cycling in hot weather

Beat the Heat Series: PERFORM at Your Best During Hot Weather Exercise

Introduction: Heat is the enemy of endurance performance and an underlying cause for diminished performance, dehydration, heat stress, gastrointestinal distress, and impaired recovery. In this 3-part series we will provide you with the tools and information you need to PREPARE for training and events, PERFORM at your best, and RECOVER optimally when temperatures soar.

Quick Facts:

  • Consume cold drinks when you can. Ice slurry drinks are not better than cold fluid during exercise.
  • Drinks are for hydration, food is for energy. Separating them allows you to adjust fluid and calorie intakes independently in response to heat and intensity.
  • Water vs. Sports Drink: water for short (60-75 minute) workouts. Water and sports drink for medium duration (1-4 hour) workouts.
  • Both water and sports drink should be used for very long (4-10+ hours) workouts/events, but be aware to avoid taste fatigue and gastric distress.
  • Warm up or start slow in order to let your sweat response ramp up with your effort level.
  • Wear lighter clothing (weight and color), unzip, douse yourself with water, and/or use ice socks/packs to assist with thermoregulation.
  • Slow down, get wet, and sip plain water if you become nauseas from overheating.

Part 2: PERFORM at Your Best During Hot Weather Exercise

In Part 1 of the Beat the Heat Series we talked about how to monitor your day-to-day hydration, increase your fluid intake through deliberate choices throughout the day, acclimate to high temperature environments, and pre-cool your body to delay the onset of heat stress. But no matter how well you prepared you are, you still have to get out there and PERFORM at your best in the heat.

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Hot Weather Hydration

Sweat rates increase dramatically when training or competing in hot weather, reaching levels up to 1.5 liters per hour. Replacing 100% of fluids lost is not typically achievable, but it is important to replenish enough fluid to limit your fluid weight loss to about 2% of your total bodyweight. In cooler weather athletes may be able to get away with greater fluid weight loss and still perform at a high level because they can redistribute their reduced blood volume to working muscles with less risk of overheating. In hot weather, the competing priorities of staying cool and delivering oxygen to working muscles mean you have a smaller margin for error.

Hot weather hydration seems like it should be simple: drink more. And generally that is true, but when you are interested in performance (rather than just survival), the following strategies will optimize your hot weather hydration status:

Hydration in your bottles, calories in your pockets

Separating your hydration from your energy intake allows you to increase your fluid intake in hot weather without overloading your gut with more calories or sugar than you can handle. When you consume a mixture of sugars your gut can absorb about 60-90 grams of carbohydrate per hour. Overloading the gut with more carbohydrate than you are adapted to can lead to nausea and gastric distress, even if it is less than 60 grams/hour. The likelihood of gastric distress increases even more in hot weather because reduced blood flow to the gut slows absorption and gut motility. Recommendations for electrolyte intake is about 500-700mg of sodium per hour, and this can come from food and/or sports drinks. Overloading with too much sodium can lead to nausea. When your primary source of calories is food you can adjust your calorie intake based on your intensity level and independently adjust your fluid intake based on your thirst, sweat rate, and thermoregulation goals.

How much should you drink?

Sweat rates vary widely from person to person and according to exercise intensity and environmental conditions. Your goal is to limit fluid-related weight loss during exercise to 2% of total bodyweight or less. Standard hydration recommendations for endurance athletes are 20-40 ounces of fluid per hour (1-2 bottles). This can increase in hot environments to 50-60 ounces (2.5-3 bottles), but many athletes struggle to consume this much – or more – on an hourly basis due to limits on gastric emptying; consuming too much fluid can lead to discomfort (sloshing stomach) or nausea. Your ability to consume large volumes of fluid is trainable, so with practice you can gradually increase your hourly fluid intake. Even so, limitations on fluid intake increase the importance of thermoregulation strategies, discussed later in this article, for assisting in heat dissipation.

What about hyponatremia, the dilution of body fluids that can become very dangerous or even fatal? There are different types of hyponatremia, and the two that affect endurance athletes most are hypovolemic and hypervolemic. Hypervolemic hyponatremia can result from consuming excessive amounts of water and failing to replenish electrolytes lost via sweating. Bodyweight increases, and swelling is often present. Hypovolemic hyponatremia is characterized by low serum sodium levels but no increase in total body water, and in some cases even reduced bodyweight. Ultraendurance athletes are susceptible to this form of hyponatremia because over a long period of exercise (10+ hours), they are gradually losing sodium and also sweating continuously. Hypervolemic hyponatremia is often caused by excessive consumption of water in relation to sweat loss. Hypovolemic hyponatremia is more a problem of excessive sodium loss resulting from prolonged sweating, adequate fluid intake, and inadequate sodium intake. Neither is common, and both are easy to avoid by consuming electrolyte rich foods and drinks during prolonged exercise.

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Water or Sports Drink?

Hydration should be the primary goal of the contents of your bottles, which always leads to the question of whether you should consume sports drinks or water. The answer is both. Here are some considerations to help you choose:

  • Short workouts (60-75 minutes): Water is likely sufficient because you won’t dramatically deplete electrolyte concentrations or need exogenous carbohydrate energy in that timeframe. Fluid intake takes priority.
  • One to two hours: Athletes typically don’t feel like eating much when it’s hot, so for 1-2 hour workouts, starting with a bottle of sports drink and a bottle of water gives you a source of some calories and electrolytes that you’re more likely to actually consume. For workouts longer than an hour, exogenous carbohydrate intake is beneficial, but you shouldn’t wait until you reach an hour to start eating.
  • Two to four hours: Now you’re at the point where you’re going to need to refill bottles or use a hydration pack to carry enough fluid to meet your needs. Packing single-serving packets of sports drink mix allows you to continue carrying one bottle each of plain water and sports drink. If you’re using a hydration pack, still carry one bottle on the bike that you can use for sports drink.
  • Four to 12 hours: As you get into longer workouts or ultradistance events, the importance of consuming electrolytes increases. They can come from your food and/or drinks, and it is best to combine these sources. However, both taste fatigue and gastric distress can become a problem for athletes in ultradistance events, so it is important to be prepared with plain water available.
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What the heck is in my sports drink?

At its essence a sports drink is water with stuff dissolved in it. Some drinks have lots of different kinds of stuff dissolved in them, most of which just waste space. There is only so much room to dissolve solutes in a drink, and drinks with fewer ingredients can use more of that room for important things such as carbohydrate and sodium. The simplest drinks are the best because they are easiest on the gut and facilitate the transport of sugar and electrolyte across the semipermeable membrane of the intestinal wall better and faster. Here’s what matters most in a sports drink:

  • Concentration: When you change the osmolality of the fluid (the total molecular concentration of everything in the drink—carbohydrate, electrolyte, flavoring, additives—per unit volume), it changes how the drink influences the overall mixture in your stomach, and hence how that mixture makes it into the intestine. Sports drinks are formulated to optimize the absorption of carbohydrate, fluid, and electrolyte. If the osmolality of the sports drink is too high because of a bunch of additives, it may contribute to slower gastric emptying. When the osmolality of sports drinks is lower, it is more likely to contribute to faster gastric emptying (depending on what else you’re eating and drinking), and if it’s being consumed on an empty stomach, it is formulated to get into the intestine quickly.
  • Short Ingredient List: If you are designing a sports drink to have a relatively low osmolality but you want it to deliver moderate to high amounts of sodium and/or carbohydrate, you have to eliminate other stuff to make room. That’s a big part of the reason we’ve seen drink manufacturers shift to drinks with shorter ingredient lists. The primary ingredients you’re looking for are one or more sugar sources, sodium (preferably as sodium citrate), potassium, and flavoring.
  • Light, slightly diluted taste: Putting electrolytes and flavoring into a fluid makes you want to drink more frequently and consume more fluid each time you drink. A lightly flavored drink is preferable to a stronger one because when you consume half a bottle in one long slug, the stronger-tasting drink becomes overwhelming and you stop drinking sooner. A drink that tastes almost watered down when you are at rest will taste just about right when you are exercising.
  • Tart flavor: A slightly tart drink will encourage you to drink more than an overly sweet one, and citrus flavors also increase the drive to drink. It should be no surprise, then, that almost every drink company has some version of lemon-lime in its product line. In addition to the flavor, a sports drink needs to clear the mouth well. When a drink leaves a film in your mouth, as is often the case with overly sweet drinks, it’s not only unpleasant, but you’re not likely to drink again soon.

The characteristics above are common to several high-quality sports drinks designed specifically for athletes. At CTS Camps and Events we supply our athletes with Real Hydration from Bonk Breaker.

Drink Temperature

This is a subject that has generated a ton of research. From a practical standpoint I believe it boils down to this: Cold water is good. Ice slurry drinks are good for pre-cooling but not better than cold water during exercise. Both options will become room temperature or hot water pretty quickly, so the effect/benefit can be important but relatively short lived. What does all this mean when you walk into a convenience store a few hours into a hot ride? Fill your bottles with ice cubes and water to put on the bike, and grab a sports drink or sugary drink to consume now. As you continue down the road you’ll have food in your pockets and for a while you’ll have cold water to drink.

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Thermoregulation Strategies for Exercising in Hot Weather

For purposes of this discussion, we’re going to assume you have already applied the heat acclimation and workout scheduling strategies outlined in Part 1 of the Beat the Heat Series. When you are training or competing in hot weather, think of thermoregulation strategies as a way to alleviate some of the burden placed on your primary cooling mechanism, sweating. If you can reduce sweat rate or you’re your body dissipate more heat than through sweating alone, your performance will improve and you will have a better chance of maintaining a good hydration status.

Some of the following tips will be obvious, but that doesn’t make them any less true or valuable:

  • Warm Up To Cool Off A good warm up is vital in the heat because it lets your evaporative cooling system get up to speed before you do. Jumping right into a hard effort spikes your body temperature before you’ve started sweating enough for your system to begin cooling you. One of the benefits of greater fitness and acclimation is that your body begins sweating earlier; it’s much easier to keep a body cool than to use sweat to cool it once it’s overheated. To stay on the safe side, start workouts off slowly when it’s hot.
  • Wear light-color and lighter-weight clothing: Apparel companies like Panache and others have developed lighter-weight summer tops that allow for increased airflow to the skin and improved moisture wicking. Darker colors absorb heat, whereas lighter ones reflect it.
  • Unzip or go sleeveless: Especially if you’re wearing standard tops, unzipping will increase airflow to the skin and keep the jersey from trapping heat close to your body. And although bike racers need covered shoulders, athletes can train with sleeveless tops and increase airflow to the underarms, an area that is very good for heat transfer to the environment.
  • Get wet: Evaporative cooling carries heat away from the body as fluid water turns to vapor. From a cooling perspective it doesn’t matter if that fluid came from your sweat glands, a hose, a creek, or a water bottle. But from a hydration perspective it can be crucial, because dousing yourself with water can help reduce sweat rate, preserve more blood volume, and give you a better chance of consuming enough fluid to stay in a good hydration status.
  • Ice packs: Fans of professional cycling may remember seeing team cars handing riders stockings or mesh bags filled with ice on hot days. These can be placed on the back of the neck, between the shoulder blades, in jersey pockets, or in the front of a jersey. The only complaint some athletes have with ice socks/packs is that more water tends to end up in your shoes than when you dump a bottle over your head or back.
  • Tailwinds make you hotter: This isn’t a tip so much as a heads up. Headwinds are more painful to ride into, but the increased airflow over your body helps keep you cooler. In a tailwind, the difference between your speed and the wind speed is smaller, so airflow over your body decreases. Tailwinds mean higher speeds, but sometimes greater heat stress, especially on long climbs.
Working through a heat crisis

Despite preparing for heat and trying to apply good hydration and thermoregulation strategies while exercising in the heat, there may come a time when you make a mistake, get lost, or run dry, and end up in a heat crisis. For endurance athletes, nausea is one of the most common first effects of a heat crisis. When you overheat, gut motility slows or stops as blood flow is directed to the skin and working muscles. This means food and fluids sit in your gut, slosh around, create gas, etc. If you get nauseas during a hot weather workout or event, take it as a sign you are overheated and take action with the following steps:

  • Slow Down: Muscles generate a ton of heat, so slowing down can help reduce the internal heat you are producing. This can give your overtaxed cooling system a chance to catch up. Try not to stop unless you have to. Moving forward gets you closer to home, an aid station, or a store. But if you do need to stop, seek shade and a breeze if possible.
  • Get Wet: Save some water for consumption, but try to find a way to douse yourself with water. Jump in a creek, stand in the lawn sprinklers, get creative.
  • Sip plain water: You want to get your gut moving again, but you have to be careful not to overload it. Don’t guzzle fluids, but do sip plain water. If it’s cold water, that’s even better.

What’s Coming in Part 3

Using the strategies in the PREPARE and PERFORM parts of the Beat the Heat Series, you should reach the end of your workout or event having performed well. You may still experience some level of diminished performance due to the heat, but the idea here is to minimize the decline so you are able to perform high quality work and/or able to compete at higher level than the competition. In Part 3, RECOVER, we will discuss post-workout and post-event hydration and thermoregulation strategies for maximizing recovery. This is especially important for athletes who are utilizing block training or participating in multiday events.

Chris Carmichael
CEO/Head Coach of CTS

Comments 4

  1. Pingback: Heat Illness and Endurance Athletes: The Science of Staying Safe When It Gets Hot - CTS

  2. Thanks for the great article. I had a chance to put some of these techniques into practice this past weekend…before the article came out! I despise riding in the heat and would prefer a winter ride any day. But we just rode in the Saints to Sinners relay, which goes from Salt Lake City to Las Vegas – in the end of July. Of course it would be hot, so I used your advice in the first article to start acclimating to the heat by riding in the middle of the day instead of the cooler mornings in SLC. I went for one of those rides with my wife and she couldn’t take it any longer and we had to turn around. I felt fine.

    The race is 522 miles and we did it in two 3 man teams. My legs were 73, 50, and 30 miles. The last leg was the toughest in terms of the heat. It was 111 F at one point in Las Vegas. We were fortunate enough to have a SAG vehicle that could meet us at any point to resupply us. My teammate and I used the following very successful strategy, which coincidentally, coincides with your recommendations. 2-3 bottles/hr of electrolytes. 3 bottles/hr of water over our entire body including our heads. Ice pack (in a leaky plastic bag) over the shoulders, 2-3/hr (whenever it melted). 2-3 electrolyte tablets every hour. We used S caps to get about 700-1,000mg NaCl per hour.

    I’ve never felt better. We finished the race feeling great. In retrospect, I could have even gone harder, but thought I should be conservative due to the heat.

  3. I start my rides with only an electrolyte solution in both my bottles. I then switch to a complex carbohydrate and electrolyte solution. For longer rides, I might use a combination solution including proteins and fats. Note: that’s the four and over rides. I do carry clear water with both. Also, if the only thing at the corner store is a commercial mix, drink it anyway. Use lots of clear water to dilute.

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