#101 Exercising in hot conditions

Since training and mountain outings normally take place outdoors, we are inevitably at the mercy of Mother Nature when it comes to the weather. Heading out in all weather helps you build valuable experience, but you still need to expose yourself to it gradually. Today, we tackle the summer question: how do you prepare and exercise when it's hot?

Our body, a heat generator

Our body is a thermal machine, producing either mechanical work or heat. So when we exercise, our body temperature rises. This warming is the result of our muscles' poor efficiency, which converts only 30 to 40% of energy into mechanical movement. The rest, more than 60%, is released as heat, dissipated through the skin and the air we exhale. During sustained effort, most of this heat is managed through conduction and thermal convection. Without going into the details, there are two points to remember:

Our body will first try to cool itself with air, then start sweating to transfer more heat if necessary. Since the temperature difference is smaller in summer, sweating kicks in almost automatically as soon as we start moving. Now, if cooling is not sufficient, the heat warms up our system and raises our body temperature dangerously. The brain then shuts down functions one by one, at best reducing our athletic performance, at worst exposing us to heatstroke. Fortunately for us, there are methods to help the body dissipate heat more effectively.

Acclimatizing to heat

Acclimatizing to heat: the effects

Heat acclimatization is a method available to athletes who plan ahead. If you know that at some point you will have no choice but to head out and exercise in the heat, you can prepare for it in the weeks beforehand. Recent studies conducted with the help of professional cyclists have shown that training in high temperatures has the same physiological impacts as altitude. Indeed, after long training sessions in hot conditions, the body adapts to cope in the same way as if it were exposed to a deficit in atmospheric pressure. The fastest change is the increase in plasma volume in the blood. This increase allows better thermal regulation, reduces the metabolism's energy consumption and increases the thermal tolerance of cells. The second change is the increase in the number of platelets, which determines the blood's hemoglobin level. More hemoglobin means it is easier to supply cells with oxygen, which translates into increased performance. In the end, the benefits of heat acclimatization are:

Acclimatizing to heat: the protocol

Hot sessions should be integrated little by little, building up to one hour per day, five to six days per week, over several weeks. These sessions should mirror aerobic development sessions, that is, walking or running at an intensity strictly below Z2. Studies have also proven the beneficial effects of 20 to 30 minutes of sauna, a hot jacuzzi or, at worst, reading in an attic at the height of summer. Nevertheless, keep in mind that the return on "hot" sessions is low. For one hour of training per day, five days per week, over five weeks, the maximum performance gain did not exceed 10%. These sessions should be considered as a complement to your initial training plan, which itself should be carried out in cooler conditions. Be careful to prepare your body properly for this extra effort: the increase in blood volume demands very good hydration and a sufficient iron level to facilitate platelet creation. There could be differences between men and women in this adaptation, as the studies were conducted mostly on men. And since you will be drinking more often to stay hydrated, also make sure you avoid hyponatremia by consuming electrolytes, especially sodium.

Planning your outings

During heatwaves, you can adapt your training to the weather. In particular, you can move intense sessions to early morning to train in milder temperatures. It is also possible to move them to late evening, but we do not recommend it. On the one hand, air pollution is higher. On the other hand, the session will be too close to your bedtime, degrading the quality of your night, and therefore the quality of your recovery. Planning your outings also means defining the content of the session. Let's not forget that the heat generated by the body is a consequence of muscular work. The less work there is, the less we will need to cool down. If you have no choice but to train in the blazing heat, favor base endurance sessions, in heart rate zone Z1. Finally, planning means anticipating the hot outing. Lowering your body temperature before heading out increases heat tolerance, as the body sets off "recharged with coolness". Several techniques exist for this. You can place wet towels on your chest and neck, drink cool drinks, or stay in the shade or in an air-conditioned place in the hour before the session. Finally, it is very important to set off well hydrated: make sure you have sufficiently topped up on water and sodium before heading out.

Cooling off

Now, long outings and competitions can force us to exercise at the worst hours of the day, without any choice in the pace to follow. The strategy then consists of artificially cooling the skin temperature and ensuring sufficient water reserves for sweating.

Hydrating

Hydration is key to protecting yourself from the heat. On a hot outing, you will need to plan enough water to reduce your fluid losses. However, the more sustained the pace, the lower the hourly volume will be. While it is easy for a hiker to drink 1 liter of water per hour, a runner will only drink a little more than 0.5 liter to avoid reflux. It is entirely possible to train yourself to drink to increase your tolerance, but that is something to plan for over the long term. Dehydration that makes you lose 2 to 3% of your weight during effort is not serious. However, don't tempt fate by pushing further: being lighter, and therefore moving more easily, will be offset by a loss of both your physical and mental capacities. However, over-hydrating is also a problem. Less well known, overhydration (hyponatremia) is also dangerous. If you drink too much water, the sodium (salt) level in your blood will drop, slowing your digestive system's ability to process water, and therefore your ability to hydrate. Sodium allows cells to regulate the amount of water they can hold. When there is too little sodium, cells swell up, to the point of creating, in extreme cases, pulmonary and cerebral edema (as with mountain sickness). So favor sodium-rich drinks during your sessions.

Cooling off artificially

To cool off, you can splash yourself with cool water (better yet, immerse yourself) or drink cool drinks. For short outings, this study compared the two techniques and the possible combinations. It is interesting to see that the chosen method (drinking, splashing, both, nothing) had no impact on the athletes' performance (over a 5-kilometer running outing). Yet drinking and dousing yourself did reduce body temperature, but this only affected how the runners felt. One obvious point: drinking nothing and not splashing yourself with water is the worst of the combinations. Splashing yourself is the most effective strategy in terms of sensations, although drinking a cool drink had the same effect on body temperature. For long outings, the mind is very important. Even if cooling has no impact on short-term performance, maintaining a level of comfort helps you last over time. Our physical capacities are heavily influenced by our mental state. We can therefore imagine that keeping your head in an ok place for longer must show in performance. In cases where water is limited, it is better to drink than to splash yourself, in order to maintain a good level of hydration. You can also target the areas to cool. The head, hands and feet are the areas to prioritize: cooling the skin in these spots provides better cooling of the blood.

The risks of exercising when it's hot

The risks a healthy athlete is exposed to in hot weather are:

The warning signs include, among others, fatigue, a loss of lucidity, nausea, and elevated breathing and heart rates. In these cases, you will need to act quickly to restore a good thermal balance. Quickly seek to cool the body artificially, either by finding a shaded area or by splashing yourself with water. Without forgetting to hydrate with an electrolyte-rich solution. In any case, the best defense against heat remains prevention: avoid exercising during the hottest hours and remember to hydrate properly.