The struggle of having to exercise in hot weather is all too real. While many people simply forgo their daily fitness regimen when the heat is too much to bear, for an athlete in training, skipping a workout could mean throwing their body and training schedule completely out of whack. If you fit in this category you probably have a meticulously designed training plan that has been tailored to your needs—one that’s meant to be followed and that doesn’t allow for days off due to hot weather.
"Depending on where you find yourself, summertime may mean warm breezes and captivating thunderstorms...or it could mean dangerous, sweltering heat. What the summer sun doesn't have to be is a break in outdoor fitness or a reason to put your training on hold."
Living in a region that regularly experiences high temperatures doesn’t mean your training is at risk—it means that you have to be more mindful of how and when you train. As a cyclist, you spend a significant amount of time exercising outside; there are certain considerations and adjustments that need to be made to your training plan and schedule. Knowing how to prepare for the kind of heat you’ll be riding in, being aware of the symptoms of heat-related illnesses, and making mindful decisions can be the difference between enjoying your ride or winding up in the hospital.
Kinds of heat
Not all heat is created equally. When people describe kinds of outdoor heat, they often describe them in relation to humidity levels. Humidity levels are expressed as a percentage, with zero percent indicating that there is absolutely no moisture in the air and 100 percent indicating that the air is completely saturated and can not hold any more water. Humidity levels vary with location and elevation; Florida has a tropical humid climate while Nevada is a desert with very low humidity. The amount of moisture in the air really does affect your body’s heat tolerance, which is easy to overestimate, especially without proper conditioning.
High humidity
Everything changes when you train in humidity. The higher the humidity levels, the more noticeable and more dangerous high temperatures become. Heat affects your body’s ability to function, often rendering it unable to respond to its environment. Higher moisture levels makes it harder for sweat to evaporate, diminishing your body’s ability to cool itself down and putting you at risk of overheating.
Because it takes an extra toll on your body, exercising in humid weather feels harder. The best thing you can do to ensure safe training is to acclimate. Once you start acclimating, you’ll find that your body responds differently in extreme temperatures, which is why doing it right is so important. When you begin, you’ll notice that your sweat rate will go up, your average pace will drop, hard efforts will feel almost unsustainable and recovery will be hard. Even your water intake habits change as humidity changes. Be sure to drink plenty of fluids, but only drink enough to satiate your thirst—don’t force yourself to guzzle more water than feels comfortable.
Low humidity
The US southwestern states—Colorado, Utah, New Mexico, and Arizona—have a climate low in humidity and therefore described as a “dry” heat. Training in environments low in humidity isn’t necessarily easy, but it will certainly feel a lot easier than training in higher humidity levels. One thing to always keep in mind when riding in drier climates is that it’s not hard to become dehydrated or suffer from another heat-related ailment—especially if you’re not used to such low moisture levels.
Relative humidity
Relative humidity is generally expressed as a percentage and is the amount of water vapor in the air compared to the maximum amount of water vapor that could be held at that temperature. Lower relative humidity means sweat evaporates so quickly that oftentimes you don’t realize that you’re sweating! When you don’t realize you’re sweating, you’re less likely to replace lost fluids and more likely to become dehydrated. To stay hydrated throughout your ride, set a periodic reminder on your bike computer or watch for every 10 or 15 minutes, and take a sip every time it goes off.
Heat index
Humidity affects how heat feels and is explained with the heat index scale. Heat index refers to what the temperature feels like to the body when relative humidity and air temperature are combined, and is generally how we decide what clothing is most appropriate for the day. Air temperature feels warmer if humidity levels are high and cooler when humidity levels are low. Once humidity levels rise to or above 40 percent, there’s a noticeable slow-down of sweat evaporation and consequently heat dissipation, which ultimately makes your workout feel even more difficult.
Dangers and heat
When it comes to training in the heat, you really can't be too careful. The heat is dangerous because it can jeopardize how your body normally functions, throwing it out of whack and putting you at risk of illness or death. You can overheat in different ways, so familiarizing yourself with some body basics can help you understand the best ways to protect yourself and perform better in the heat.
Sweating
Your body’s primary way of cooling itself is through the process of perspiration, or sweating. The harder you ride, the more you will sweat. When your body realizes it’s starting to overheat, it tells itself to start sweating. When sweat evaporates from your body, it helps regulate and lower the overall temperature. In dry conditions, it’s easy for sweat to evaporate, but in humid conditions, the evaporation process is a bit more challenging due to the moisture contents already in the air. Instead of evaporating as it normally does in dry conditions, sweat begins to pool up on the surface of your skin, trapping heat and putting you at risk of developing a heat-related illness.
Because sweating is the primary cooling mechanism, as you adapt to the heat, your body improves how it sweats:
- Your sweat rate increases—oftentimes more in high humidity
- Your blood plasma volume increases, which assists with cooling by promoting blood supply to skin and muscles
- You start sweating at a lower core temperature
While sweating is your body’s main method of cooling itself, it isn’t the only way your body works to maintain a normal temperature. Working muscles are responsible for most of the heat that’s being produced within your body, so in addition to cooling off its surface through perspiration, the body also requires some sort of internal cooling mechanism to keep core organs at safe temperatures. Blood is the coolant circulating through the body’s machinery, carrying heat away from hard working internal organs to the radiators, skin and lungs, for dissipation. Blood plasma, which constitutes 55% of blood fluid, is 92% water by volume, which is why it’s critical to stay hydrated. When you perspire more than the amount of fluids you take in, you’re lowering the efficiency of this cooling mechanism.
Energy production
In order to perform at an optimal level, you must also understand the basics of the human body’s energy production. Unfortunately, the human body isn’t particularly energy efficient, so only around a third of the energy obtained from your nutrition is translated into forward motion, with the majority of your caloric intake going toward producing heat. The heat produced by your body has to be dispersed. Both energy production and dissipation play are critical to homeostasis and disruption of either of these processes quickly puts you in danger of a heat-related illness.
Radiation
When exercising outside in the summer sun, you’re exposing yourself to ultraviolet (UV) radiation, which is also a source of heat. You want to prevent your body from absorbing external energy as much as possible, since it’d be forced to work extra hard to dissipate it. In addition to direct sunlight, reflective surfaces, such as pavement, water, and glass are secondary sources of radiation that are often overlooked.
Respiration
Respiration plays a big role in how your body handles a variety of environments—especially heat. Whenever you exhale, you must dissipate heat. There are situations where you might gain heat from breathing instead, when the ambient temperature is higher than your body temperature
Conduction
Conduction occurs when heat is lost as a result of two solid masses or bodies coming into contact with one another. Commonly overlooked, conduction is another way your body gains heat, but it’s generally transferred to you by your bike. It’s not unheard of for someone to end up with a second degree burns on their butt, courtesy of black gel-filled bike seats.
Common heat-related illnesses
The human body loses fluids through everyday bodily functions such as breathing, sweating, and going to the bathroom. Through drinking fluids and eating food, those lost fluids are generally made up, ultimately keeping the body balanced and in check. If water isn’t replenished, the body will struggle to function properly.
Always be consciously aware of how you’re feeling. It’s easy to get caught up in the moment and to forget to drink. Knowing the warning signs to pay attention to means you might be able to take necessary action early enough to avoid suffering any serious heat-related illnesses.
Heat stress
Heat stress develops because the body can no longer rid itself of excess heat. When this happens, your body’s core temperature continues to rise. The most frequently experienced symptoms of heat stress are:
- Heavy perspiration
- Clammy skin that may be cold or pale in color
- An increased heart rate that may feel weak and rapid
- Fatigue
- Dizziness
- Headaches
Even though heat stress doesn’t sound especially dangerous, it can be. That’s why thinking that you should “muscle through it” isn’t going to cut it at this stage; the only safe course of action is to stop exercising and seek appropriate treatment as soon as possible. When you ignore the telltale warning signs, the risk of developing more serious heat-related conditions goes up dramatically.
Dehydration
Dehydration occurs when your body loses more water than it receives, a result of not drinking enough when you’re perspiring. The severity of dehydration depends on how water deficient you are and is described as mild, moderate, or severe. The beginning signs of dehydration include:
- Thirst
- Dry or sticky mouth
- Headache
- Muscle cramps
- Nausea
- Dry, cool skin
- Infrequent urination
- Dark yellow urine
Dehydration can become severe and cause additional symptoms, such as:
- Dizziness
- Fainting
- Sleepiness or lethargy
- Confusion or irritability
- Sunken eyes
- Rapid breathing
- Rapid heartbeat
If you notice the first warning signs of dehydration, don’t dismiss them. Instead, stop riding your bike, move to a cooler area, and replenish fluids and electrolytes. Medical attention may be required, depending on the severity of dehydration.
Heat stroke
Heat stroke is what happens when your body can no longer control its temperature, which could result in temperature reaching as high as 106 degrees in just a matter of 10 or 15 minutes. Not only is heat stroke a fast-acting condition, but it can also leave its victims with lifelong disabilities or even result in death. Heat stroke symptoms that could develop include:
- An elevated body temperature, often higher than 103 F
- Confusion or altered mental status, such as not knowing where you are or slurred speech
- Hot, dry skin or profuse sweating
- Nausea
- Dizziness, passing out, or losing consciousness
- Headache
- Seizures
If there’s a chance you may be experiencing heat stroke, lower the body temperature by moving to a cooler place and call for help immediately. Even though you might think it’s a good idea to guzzle down liquids to rehydrate, don’t; any liquids consumed should only be sipped until medical assistance arrives. If iced or cold water and some kind of cloth is available, wet the clothes and place them on areas of concern; the head, neck, armpits, and groin should be prioritized, but if possible, also cover exposed skin to help cool down.
Heat exhaustion
Heat exhaustion is what happens when the body has lost a significant amount of either water or salt, or in some cases both. Excessive sweating is the most common culprit of heat exhaustion, with symptoms including the following:
- Headache
- Nausea
- Dizziness
- Weakness
- Irritability
- Thirst
- Heavy sweating
- Elevated body temperature
- Decreased urine output
If you notice signs of heat exhaustion, immediately move indoors or to a cooler, shaded spot and begin sipping cold water. Applying cold compresses (or in the absence of compresses, splashing cold water directly on) to the head, face and neck and removing unnecessary garments, including shoes and socks, can help cool down core temperature. Go to a clinic or emergency room immediately.
Heat cramps
Excessive sweating exhausts the body’s salt and water levels and causes an imbalance in the body. When salt and water levels reach a certain low point, muscles are prone to develop cramps. If you’re training for an endurance event, there’s a good chance you’ve already experienced one. Symptoms of heat cramps include:
- Muscle cramps, pains, or spasms in the abdomen, arms, or legs
- Damp skin
- Heavy sweating
- Thirst
- Fatigue
Heat cramps are your body’s way of communicating with you and should not be ignored. For many people, cramps are also an indication of heat exhaustion. Stop pedalling, put your bike down, and tend to yourself by cooling your body down and replenishing lost fluids. This is one of those times you want to avoid salt tablets; stick to drinking plain water instead. If you have a snack, eat it. If there are carb electrolyte replacement liquids available, try those, too. Seek medical attention If cramps do not subside.
Training in the heat
Summer weather certainly brings a whole slew of heat-related challenges to overcome, but that doesn’t mean you have to compromise your ride; it just means you’ll have to be smart about how you approach it. The best way to avoid cutting your ride short due to illness is to take conscious steps to prevent it.
Avoid riding during the hottest part of the day
While you might not be able to control the weather, you certainly have some control over when you head out for a ride. Engaging in exceptionally strenuous training, including interval training and long rides, during the hottest hours of the day is really just a recipe for disaster. It’s best to avoid training during the hottest period of the day, which tends to be between noon and 5 PM. Instead, try to schedule any outdoor riding during early morning hours, when temperatures and UV radiation levels are their lowest.
If you’re going to train during those hours anyway, then at least be reasonable with yourself. Save longer rides for cooler periods and shorter ones for hot weather. Also understand that you’re going to have to maintain a slower pace and put out less power than you would on a cooler day. On hot days, it’s safer to ride by perceived exertion instead of heart rate, speed, or power. This isn’t the kind of temperature where you should be trying to set any PR’s because just attempting to could land you in the hospital.
Replenish lost fluids and other vital nutrients
Perhaps the most obvious way to avoid succumbing to the summer’s sun is by staying hydrated. A cyclist generally loses anywhere between one and two quarts of fluids through sweating during every hour ridden. In order to prevent dehydration, a minimum of whatever amount of fluids you perspire must be replaced; anything less results in dehydration. While aiming for one or two quarts an hour isn’t a bad idea, because everyone has different needs and hydration is such a critical element of training, it’s better to determine your personal needs and to plan ahead so that you ensure you meet them.
To stockpile your body’s fluid reserves before an upcoming event, increase your liquids intake a couple of days in advance. Don’t think you’re limited to just drinking water; consider upping your intake of super hydrating fruits and veggies, such as watermelons, grapes, cucumbers, and lettuce. Drinking electrolyte replenishing beverages will help you build up electrolytes and help with water absorption. Be sure to know your electrolyte limits so you don’t overdo it.
After a training session or race, consider a protein-based recovery drink instead of a carb-based one; protein carries water to the muscle, which will help rehydrate you even quicker. If water is your only option, then it’s best to take it with a snack or small meal packed with necessary nutrients, specifically protein, carbs, and sodium. If staying hydrated is difficult because you find yourself with warm water, then consider freezing one bottle at half full and another at around three quarters full of water, filling the rest of each bottle with cold water right before heading out. Hydration packs can be filled with water and thrown into the freezer, too! Not only is cold water easier to get down during a hot ride, but it also helps your body cool down.
Cooling down is essential
The safest way to train in the heat is by giving your body opportunities to cool down. As enticing as it is to dump a cup of ice down your jersey, professionals advise against doing so. Because ice causes blood vessels in your skin to constrict, it sends hot blood back to your core, actually working against the main objective. There are lots of great alternatives that not only feel better, but are more effective in getting the job done.
One easy way to cool down quickly is to either pour cool water over your entire body, especially the neck and forearms. Arm cooling sleeves soaked in cool water is also a great option to bring down your temperature.
Taking a break to cool down in an air conditioned building such as a cafe or a gas station during a particularly strenuous workout might feel like cheating but it also might be the key to success. If you’re planning a long ride in the heat, plan a pit stop to go to the bathroom, replenish your fluids and cool down. Ten minutes in an air conditioned building is enough to let your body recover just enough to hit your workout numbers with new gusto.
Wear moisture-wicking apparel
The body naturally cools itself through the sweating process, but that process can be thwarted if the heat produced by sweating gets trapped by clothes. If that heat isn’t released, then the sweat won’t be able to evaporate and cool you down, which could be all it takes to trigger heat illness. Avoid cotton-based fabrics, they absorb sweat rather than wick it. Instead, suit up in Lycra-based moisture-wicking apparel, which is designed to help keep you cool. A well-vented helmet is also a must for anyone who plans to ride in warm weather.
Fully protect yourself from the sun
Protecting yourself from the sun begins with protecting your skin. When presented with all options, always go for apparel that offers UV protection. There are countless options for cycling kits, arm and leg sleeves and under helmet caps made from fabrics that offer protection from the sun!
Out of all the organs, your eyes have the least resistance to UV rays, so help them out by wearing glasses that offer UV 400 protection. According to the American Academy of Ophthalmology, to be truly effective sunglasses must block 99% to 100% of UVA and UVB rays, and UV 400-protected glasses accomplish this goal. Finally, remember to slather some sunscreen on your ears, the back of your neck, and any other small areas that may be overlooked and unprotected.
Acclimatization is key
The human body in motion generally performs better in cooler temperatures, making your awareness of the kind of weather you’ll find yourself in especially important. It’s not even about making physical activity feel easier - it’s about helping your body function during physical performance because failure to acclimatize increases perceived effort and your risk of injury or illness. To help your body tolerate heat that it’s unaccustomed to, it is imperative that you work through an acclimatization program. If you’re accustomed to training in hot and humid weather that is comparable to anticipated race day weather conditions, then you’ll have less prepping to do than someone who lives in a dry, arid environment.
The idea behind acclimatization is to slowly build training intensity over the course of one or several weeks, depending on the program you’ve adopted. Research shows that when healthy adults are placed into conditions that elevate their core temperature by 1C to 2C for periods of 60 to 90 minutes over a period of 4 to 10 days, their bodies will elicit a lower core temperature, increased blood plasma volume and an increase in sweat rate. Because everyone is different, you’ll have to pay attention to how your body is performing and determine what intensity is tolerable and that doesn’t put unhealthy stress on your body.
There are lots of ways to slowly ease yourself into training in challenging environments. Saunas, steam rooms, and hot yoga classes are a few ways to get in some shorter, easier heat acclimation sessions. Even opting for no AC on a hot day could help your body slowly adjust. If riding outside is your absolute only option for preparing yourself for a change in climate, then be sure to take plenty of breaks and stay hydrated.
If you’re traveling to a race in a particularly hot location, consider showing up at least a week early and spending that time acclimating. Going “all out” on race day isn’t going to be worth it if you didn’t acclimatize—especially if it lands you in the hospital. Riding during times and temperatures that are similar to what is expected on race day is a good way to really gauge where you’re at, but use caution because it’s not hard to accidentally overdo it. If you happen to notice any symptoms of the heat-related illnesses mentioned above, take immediate action to prevent the development of anything serious; no race is worth injury or death.
“Once the sum of the temperature in Fahrenheit plus the relative humidity gets above 130, we dial power ranges back by about 10 to 15 watts,” he says. “If you’ve been doing 15-minute intervals at 220 to 240 watts, that becomes 205 to 225, or we may reduce the efforts to 10 or 12 minutes.” If you’re racing in steamy conditions, cut your warm-up time in half or more. And if you don’t track your watts, just dial back your RPE (rate of perceived exertion) a few notches—instead of riding at a 9, fall back to a level 6 effort.
The best way to know exactly what you need is by knowing exactly how much you sweat an hour, which can be determined by calculating your sweat rate. It’s actually very easy to figure out your sweat rate and just requires that you collect basic data about yourself, such as your weight before and after your ride and the amount of fluids consumed during your ride, and apply some basic math skills. It’s worth the small amount of time it takes.