Winning in the Heat – Tips for Racing in High Temperatures

In the spring and summer, internally generated heat limits training intensity and affects the outcomes of races. Only about one fifth of the energy released by a athlete’s body during cycling ends up as useful work, with the other four-fifths emerging as heat. The higher the power output, the higher the heat production. Cruising along at 200 Watts (a reasonable all-day pace for a fit, medium sized cat-3 or 4 male) the body is generating ~800 Watts of heat, as much as eight 100-Watt light bulbs. On a cold day, that heat production is nice. One can ride comfortably in clothing in which one would freeze standing around. Cool air blowing over skin, even through a few layers of clothing, carries heat away as fast as it is generated. If one warms up a little, a bit of sweating keeps body temperature from rising more. Body temperature stays in the optimal range.

As ambient temperatures rise, riders dress more lightly so they can continue to dissipate waste heat as fast as it is produced. Muscles function optimally at an internal temperature of 101-102F (38-39C). At high enough air temperatures, it’s not possible to remove enough clothing to maintain optimal body temperature while pedaling hard. As internal temperature rises higher than the optimal range, performance decreases. The air temperature above which a rider’s performance will be impaired depends on conditioning, humidity, clothing and other factors that vary from individual to individual. For all riders, the ability to dissipate heat, rather than aerobic capacity, will become the primary limiter to performance in warm enough conditions.

When a rider pedals, the brain sends signals telling the muscles to push, but there are many inputs and feedback loops between the part of the brain that sends the initial request for pedal pushing and the signal that gets to the legs. In particular, as core temperatures rise beyond 102F (39C), the lower brain partially blocks signals from the upper brain to the legs. Thus at higher temperatures, one has to make a greater mental effort to maintain the same power. This is a survival mechanism. If one continues to generate heat faster than it can be dissipated such that the core temperature gets up around 106F (41C), the brain dies. Toughness allows one to work a little harder for a little longer, but success in hot races depends on controlling core body temperature far more than on being able to tough it out.

Dealing with Heat

High temperatures impair performance for all riders, but adoption of certain strategies can decrease the impairment, giving one an advantage over riders who do not employ those strategies or do not employ them as consistently or effectively.

1) Acclimatize to heat.

Regular, prolonged exposure to heat causes increases in blood-plasma volume and more uniform sweating over more of the body. Sweating removes heat only when the sweat evaporates from the skin. More uniform sweating leads to less dripping and more evaporation, allowing more heat to be dumped per amount of fluid sweated out. Increased plasma volume means a rider can sweat away more water before becoming dehydrated enough to impair performance. These two effects together allow an acclimated rider to perform better in heat than an unacclimated one.

One can identify acclimation visually. People who are not heat adjusted drip from their hairlines, armpits and crotches and become lethargic in heat. Acclimated people glisten all over, and stay energetic.

Efficient sweating and increased plasma volume delay dehydration and maintain blood supply for the muscles longer. Acclimatization allows one to continue to generate power where another rider would be slowed more by the heat. Heat acclimatization requires being warm enough to be sweating a little most of the time. Riding in heat and then returning to an air-conditioned building will not cause much acclimatization. Many hours spent a bit warm, riding or not, triggers the desirable changes more than riding in extreme heat. Get in the habit of wearing long sleeves, long pants and a hat when anywhere cooler than the race venues of the next few weeks. You’ve probably seen pictures of pros wearing caps and jackets while people around them are in shorts and tee shirts. They are not afraid of drafts. They are maintaining their heat-adjustment. Adjustment takes a few weeks to get going, and a few months to optimize, so start adjusting well before the hot season.

You don’t need to be exposed to extreme heat to adjust to heat. Training in sauna-like conditions will help prepare you mentally for the suffering of racing on hot days, so some actual training in heat is beneficial. More is not better though. When one trains in extreme heat, power production might be down 20-50% or even more for the same perceived effort. The effect of training on fitness development depends on the actual power produced, not the feeling of effort.

Heavy sweating makes it challenging to maintain hydration and electrolyte balance, so training in extreme heat requires more recovery time than a similar volume of training done in more hospitable weather. If it will be hot at mid-day, most of training should be done in the morning or evening or even in air-conditioned indoor spaces if that is the only way you can keep cool.

2) Train by heart rate rather than power, or develop hot-day power zones.

The stress on the body of generating a particular wattage on hot days is greater than the stress of generating the same wattage on pleasant days. Trying to hit normal power zones for the normal amounts of time on a very hot day “fries” riders. For riders who like to track such things, heat effectively increases the intensity factor of a given power output. Either base power zones for hot days on a hot-day FTP, or train by heart rate, being sure to back off when it is harder than usual to maintain your usual heart rates.

3) Keep Skin Wet.

Water evaporating from the skin cools the body. Water in the gut doesn’t. Drinking enough to maintain hydration is essential to performance, but beyond keeping up with sweat losses, drinking more doesn’t keep one cooler. Sprinkling water on the jersey and shorts and through the helmet is much more effective. Carry an extra bottle for this purpose (and remember which one it is so you won’t put sports drink on your hair). Arrange to take multiple bottles at feeds. If you are dropping out of a hot race, give your bottles to teammates first.
Cold water is better than warm for both drinking and putting on the skin on hot days, but just barely. The amount of heat it takes to warm up cold water is miniscule compared to the amount it takes to evaporate it, so use cooler water when available, but don’t sweat about it. Ice absorbs a huge amount of heat as it melts, so ice vests and other ways of keeping ice against the skin can dramatically improve performance when heat is a limiter.

4) Dilute Sports Drink if needed.

Many riders feel bloated if they drink full-strength sports-drink on hot days. Mix sports drink at partial strength or alternate sips of sports drink with plain water. You don’t need and can’t absorb as much sugar as you will get with all the water you need on a really hot day. If you don’t feel bloated on hot days drinking full-strength sports drink, you may need to take more fluid.

5) Shorten the warm up.

A good warm up for a well trained rider takes most of an hour if not longer on a cool day, but a full-hour warm up on hot days will lead to overheating unless one can find a cool place to do it, such as in an air-conditioned store or school. If a cool space is not available, one should get organized and dressed and then sit in an air-conditioned car until about 25 minutes before the race, giving the legs a bit of rub-down while waiting. Getting out 25 minutes before start time and rolling around for 20 minutes, with just a few jumps at the end will prepare the body for harder work without risking overheating. Go to the line with wetted clothes and hair a few minutes before your start. If part of the start area is shaded, being there gives a further advantage.

6) Choose Summer Kit.

This should be obvious, but wear light colors if your team was smart enough to design light-colored kit. No matter how much the marketing materials talk about wicking action and efficient cooling, bare skin cools better than any fabric, though it doesn’t block sun. If it is not sunny, the lightest and thinnest clothing that covers the least possible skin is best. The body will absorb heat from the sun though, so on extremely sunny days, thin, light colored fabric over more of the body can be better. A bit of air space under the fabric is better for cooling, but worse for aerodynamics.

7) Carry a Belly Bottle.

Drink as much as you comfortably can in the final minutes before the start of a hot race or training ride. That way one can effectively carry three bottles, one in the belly and two on the bike.

8) Dial in Fluid Needs.

Weight yourself before and after rides. If you lost approximately one pound, you drank the right amount. If you lost more, drink more on your next ride of similar length in similar weather, one pint for each pound lost. If you are gaining more than a pound or two during rides, you are at risk of hyponatremia, a potentially deadly dilution of your blood electrolytes. Do not drink enough to gain weight on rides. Figure out and keep track of how much you need to drink on various rides. Plan for one additional small bottle per hour in a race compared to a training ride of the same length.

9) Sometimes, Hydration Backpacks are for smart people.

In temperate areas, it’s common for MTB riders to use hydration packs while road riders look down on them. In very hot areas, road riders know that hydration packs are the only way to carry enough water for a longer ride. Riders in temperate areas should take a clue from their desert dwelling siblings when their hometowns start to feel like the desert.

10) Supplement electrolytes.

Electrolyte needs vary a lot from rider to rider, but the hotter it gets the more people need to specifically supplement electrolytes. If you have no trouble in the heat, don’t worry about this, but if you suffer a lot, get yourself some electrolyte supplements and use them according to the directions. Each small bike-bottle of water that you sweat away carries about a half-teaspoon (2.5 grams) of salt. Multiply that by the number of bottles you drank on a ride to know how much salt needs to be replaced over the course of the day.

11) Look for salt.

Riders don’t show salt on their helmet straps, shorts or jersey backs until they begin to dehydrate. Once one is dehydrated enough to start sweating extra salt, it takes several days to get electrolyte balance back. Drinking water and eating salt help, but consuming them doesn’t immediately put them in the right compartments within the body. That takes time, so it’s much better to stay hydrated than to try to correct hydration and electrolytes post-ride. If you have salt on your kit, drink more on the next ride. If your competitor has salt on his or her kit, attack!

12) Keep a good attitude.

If you can convince yourself that you are good at riding in the heat you’ll have a double advantage over riders who get bummed out about the discomfort. First, being positive is an advantage in itself. Second, being positive helps you keep doing the things you need to do to take care of yourself, further growing your advantage.

13) Adjust tactics.

Increasing intensity means increasing heat production. On a day hot enough that heat dissipation is the limiter for most of the riders, attacks become self-limiting. A moment after attacking, a too-hot rider loses strength and comes back to the field. Chasers are also lazier. Take these facts into account when deciding whether to attack, or to help with a chase on a hot day.

14) Don’t be Stupid.

No matter how well acclimated you are and how well you follow these suggestions, at very high temperatures, especially if it is humid as well, it becomes impossible to keep body temperature in a survivable range while riding hard. If you start to feel light headed, or your skin turns intensely red, or you start to shiver or turn white on a hot day, you are approaching very serious, potentially deadly, trouble. If you have any of those signs, immediately get into a cooler place or at least some shade, and dowse yourself with the coldest available water or ice to get core temperature down as quickly as possible. Continuing to work hard with these signs of heat illness can literally kill one quite quickly. Watch teammates for these signs and help them make the right choices to stay alive. There will be other races. Be smart.

Doing It Right

Riding in extreme heat impairs performance for everyone. Most people find it at least mildly unpleasant. If you follow the suggestions above though, extreme heat will impair your performance less than the next rider’s, so heat actually becomes an advantage for you. Good luck with the hot season races.