Beat the Heat
Well the summer has been a hot one once again! It’s a good time to think about heat stress on the body and how to deal with it when you are getting ready for a race. Like other stresses to the body such as training stress, sunburn, or physical damage, the body must recover from heat in order to be able to perform at its best. Think about staying cool and get a jump on the competition!
Basics: The human body is highly thermo-regulated and strives to maintain the temperature within a narrow margin of 37 degrees C. Temperatures above or below this optimal body temperature cause the body to react to maintain the temperature within the desired range. Failure to do so can result in decrease in biochemical and biomechanical functioning, including the breakdown of proteins and membranes, and eventually death. Heat is gained by the body from solar radiation and radiation from the surrounding environment. In the summer, the problem is increased because the difference in temperature between the body and the ambient air and environment is decreased, thus heat cannot be removed from the body as rapidly as in cooler temperatures. Additionally, heat is generated in the body as a by-product of the inefficient production of mechanical energy (pedaling force and muscular contraction). In fact, only about 30% of the potential energy generated from the burning of fuel in the body ever gets to generate work on the bike.
Problems: Heat stress has been recognized as a very serious matter for the athlete. Not only can excess heat cause major physical problems including heat exhaustion and even heat stroke, the body will act to decrease athletic performance far before catastrophic failure of the body. Higher body temperatures can alter the voluntary ability of an athlete to continue with an event in the attempt of the body to stop the stress. The ability of the body to recruit muscles to work decreases with heat stress (Morrison et al, 2004), and the rate of decline of voluntary power output decreases in hotter environments.
Losing the heat: When the body generates this excess heat, the body responds to dissipate the heat. The body can lose heat in a number of ways. The first few are of little effect on losing heat from the body: 1) the body can lose heat from respiratory exchange (the hot air coming out of your mouth) and 2) conduction, which is the loss of heat as it is transferred from one solid to another, such as through the handlebars or saddle. Obviously, those are of little effect on cooling a body that is burning 1000C per hour. The body also loses heat through convection, which is heat loss when air travels over the body and through evaporation of sweat or water from the skin. Water has a high specific heat, which is the amount of energy required to increase its temperature. Thus when water is evaporated away from the body, it takes a lot of thermal energy with it, and it is the most effective way for the body to lose heat. For an athlete, the only thing that you can really change is the amount of heat lost from the evaporation of water from the skin, and it is the most effective method, so we will focus on how to maximize the ability of the body to do so in order to keep the athlete cool.
Using cooling strategies: As an athlete, keeping cool can allow the body to continue to generate high levels of physical performance, and possibly give you an edge over other athletes that are suffering from heat stress. In general this can be done in a couple of ways.
Most importantly, before (like 1-2 days) and during the event keep hydrated!!! You cannot lose heat from the body without proper plasma volume to sweat with! Sweating is the most important way for the body to dissipate excess heat. Performance can decrease with the loss of just a few pounds of water from the body, so make sure that you are drinking enough. Use sports drinks to help with fluid retention, and use color charts for urine to try to monitor hydration. In all cases be safe out there, wear sunscreen, drink and eat wisely, and don’t push yourself over the limit! I found that being hydrated the night before the event and then just drinking wisely the day before can maintain your hydration without causing you to have to urinate excessively before and during the event. Listen to your body!
Second, one can acclimate to exercising in higher heat. In a lab study, researchers found that an increased core temperature of 1-2 degrees c for 60-90 mins over 4-10 days was sufficient to induce an acclimation response (Pandolf et al, 1977) , but aerobically fit individuals decreased the required stimulus (Cheung et al, 2000). To put it in simple terms, you can acclimate to heat by doing 60-90 mins of workout in the heat for a number of days, and it will be easier for you to do so if you are already fit. If you are going to do a heat acclimation regime, be sure to drink plenty of water, and heed your body’s exhaustion signs. If you are sweating heavily, you are probably getting a good stimulus because increased sweating rate is a big component of the acclimation process. Heat acclimation is thought to be achieved through increased plasma volume (the amount of water in your blood) and rate of sweating. In general, if you are doing some exercise in the conditions in which you are going to race you are probably already doing some acclimation, so attempting to design an acclimation program is probably unnecessary and pushing yourself to the limit of heat tolerance is a bad idea. Be safe.
Finally, other body cooling strategies before an event may be important too. It has become popular for professional teams to wear cooling vests and ice packs in the jersey before and even during events in high heat. The idea is that if you can decrease the baseline temperature before an event, you have more time at high metabolic output before you reach temperatures at which your body decreases performance. Cooling the core body and head are important, but warmed up legs are still an important part of race preparation. I have found that putting ice into panty hose, then putting them into the jersey pockets or upper back during warmup and the first part of a race can help with perceived and actually body heat and be very effective. The panty hose allows the water to drain out and cool the body by conduction and evaporation while not requiring the athlete to carry around the melted water, which simply drains out. Additionally, when warming up for your event, stay out of the sun and heat.
For additional information on this topic, as well as other advanced topics on cycling performance, I suggest the book “Cutting Edge Cycling” by Allen and Cheung.
Cheung et al. (2000) The thermophysiology of uncompensable heat stress. Physiological manipulations and individual characteristics. Sports Medicine 29:329-359.
Morrison et al. (2004) Passive hyperthermia reduces voluntary activation and isometric force production. European Journal of Applied Physiology 91:729-736.
Pandolf et al (1977) Role of physical fitness in heat acclimatization, decay, and reinduction. Ergonomics 20: 399-408.
Scot Ferguson is a USAC level 2 coach and certified in Power Based
Training (CPBT). Scot is a long time collegiate cyclist and raced for many
years with the UNR cycling team. He now coaches the UNR cycling team as well
as his own personal clients and strives to help them succeed. Additional
information about his coaching programs and contact with Scot can be found at