How can I deal with exercise in the heat?

Right now it’s the height of the warmest time of the year for us living in the Northern Hemisphere, and a lot of us are having to find ways of training and competing successfully in temperatures that range far higher than what we get most of the rest of the year. For those of us that live in coastal regions, like myself in the San Francisco Bay Area, most of the year, we may only see temperatures in the 50s and 60s fahrenheit (or the 10s c). This time of year, it may be up to 100 or more (over 35 c) when I ride over the hills for most of my rides. I’m sure it’s much the same for most of us. So what are we supposed to do about it? How do we cope with the heat? (I’ll try to keep it brief, but I’ll also just throw down some bullet points at the end to try to leave you with some basic take home points… so if you’re short on time, just skip to the bottom.)

Well, first off, I would want to point a few things out that should make us a little pleased that we get to work out in the heat. For one thing, when you engage in endurance training in the heat, your body makes adaptations that help you perform better across all temperature conditions, both cool and hot. That’s an area of research in which some people are showing interest, because it’s quite notable how much performance can increase after exercising in the heat. The most obvious change that occurs is that your blood volume increases as you retain more water, and you have an increased pool from which to draw for sweating and heat dissipation.

Another thing worth pointing out that is very important is that while you want to stay relatively hydrated when working out in the heat, you don’t want to overconsume water. If you get dehydrated, then you may slow down and see your performance suffer, but that isn’t cause for you to drink tons of water. Rather, drinking too much water can and will dilute your body’s electrolyte balance and can lead to hyponatremia, which is a more common cause of heat-related health issues, mainly related to poor nerve function and resulting heart problems. Also, somewhat ironically, getting slightly to moderately dehydrated in training is actually going to be more effective at helping you adapt to the heat than consuming tons of fluids and electrolytes, because doing so mitigates the actual fluid/electrolyte stresses of heat training.

Be aware that it is relatively rare for you to actually overheat in the heat. Most of what goes on with your reduced performance or a lowering of your tolerance of a certain pace or workload is a preemptive reduction of effort and increase in perceived exertion managed by your brain to keep you from overheating in the first place. Under all circumstances, keeping your body from overheating is a priority for your brain, but in the heat, you’re consciously and unconsciously aware that such an event may happen sooner, so you slow down more quickly or reach a state of failure sooner precisely because you’re avoiding a point where your body is in real danger. That’s not to say, that you can’t or won’t ever actually overheat and run the risk of real harm, but in general, for most people in most circumstances, you’ll quit or slow down before that happens. The biggest risk is probably when you have a driven, motivated athlete with a high pain tolerance and limited prior heat adaptation; then we may have more cause for concern.

Whether you’re exercising in the heat or in cooler conditions, you are almost necessarily going to lose weight during a training session of any substantial length. When your body stores glycogen in your muscles, it also stores 3-4 times the same mass of water, so if you burn through 500g of stored glycogen, you’re going to be taking 2000g of weight out of your muscles. (500g of stored glycogen is about the maximum usually quoted for a fully carbohydrate loaded endurance athlete.) So, even if you were able to fully maintain the same water and electrolyte balance over the course of running a marathon or doing a tough 5 hour bike ride, you’ll almost inevitably lose about 2kg (5lbs) of body weight. So, don’t panic if you come home from your ride and see the scales showing a loss of 1kg or more (2-3lbs or more). Rather, if you come home and you aren’t lighter, that probably means that you were consuming more fluids than is necessary or ideal, and you’ve diluted your body’s electrolytes, so you probably need to take in a little extra salt. You definitely should not be drinking enough fluids to avoid any and all weight loss during a training session. If you do, you’re increasing your risk of hyponatremia. You should drink as much as you are thirsty, and make sure that you’re taking in electrolytes along with your fluids, but expect to lose a little water and carbohydrate weight during any training session lasting more than about an hour or two, running or biking respectively.

In any case, the biggest thing that can be done to increase your performance in the heat is to just get used to it by training in the heat. When you train in the heat, you will not be able to maintain the same power output or pace for as long as you would be able in cooler conditions, so you should just be aware of that and accept the fact that you will be slightly slower and usually feel more fatigued in the later portions of your workout sessions. Still, because the changes in water retention are probably the most significant adaptation you get to the heat, the most helpful training you can do in the heat is endurance training (i.e. longer and less intense rather than shorter and more intense). Doing longer sessions in the heat will lead you to lose more fluids and will cause a greater stress on your body’s heat management and water retention mechanisms, and for that reason should yield the most gains in performance once your body adapts. Again, this is most helpful when you train long enough to get at least a little dehydrated. You should always be drinking and taking in electrolytes, but over the course of a longer training session, some level of dehydration is probably inevitable.

For shorter training sessions, there is much less time to lose fluids and and therefore have more limited ability to sweat and cope with the heat, so you can often do fairly intense short rides even in the heat, but longer ones can’t be done with the same intensity as they can when it’s cool. One nice thing about the heat is that your warm-up time will be reduced for the obvious reason that it’s warmer outside and it will take less time for your blood vessels to dilate and your working muscles to get up to their optimal operating temperature. So, don’t be concerned about being unable to get in the intensity you want on the days that you plan harder workouts, because you can usually get it in early or late in the day, or by just condensing the time taken for the workout so that you don’t get too hot or dehydrated.

Aside from the actual internal changes that your body makes to cope with the heat from training, there are things that you can do with your body to help it cope better. When you train in the heat, your body produces anti-diuretic hormone (or “vassopressin,” depending on where you’re from), and your body doesn’t give up as much water. Another way to force your body to retain water is to increase your sodium consumption. So, it’s important for endurance athletes to consume more sodium in the heat, to help them absorb and retain more water and to replace the salt that is inevitably lost through sweating… One of the worst things you can do is to be on a low-sodium diet in the heat and to simply increase your water consumption, because it reduces your body’s ability to retain water and increases your risk of hyponatremia, both of which are performance limiting and potentially risky to your health. So, that being said, after working out in the heat, be sure to drink an electrolyte drink mix, eat salty snacks, or even consider a product like Pedialyte to keep your body’s electorlytes topped off.

Lastly, a lot can be done while you’re exercising to keep cool. First off, make sure that you have appropriate apparel. Namely, wear lighter weight, more breathable fabrics and less layers. Consider pouring water on your head and body. The cooling effect of cold water on your head, neck and upper back and chest is profoundly relieving and can reduce your perceived exertion and prolong the time you can sustain a hard effort. Even if you don’t have cool water on hand, even warm water has a profound cooling effect, because as soon as it’s on your skin and it starts to evaporate, heat will be drawn from your body as the evaporating water molecules take thermal energy with them… this is the reason that sweating works. As sweat or other fluids evaporate off your skin, they take heat with them and cool you off. And, along similar lines, consider putting ice in your jersey. Ice-socks are usually made of short stretches of panty-hose material filled with ice and then tied-off. These can easily be handed up to competing athletes and tucked under their jersey behind the neck and will help the athlete stay cooler longer.

So, what’s the take home, and what do I do? Something like the following:

– try to train in the heat, so that you can adapt to it

– pre-hydrate and stay hydrated with fluids and electrolytes when you need to perform well

– don’t be afraid to get a little dehydrated when you’re training, because it’s inevitable with longer sessions and it will help you adapt (still be sure to drink and take electrolytes, just don’t overdo it)

– never just drink a ton of water, you won’t retain it well and you’ll dilute your body’s electrolytes, which can be risky

– stuff ice in your clothes, pour water on your head, and stay cool while reducing your body’s need to sweat

– take in extra sodium before competition, so that you’ll retain more water and perform better

– take in extra sodium after competition and training so that you replace lost electrolytes, retain water better, and keep your body in healthy balance

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