Essential Nutrition Strategies for Training or Racing in Hot Weather

Are you struggling to adapt to the sudden rise in temperatures during your training sessions? Understanding heat acclimatization can make all the difference. You’ve been training all winter in colder weather, then all of a sudden your race next week is thirty degrees warmer!  What can you do to better acclimate training in warmer weather?  It all starts with planning ahead before your race and understanding more about acclimation.

What is Heat Acclimatization?

Adaptations to training in the heat depend on the intensity, duration, and frequency of exposure. It usually takes about 7 to 14 days of heat exposure to induce heat acclimatization. Optimal heat acclimatization requires a minimum of daily heat exposure of about 90 minutes combined with aerobic training.

What happens to My Body During Acclimatization?

During the initial exposure to heat, core temperatures and heart rate are elevated, increasing sweat rate and perceived effort. Training at race pace will feel much harder than in cooler temperatures. However, with daily exposure to heat, improvements in heart rate, skin and core temperatures, and sweat rate are achieved within the first week. These benefits can last for about a week but reduce by about 75% by the third week once heat exposure ends. This variability is why spring training can be tough, with temperatures fluctuating frequently.

Three classic signs of heat acclimatization are a lower heart rate, lower core temperature, and higher sweat rate during exercise-heat stress. Sweating may start earlier at a lower core temperature after acclimation, improving cardiac output and making training efforts seem easier.

How Can I Acclimate to the Heat When Training in Cooler Temperatures?

If you are still training in cooler weather but have a reace In warmer temperatures, you can expose yourself to heat through home-based options include daily exposure to a hot room, hot bath, or sauna.  You can even try to simulate training in the heat by running on the treadmill by switching on the heater and humidifier on.

However, be aware of the risks of heat training, including dehydration, higher fatigue levels, and potential heat exhaustion. Always consult your physician before performing heat training.

How Can I Prevent GI Issues When Training in the Heat?

Gastrointestinal (GI) issues during training and racing limits the intensity at which you can perform well. Long durations of exercise in the heat are known to contribute to GI distress due to the potential reasons:  

• Reduced Blood Flow to the GI Tract due to cooling the body, blood is diverted to the skin and muscles, reducing gut blood flow by up to 80%, impairing the gut lining.

• Increased GI Permeability ("Leaky Gut") due to the heat the gut barrier is compromised, leading to the entry of harmful substances into the bloodstream, triggering an inflammatory response. 

• Delayed Gastric Emptying due to reduced gut function slows digestion, causing bloating, nausea, and fullness, especially during endurance events.

To mitigate GI issues during longer training sessions or racing in the heat, hydrate well prior to and during sessions longer than 60 minutes and train your gut to be able consume enough fluids and carbohydrates to prevent poor sports performance.

How Can I Adjust My Hydration When Training or Racing in the Heat?

First of all you need to know your sweat rate.  Training in cooler temperatures decreases sweat rates but once wamer temperatures increase you need more fluids to prevent dehydration.  Test your sweat rate before and after heat acclimatization to determine the amount of fluids and sodium you may need when racing in warmer temperatures. 

Popular take home tests to determine your sweat rate include the Gatorade Sweat Patch or Nix Hydration Biosensor. Precision Nutrition or Levelen offer individualized sweat rate tests including the amount of sodium you need during endurance events. However, using sweat rate patches or sensors have their strengths and limitations but can provide a good estimate of how much fluid and sodium you need.

You can also perform a sweat rate test by weigh yourself before and after a 60 minute training session to figure the amount of fluids you need.  However, just weighing yourself only identifies the amount of fluid you need and not your sodium losses.

Start Well-Hydrated. The latest hydration recommendations include to drink about 4 hours before your event by slowly drinking 5-7 ml (0.17-0.23 ounces) of fluid per 1 kg of body weight (2.2 pounds). For example, if you weigh 150 pounds, 68.1 kg, you would need about 25-34 ounces of fluid over 4 hours before your event to be well-hydrated.  If you only have about 2 hours before your event, it’s suggested to reduce your fluid intake to about 16 ounces (about 2 cups) to avoid any gut issues or excessive urination during the event.

Add Sodium. Consider adding 300-500 mg sodium per hour to your fluids with a small amount of carbohydrate to improve fluid absorption, especially when sweat rates are high. You may need more than 500 mg of sodium per hour, but you won’t know exactly how much sodium you need unless you perform a true sweat test calculating sodium losses.  Using sports nutrition products such as Skratch Sport Hydration or Tailwind are great options to provide not only sodium but a small amount of carbohydrate to aid with fueling as well.

Consider Pre-Hydrating. Pre-hydrating with a high sodium beverage (500-1000 mg sodium) 2 hours before exercise has been shown in small studies to prevent dehydration when exercising in the heat.  But does this mean we need to pre-hydrate the day before with electrolytes? Probably not.

The days leading up to a big endurance event, as long as you are not sweating excessively, all you need to do is drink to thirst and monitor your urine color making sure it’s a pale yellow indicating you are well- hydrated. There is no benefit from drinking excessively before your event than you normally would, placing you at higher risk of diluting your blood sodium levels (hyponatremia) and additional sodium lost in your urine, potentially leaving feeling fatigued and negatively impacting your health. 

How Should I Adjust My Fueling Plan When Training or Racing in the Heat?

Eat Enough Carbohydrates. In addition to hydration, eating enough carbohyrates during longer training sessions are necessary to maintain energy levels and prevent depleting muscle glycogen stores. Carbohydrates can improve the palatability of fluid and drive the desire to drink more during exercise. They can aid in fluid retention since carbohydrates are bound to a certain amount of water when stored as glycogen.

Consuming carbohydrates during exercise maintains blood flow to the gut which can mitigate GI distress. When training in hotter temperatures, carbohydrates are used at a higher rate, which may indicate it would be advantageous to consume carbohydrates in the form of a sports drink (which would also include beneficial electrolytes).

Recommendations for endurance athletes range from 30-90grams of carbohydrate per hour, and can even be advantageous when training with short sprint bursts due to the ability of carbohydrates to excite the brain and decrease feelings of fatigue. 

Choose Multiple Carbohydrate Sources. Glucose and fructose (or sucrose) combinations use different intestinal transporters allowing higher total carb absorption (up to 90 g/hr vs 60 g/hr for glucose-only). Using carb gels, chews, or beverages containing combinations of carb sources helps reduce GI distress and improves performance in long-duration events.

Take Home Message  

• Monitor urine color: Pale yellow = hydrated. Dark = dehydrated. Start training or racing well-hydrated to prevent GI issues and dehydration.

• Consider pre-hydrating before endurance training or racing in the heat.

• Have a hydration plan when training or racing in the heat, based on your personalized sweat rate.

• Watch for signs of heat stress: nausea, dizziness, headache, GI cramping. These can be worsened by dehydration or overconcentration of fluids/carbs.

• Choose multi-transporter carbs to improve absorption and maintain energy during hard workouts or endurance events.

• Acclimatize gradually: The body needs 7–14 days to adapt to heat training. During that period, hydration and carb intake are even more critical.

References:

1. Racinais S, Hosokawa Y, Akama T, et al. IOC consensus statement on recommendations and regulations for sport events in the heat. Br J Sports Med. 2023;57(1):8-25. doi:10.1136/bjsports-2022-105942 

2. McCubbin AJ, Allanson BA, Odgers JNC, et al. Sports Dietitians Australia Position Statement: Nutrition for Exercise in Hot Environments. International Journal of Sport Nutrition and Exercise Metabolism. 2020;30(1):83-98. doi:10.1123/ijsnem.2019-030

3. Superior Endurance Performance with Ingestion of Multiple Transportable Carbohydrates. Accessed December 4, 2022. https://oce.ovid.com/article/00005768-200802000-00012?relatedarticle=y

4. Lorenzo S, Halliwill JR, Sawka MN, Minson CT. Heat acclimation improves exercise performance. J Appl Physiol (1985). 2010;109(4):1140-1147. doi:10.1152/japplphysiol.00495.2010

5.     Morris DM, Huot JR, Jetton AM, Collier SR, et al. Acute Sodium Ingestion Before Exercise Increases Voluntary Water Consumption Resulting In Preexercise Hyperhydration and Improvement in Exercise Performance in the Heat. Int J Sport Nutr Exerc Metab. 2015 Oct;25(5):456-62. doi: 10.1123/ijsnem.2014-0212. Epub 2015 Mar 26.