high heat environments.

What evidence suggests that pre-cooling might be an effective strategy for heat stress during exercise?

This trial will compare the effects of pre-cooling with no cooling on exercise performance in heat. Research has shown that cooling down before exercising, especially with cold water, can enhance performance in hot weather. Participants in the pre-cooling arm will undergo cold-water immersion, which studies have found effective in lowering core body temperature. This allows individuals to tolerate more heat and improve performance. While other methods, like drinking ice slurries, are also used, cold-water immersion is often more practical and effective in everyday situations. Overall, cooling with cold water enables longer and more intense exercise in hot conditions. ^{4 5 6 7 8}

Who Is on the Research Team?

Glen P Kenny, PhD

Principal Investigator

University of Ottawa

Are You a Good Fit for This Trial?

This trial is for individuals who can safely perform moderate-intensity cycling and are interested in how pre-cooling strategies might affect their body's heat exchange during exercise in hot conditions. Specific eligibility criteria were not provided.

Inclusion Criteria

Non-smoking

Ability to provide informed consent

Exclusion Criteria

I lead a mostly inactive lifestyle.

I have a chronic condition like high blood pressure or diabetes.

I have a physical condition that limits my activity.

Timeline for a Trial Participant

Screening

Participants are screened for eligibility to participate in the trial

2-4 weeks

Pre-Cooling

Participants undergo cold-water immersion to decrease rectal temperature by 0.5°C from baseline values before exercise

1 session

1 visit (in-person)

Exercise

Participants complete 60 minutes of continuous moderate-intensity cycling in the heat with and without pre-cooling

1 hour

1 visit (in-person)

Follow-up

Participants are monitored for thermal sensation, comfort, heart rate, and other physiological responses during and after exercise

Final 15 minutes of exercise

What Are the Treatments Tested in This Trial?

Interventions

• No Cooling
• Pre-Cooling

Trial Overview The study tests the effect of pre-cooling the body with cold-water immersion before exercising in a hot environment, compared to no cooling. It measures how this affects the body's ability to lose heat while cycling for an hour at moderate intensity.

How Is the Trial Designed?

Group I: Pre-Cooling Experimental Treatment 1 Intervention

Participants will undergo a cold-water immersion (\~17°C) to elicit a decrease in rectal temperature by 0.5°C from baseline values. Thereafter, once the target temperature is achieved, participants will complete 60 min of continuous moderate-intensity cycling (200 W/m2) in the heat (wet-bulb globe temperature of 29°C; 37.5°C and 35% relative humidity).

Group II: No Cooling Active Control 1 Intervention

Participants will complete 60 min of continuous semi-recumbent cycling at a fixed metabolic heat load (200 W/m2) in the heat (wet-bulb globe temperature of 29°C; 37.5°C and 35% relative humidity) (Control condition) without pre-cooling.

Who Is Running the Clinical Trial?

University of Ottawa

Lead Sponsor

Trials

231

Recruited

267,000+

Published Research Related to This Trial

In a study with eight male participants, both pre-exercise ice slurry ingestion and cold water immersion significantly improved submaximal running times in the heat compared to warm fluid ingestion, with running times of 52.7 minutes and 56.8 minutes respectively versus 46.7 minutes for the control.

Cold water immersion was more effective at lowering rectal temperature during exercise compared to both ice slurry ingestion and the control, suggesting it may provide better thermal regulation, although ice slurry ingestion still offers a comparable cooling effect.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Pre-cooling with ice slurry ingestion leads to similar run times to exhaustion in the heat as cold water immersion. Siegel, R., Maté, J., Watson, G., et al.[2022]

Pre-cooling before exercise has been widely studied and may enhance endurance performance, but the exact mechanisms behind this improvement are still unclear, and it has primarily been associated with endurance activities.

Post-exercise cooling methods, such as cold water immersion, are commonly used by athletes for recovery, yet there is surprisingly limited research on their effectiveness in restoring muscle function and performance after heat stress.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Cooling interventions for the protection and recovery of exercise performance from exercise-induced heat stress. Duffield, R.[2019]

Ingesting ice slurry significantly reduced heart rates and rectal temperatures in eight male participants exercising in hot conditions while wearing firefighter protective clothing, indicating a beneficial cooling effect.

The physiological strain index (PSI) was lower with ice slurry ingestion compared to tepid and cold beverages, suggesting that this method effectively mitigates physiological strain during exercise in extreme heat.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Ice Slurry Ingestion and Physiological Strain During Exercise in Non-Compensable Heat Stress. Ng, J., Wingo, JE., Bishop, PA., et al.[2018]

In a study involving 7 male recreational athletes, ingesting ice slurry during breaks in simulated tennis matches significantly reduced rectal temperature compared to cold water, indicating better thermal regulation in heat conditions.

Ice slurry ingestion also resulted in lower forehead skin temperature, heart rate, and total sweat loss, suggesting it is more effective in reducing heat strain during intense physical activity in hot environments.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Ice slurry ingestion during break times attenuates the increase of core temperature in a simulation of physical demand of match-play tennis in the heat. Naito, T., Sagayama, H., Akazawa, N., et al.[2020]

Cold water immersion (CWI) significantly improves endurance performance in hot conditions, with a moderate effect size, while also effectively lowering core temperature and perceived exertion during exercise.

In contrast, ingestion of ice slurry or crushed ice (ICE) does not show a clear benefit on performance measures, although it does increase skin and core temperature responses without affecting other physiological parameters.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Ergogenic effects of precooling with cold water immersion and ice ingestion: A meta-analysis. Choo, HC., Nosaka, K., Peiffer, JJ., et al.[2018]

A study involving 16 participants tested three different cooling vests and found that using these vests before and after exercise significantly reduced core and skin temperatures, with reductions of approximately 0.5°C for rectal temperature and 0.1-1.4°C for abdominal skin temperature.

The cooling vests also improved endurance performance, increasing running times at high intensity by up to 49 seconds, while participants reported greater satisfaction regarding their thermal comfort and skin wetness during exercise.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

A light-weight cooling vest enhances performance of athletes in the heat. Webster, J., Holland, EJ., Sleivert, G., et al.[2006]

Precooling before exercise in hot conditions significantly improves performance in intermittent and prolonged activities, with a moderate effect size of 0.73, while it negatively impacts sprint performance.

Cooling during exercise also enhances performance and capacity, showing a positive effect size of 0.76, indicating that both strategies can effectively combat heat-related impairments during physical activity.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

The effect of cooling prior to and during exercise on exercise performance and capacity in the heat: a meta-analysis. Tyler, CJ., Sunderland, C., Cheung, SS.[2022]

Ingesting an ice slurry before exercise in hot conditions modestly reduced core body temperature during the first 30 minutes of exertion compared to a control beverage, based on a study with 10 male participants.

However, this cooling effect did not last throughout the entire 45-minute exercise session, as exercise time and distance completed were similar between both beverage conditions.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

The effects of ice slurry ingestion before exertion in Wildland firefighting gear. Pryor, RR., Suyama, J., Guyette, FX., et al.[2022]

Citations

1. pmc.ncbi.nlm.nih.gov pmc.ncbi.nlm.nih.gov/articles/PMC3568721/

Pre-cooling for endurance exercise performance in the heat Current evidence indicates cold water immersion may be the most effective method of pre-cooling to improve endurance performance in hot conditions.

2. pmc.ncbi.nlm.nih.gov pmc.ncbi.nlm.nih.gov/articles/PMC5356217/

Cooling interventions for athletes: An overview of ... Cold water/ice slurry ingestion and cold water immersion are not the most effective pre-cooling strategies, but can be easily applied in field based settings.

3. sciencedirect.com sciencedirect.com/science/article/abs/pii/S0306456520305325

Ice slurry ingestion before and during exercise inhibit ... Many studies have reported that pre-exercise ice slurry ingestion improves exercise performance; however, it may increase the risk of developing heat stroke ...

4. mdpi.com mdpi.com/2072-6643/16/23/4217

Effects of Precooling on Endurance Exercise Performance ... Precooling is an effective approach to improve endurance exercise performance in the heat. External precooling is more effective in improving endurance ...

5. researchgate.net researchgate.net/publication/51845175_Pre-cooling_with_ice_slurry_ingestion_leads_to_similar_run_times_to_exhaustion_in_the_heat_as_cold_water_immersion

Pre-cooling with ice slurry ingestion leads to similar run ... The purpose of this study was to compare the effects of pre-exercise ice slurry ingestion and cold water immersion on submaximal running ...

6. pmc.ncbi.nlm.nih.gov pmc.ncbi.nlm.nih.gov/articles/PMC5790850/

Does Cold Water or Ice Slurry Ingestion During Exercise Elicit ... Cold water or ice slurry ingestion during exercise seems to be an effective and practical means to improve endurance exercise performance in the heat.

7. bmcmedicine.biomedcentral.com bmcmedicine.biomedcentral.com/articles/10.1186/1741-7015-10-166

Pre-cooling for endurance exercise performance in the heat Current evidence indicates cold water immersion may be the most effective method of pre-cooling to improve endurance performance in hot conditions.

8. nature.com nature.com/articles/s41598-025-15636-y

Effectiveness of cooling strategies for emergency personnel This systematic review and meta-analysis evaluated the effects of cooling interventions on core temperature, skin temperature, heart rate, sweat ...