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

10 Participants Needed

Trial Summary

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 data supports the effectiveness of the treatment Pre-Cooling for Heat Stress?

Research shows that pre-cooling methods like cold water immersion and ice slurry ingestion can help improve exercise performance in hot conditions by lowering body temperature and reducing heat stress. These methods are particularly effective for endurance activities, although they may not benefit sprint performance. ^{1 2 3 4 5}

Is pre-cooling with ice slurry ingestion safe for humans?

Research on ice slurry ingestion for pre-cooling shows it can help manage body temperature during exercise in hot conditions, with no significant safety concerns reported in the studies reviewed. ^{2 3 4 6 7}

How does the pre-cooling treatment for heat stress differ from other treatments?

Pre-cooling treatment, which includes methods like ice slurry ingestion and cold water immersion, is unique because it helps lower body temperature before exercise, enhancing endurance and reducing heat strain. Unlike other treatments, it is applied before physical activity and can be as effective as cold water immersion, offering a practical and low-cost option for managing heat stress. ^{2 3 4 6 8}

What is the purpose of this trial?

Endurance exercise performance declines in hot environments as core body temperature increases. To enhance performance, body pre-cooling strategies, such as cold-water immersion have been employed to lower resting core temperature thereby increasing the body's heat storage capacity. In turn, the increase in body core temperature associated with exercise in the heat is blunted, allowing the individual to exercise at higher intensity and or for a longer period of time. However, the mechanisms by which pre-cooling impacts heat exchange during exercise remain unclear. While existing research has focused on the performance benefits of pre-cooling the body, relatively little is known about the impacts of pre-cooling on whole-body heat exchange during an exercise-heat stress. Investigators will therefore evaluate whole-body heat exchange (dry ± evaporative heat loss as assessed using a direct air calorimeter) during a prolonged (1-hour) moderate-intensity cycling bout in the heat (wet-bulb globe temperature of 29°C; equivalent to 37.5°C, 35% relative humidity) performed with and without pre-cooling by cool-water (\~17°C) immersion.

Research Team

Glen P Kenny, PhD

Principal Investigator

University of Ottawa

Eligibility Criteria

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

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

Treatment Details

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.

Participant Groups

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+

Findings from Research

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]

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]

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]

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]

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]

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]

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]

References

1. Switzerland pubmed.ncbi.nlm.nih.gov

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

2. United States pubmed.ncbi.nlm.nih.gov

Ice Slurry Ingestion and Physiological Strain During Exercise in Non-Compensable Heat Stress. [2018]

3. England pubmed.ncbi.nlm.nih.gov

Ergogenic effects of precooling with cold water immersion and ice ingestion: A meta-analysis. [2018]

4. England pubmed.ncbi.nlm.nih.gov

The effects of ice slurry ingestion before exertion in Wildland firefighting gear. [2022]

5. England 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. [2022]

6. England 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. [2022]

7. United States 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. [2020]

8. England pubmed.ncbi.nlm.nih.gov

A light-weight cooling vest enhances performance of athletes in the heat. [2006]