I live in Texas, so I can confirm that even though it's only June, it is already very hot outside. I usually spend this time of year considering a relocation and wondering what is wrong with the people who write ad copy along the lines of "It's shorts season!" and "Outdoor training is back!" For one thing, I train outdoors all year round, and I know people who live in cold places that do the same. For another thing, I have been wearing shorts since February. We're way past "shorts season" at this point. This is "try not to die season".
If you've got a fall goal race on deck, you're probably looking at a summer full of grinding. The good news is that heat training provides a fitness stimulus, promoting adaptations that make you faster and stronger over time. The bad news is, training in the heat is the worst. Let's talk about how to make it (slightly) more bearable and safer, so you can get through your training block and crush that fall race.
Dial in Your Hydration
I'm sure it will not surprise anyone to note that in hot weather, hydration is really important. Why? Well, for one thing, a body weight loss of >2% during activity can result in performance decreases. And when it's hot outside, you sweat more, which means you lose fluids faster. You don't have to replace every ounce of fluid lost while you're exercising, but you want to take in enough to reduce that weight loss to <2%.
You can estimate your fluid losses by doing a simple sweat test - weigh yourself in dry clothes before and after a one hour run (don't drink anything during the run). Every pound lost represents about 24 oz of fluid per hour of activity in similar conditions. For example, if a 135 lb woman loses 2 lbs during her activity, she needs about 48 oz of fluid to fully rehydrate.
If you're doing a workout or race, or are otherwise concerned about your performance in hot weather, consider hydrating with an electrolyte replacement solution rather than water alone. The most effective rehydration solutions contain a concentration of electrolytes and carbohydrate (sugar) that is slightly lower than the concentration in your bloodstream. Salt and sugar act like helpers for the water, assisting it in quickly passing through your intestinal lining. Too much salt or too much sugar, however, can trap the water in your gut and cause stomach issues.
Salty and Watery Foods
Hydration during exercise isn't the only time to pay attention to your salt and fluid intake. Fortunately you don't have to just chug water all day. Eating foods that are high in water and electrolytes (things like sodium, magnesium, and potassium) can help keep you hydrated and prepare you for your next outdoor workout.
You're probably aware that lots of foods are high in sodium - generally, this is seen as a negative thing, because a lot of people need to reduce their sodium intake to manage chronic health issues (kidney disease, hypertension, heart or liver disease, etc). When it comes to endurance athletes, though, I usually like them to be a little more liberal with sodium, especially in the summer or for those that are particularly salty sweaters. That might mean including more broth, miso, salty snacks, or adding a little bit of salt to your food.
Potassium is found in fruits and vegetables, particularly in things like oranges, tomatoes, spinach, beets, watermelon, avocado, potatoes, and bananas. Magnesium is found in nuts and seeds, beans, dairy, and whole grains. Try incorporating these foods, along with foods with a high water content - such as milk (or plant-based milk substitutes), cucumber, melons, strawberries, and soups - to promote good hydration in the heat.
Carbs on the Run
It's not really groundbreaking news that runners need carbs, but it's even more important to keep your carb intake up in the heat. With increased exertion comes an increased reliance on carbs as a fuel source during activity. On runs longer than an hour, consider bringing along a simple carb in the form of gels, chews, sugar-containing sports drinks, or whole foods like dried fruit or a granola bar. Take your fuel with water to help avoid stomach problems. The body has a harder time digesting carbs during activity in the heat, so if you're not used to fueling during runs, start slowly and gradually increase your intake up to the recommended 30-60 gm carbs/hr of activity.
The heat also makes it extra important to fuel up before workouts and recover efficiently with a high carb, moderate protein meal or snack after a run. Something like a bagel, frozen waffles, banana or even juice can work well before heading out the door, while refueling with a fruit and yogurt smoothie, turkey sandwich, or chocolate milk (or soy milk) can help jumpstart the recovery process after your run.
Nitrates
Nitric Oxide (NO) is a compound that some evidence shows can improve oxygen transport and uptake in the body, improving exercise performance and tolerance. It's a vasodilator, which means it improves blood flow. You can probably see how these benefits would be especially helpful in tough conditions like summer heat and humidity!
NO is made naturally in the body, but consuming dietary nitrate can increase its production. Nitrates are abundant in leafy green vegetables (think spinach, chard, arugula), beets, and pomegranate. Some companies have developed sport-specific products like beet powder or chews that can also provide a benefit, but you don't have to buy a supplement to get the performance benefits. Including these foods regularly in your diet is sufficient. In addition, eating NO-rich foods within a few hours of exercise, may help improve your performance during your workout. Try mixing steamed or roasted beets or spinach into your smoothies or salads. Roasting beets with squash and potatoes is a great veggie-and-starch side for your dinner. Or try pomegranate arils on your yogurt bowl with breakfast.
Nothing can make running in the heat 100% comfortable, but by focusing on some easy nutrition adjustments, you can make it bearable. Training in the heat will help translate into faster times this fall, so it's worth it to stick it out. Make the best of it, and you'll be glad you did!
References:
https://www.gssiweb.org/en/sports-science-exchange/Article/sse-152-hydration-and-aerobic-performance-impact-of-environment
Burke LM. Nutritional needs for exercise in the heat. Comp Biochem Physiol A Mol Integr Physiol. 2001 Apr;128(4):735-48. doi: 10.1016/s1095-6433(01)00279-3. PMID: 11282317.
Gao, C., Gupta, S., Adli, T. et al. The effects of dietary nitrate supplementation on endurance exercise performance and cardiorespiratory measures in healthy adults: a systematic review and meta-analysis. J Int Soc Sports Nutr18, 55 (2021). https://doi.org/10.1186/s12970-021-00450-4
Jones AM. Dietary nitrate supplementation and exercise performance. Sports Med. 2014;44 Suppl 1(Suppl 1):S35-S45. doi:10.1007/s40279-014-0149-y