Improved Athletic Performance with Precooling

Ask any athlete if they would like to improve their sport performance and they'll say, "yes!" That's why they hired you. Well, what if I told you a dip in a cold tub could be the difference between winning and losing? Or that drinking an icy sports drink, or wearing a frozen vest, could give your clients the upper hand? Precooling is a simple strategy that could have benefits to athletes in football, soccer, baseball, and softball. Athletes who compete in endurance sports—cycling, running, triathlons, etc.—could also benefit. But does it work?

The Issue: Heat and Reduced Athletic Performance

Late spring and summer sporting events are hot! During American football preseason, athletes may find themselves practicing in temperatures well over 90 degrees Fahrenheit. It's during this time, when temperature and humidity are high, that the frequency of heat-related illnesses increases.

Athletes exercising in too hot conditions are susceptible to heat stress. The longer an athlete exercises, the greater their risk for heat cramps, heat stress, or heatstroke. The same is true when exercise intensity increases.

What Are Common Heat-Related Illnesses?

Roughly 400 deaths per year result from untreated heat injuries. For athletes, exertional heat stroke is the third leading cause of death.

Common heat-related illnesses seen at endurance and other sport events include:

• Heat edema

• Heat rash

• Heat syncope

• Heat cramps

• Heat exhaustion

• Heatstroke

Science has been looking at the impact of temperature on sport performance. More specifically, they've been asking, "what is the best temperature for optimal performance?"

For example, one study we reviewed found the best environmental temperature for marathon runners is 43.16 degrees Fahrenheit for men and 44.24 degrees Fahrenheit for women. That may sound chilly, but at a temperature of 80 degrees, men's running performance decreased by 17.7%. At the same temperature, women's performance declined by 12.5%.

When it comes to cycling, the results are similar. One study found power output was higher for cyclists between 62.6 degrees and 80.6 degrees than at 98.6 degrees (the temperature of the human body).

These are both endurance events. Many marathons and bike races last in excess of three hours. How do athletes in more non-linear aerobic endurance events fare?

Not well, unfortunately.

Perhaps the worst outcomes are for football players. The five-year span between 2005 and 2009 included "the greatest number of heat-related deaths in high school and collegiate sports for any five-year period over the previous 35 years." That's a sad statistic, especially considering that heat-induced illness is completely preventable.

When are Athletes at The Greatest Risk of Heat-Related Illness?

In football, heat illness is greatest during the first seven days of preseason practice. However, injuries continue throughout the first three weeks of sports practice.

Most injuries occurred at temperatures of 82 degrees or higher.

Heat impairs exercise and sport performance. As we've mentioned, it can even be life-threatening for athletes playing summer sports such as football, soccer, rugby, baseball, and softball.

What are Causes of Decreased Performance in Extreme Heat?

The human body can tolerate large variations in environmental temperatures. Our body keeps a fairly constant core temperature even in extreme heat or cold. But exercise in extreme temps shifts the balance and the effects can be dangerous.

A combination of factors affects thermoregulation during exercise in the heat. The intensity and duration of exercise are two factors. Others to consider are more specific to the athlete and include:

• Training status

• Heat acclimatization

• Hydration status

There have been many hypotheses about why the body essentially "shuts down" during exercise in extreme heat.

Circulatory Failure

Until recently, circulatory failure—reduced cardiac output, stroke volume, arterial pressure, and blood flow to the brain, skin, and muscles—was suspected to affect performance.

However, recent research has found evidence to challenge this assumption.

In one study, researchers followed athletes for 12 days. The athletes exercised at 60% VO2Max in 104-degree heat. Exhaustion occurred at a core temperature of 103.46 degrees. When they measured cardiac output at exhaustion, there had been no reduction in output.

Decreased Substrate Availability

Another proposed culprit for reduced exercise ability during hot summer sports has to do with how our body makes energy. During exercise in the heat the rate of muscle glycogen used for energy increases. This leads many to believe that a decrease in muscle glycogen availability was to blame for fatigue.

However, researchers tested cyclists at 70% VO2Max in 91.4-degree heat. During the test, the cyclists ingested carbohydrates to prevent a dip in available glycogen. The effects shouldn't surprise you. Blood glucose levels did not fall below resting levels during the trial.

Also, there was no increase in performance or power output. The researchers concluded that fatigue was due to thermoregulatory factors, not decreased energy substrate availability.

Elevated Body Temperature

It seems that the critical limiting factor in athletic performance in hot conditions is core body temperature. There are many factors which raise the core body temperature during exercise:

• Muscle and skin blood flow

• Aerobic capacity

• Early onset of the anaerobic threshold

• Stimulation and accumulation of stress hormones

• Increased anaerobic glycolysis

• Increased use of muscle glycogen

• Lactate accumulation

If it is true that core body temperature is the key limiting factor, then keeping the body cool should help. That is why precooling has become a hot topic in recent years.

What is Precooling?

Precooling is a method of cooling the body prior to sports participation. The goal of precooling is to lower the core body temperature to increase the margin between the initial core temperature and the critical limiting temperature (103.46 degrees in some studies). Increasing this margin is supposed to increase the time it takes to reach fatigue.

Precooling produces effects similar to acclimation, which we'll discuss in a moment. First, let's review the ways the body releases heat to keep a constant 98.6 degrees.

How Does the Body Get Rid of Excess Heat?

There are four ways the body cools itself:

• Conduction: a direct transfer of excess heat during contact with a cooler object

• Convection: the air surrounding the body is cooled by the passing of cool air over exposed skin

• Evaporation: heat is released via sweat - this is the body's most effective way to release heat

• Radiation: a direct release of heat from a body into the environment

When it comes to sports, mother nature can throw some curveballs of her own that inhibit the body's ability to transfer heat. If there is no breeze, or if the circulating heat is very hot, convection will not effectively cool the body.

Heart rate increases by about ten beats per minute for every one-degree increase in core temp. In fact, the heart circulates about 2-4 times more blood on a hot day than a cool day. Blood flow to the skin uses radiation to cool the body. But radiation doesn't work very well when environmental temps are greater than body temperature.

That's where precooling—cold water immersion, ice slushy ingestion, and cooling garments—comes into play.

A Systematic Review of the Methods of Precooling

Cold water immersion is one method of precooling. Of course, this method may sound familiar because many athletes use it as a form of recovery. We've discussed using ice and heat for injury in this article.

Another precooling method for reducing core temperature is to ingest an ice slurry or slushy. Finally, the review paper we used for this article looked at cooling garments—vests and jackets packed with ice or other cooling agents.

Here is a summary of the data from this review paper:

Is Athletic Performance Improved with Precooling?

The physiological response to heat stress is quite complex. Are precooling technologies better than our natural responses to training and acclimation? In a word, no.

Cold Water Immersion: It seems that cold water immersion is the most effective method of precooling. However, it is also highly impractical on the sports field.

First, the process must be closely watched. In many trials, precooling using cold water immersion took up to 60 minutes or more to get the core temperature low enough. The process must be slow to prevent cold stress responses such as shivering. This would be prohibitive before sporting events.

Second, cold water immersion is expensive. An athlete must be nearly submerged to benefit from the effects of cold water immersion. Therefore, a large tub is necessary and lots of water, not to mention staff to check the athlete. If more than one athlete needs to take a dip, then the costs increase dramatically.

Ice Slurry Ingestion: Drinking a sports drink slushy is more cost effective than cold water immersion. It is also much more practical. Partially frozen sports drinks are easy to transport to the sports field. Research has found that just 6.8 g to 14 g of liquid per kg of body mass can help the athlete.

It is also possible for athletes to conduct warm-up exercises while precooling. Of course, this is valuable prior to competition as it saves time and serves dual purposes.

However, some studies have recorded significantly higher core temperatures at exhaustion than without the icy drink. Researchers think this effect may be due to generation of higher metabolic heat loads, an altered feeling of effort, and increased time to exhaustion. Regardless of the causes, a significantly higher core temperature is dangerous.

Cooling Garments: Current evidence suggests cooling garments just don't work. However, these are different from the moisture-wicking garments we've previously discussed in our Dress for Success article. What studies on cooling garments have found is that the skin temperature is affected, but not core body temperature.

Another study found that the cooling jacket stimulated vasoconstriction (shrinking of the surface blood vessels), preventing the transfer of heat between the skin and the cooling garment. In this case, the garment would be effectively trapping heat.

Ice-packed vests were tested during the 1996 Atlanta Olympic games. In Athens (2004) and Beijing (2008) Nike sent cooling ice vest to athletes. One of the athletes who used the Nike ice vest, pulled off a Silver medal win. The Olympic athletes who used precooling vests reported feeling like they performed better.

What Can You Do to Help Athletes Perform Better in the Heat?

Many of the studies about precooling don't support the practice. However, without precooling, heat illness is still entirely preventable. Although it is interesting to learn about new methods for enhancing sports performance, sometimes the best methods are ones you already know and use in your fitness programming.

Specific Training

The Principle of Specificity pertains to sports movements as well as environments. You can train a cross-country skier in the gym, but to get them ready for their competition, you need to take them outside. There are also many other benefits to training in the great outdoors. Learn more: How to Take Your Workout Outside And Why You Should.

Acclimation

Although precooling methods don't seem very effective, they do seem to produce the same effect as with acclimation. When creating exercise programs, make sure to get athletes out in the elements so their bodies can adjust.

Heart rate is the best predictor of heat stress. Closely check athletes. Record heart rate periodically throughout practice. If an athlete shows any of the symptoms of heat stress, pull them out and let them cool off.

How Long Does It Take an Athlete to Acclimatize to Heat?

Acclimation can take 8 - 14 days and in some cases up to two months.

Some studies find that acclimation improves the athlete's tolerance to discomfort during heat but may not change the physiological processes which would improve performance. Other studies find the opposite. They suggest that acclimation helps with:

• Earlier onset of the sweat response

• Improved cardiovascular efficiency

• Reduced cardiovascular strain

• Slower increase in core body temperature

Bottom line: Acclimation is the best chance your athlete has at improving their performance in different conditions. Keep a close eye on your clients as they get used to the environment.

Proper Hydration and Nutrition

Dehydration is a key factor in developing heat illness. Ensure that your athletes hydrate before, during, and after practice and competition.

It is also important to coach your athletes, especially high school- and college-aged clients, the importance of good nutrition. Our article, Nutrition for Active Teens - What Trainers Need to Know, is a great resource.

Precooling as Necessary

You may find that one or more of these precooling methods is beneficial for your client. Use these methods as necessary to prevent over-heating, especially in extreme heat.

Education

Make sure that you can identify the signs and symptoms of heat-related illnesses. Make sure your clients can identify the signs and symptoms of heat-related illnesses.

Educate the parents and coaches of your young athletes on the importance of proper training, hydration, nutrition, and rest. Don't let the coach make all the calls if you know some policies or traditions (two-a-day practices) are unsafe.

Avoid Extreme Heat

If extreme heat is in the forecast, cancel the game or practice. It is ALWAYS better to be safe than sorry.

If you'd like to learn more about working with athletes, check out the ISSA Specialist in Strength and Conditioning course.

References

Cooper, E. R., Ferrara, M. S., Casa, D. J., Powell, J. W., Broglio, S. P., & Resch, J. E. (2016). Exertional heat illness in American football players: when is the risk greatest? Journal of Athletic Training, 51(8). doi:https://dx.doi.org/10.4085/1062-6050-51.8.08

Crandall, C. G., & Gonzalez-Alonso, J. (2010). Cardiovascular function in the heat-stressed human. Acta Physiologica.

Howe, A. S., & Boden, B. P. (2007). Heat-related illness in athletes. The American Journal of Sports Medicine, 35(8).

Jones, P. R., Barton, C., Morrissey, D., Maffulli, N., & Hemmings, S. (2012). Pre-cooling for endurance exercise performance in the heat: a systematic review. BMC Medicine, 10(1). doi:http.dx.doi.org.proxy.lirn.net/10.1186/1741-7015-10-166

Mohammed Rahimi, G. R., Albanaqi, A. L., Van der Touw, T., & Smart, N. A. (2019). Physiological Responses to Heat Acclimation: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Journal of Sports Science and Medicine, 18(2).