Summer is coming, temperatures are rising and going for a run or cycling becomes an act of bravery. In this situation, common sense tells us that we should avoid the middle hours of the day, hydrate ourselves more and slow down, even though there is a possibility of falling into the sedentary lifestyle. This is why it is vital to adapt our exercise and rest to the high temperatures we are facing.
The thermal shock. When we exercise, our muscles generate energy, but only 20-25% is translated into mechanical movement and the rest is released as heat. If we add to this a hot environment, the body faces a double thermoregulatory challenge.
As detailed in an exhaustive review published in 2021Under heat stress, the body diverts a large flow of blood to the skin to dissipate heat through sweat. This means there is less blood available to working muscles and the heart. The result? The heart rate skyrockets to try to compensate and exhaustion comes much sooner.
Acclimatization. The good news is that our body is an extraordinarily adaptable heat machine, and that is why if we expose ourselves to heat progressively, we activate what is known as acclimatization. Here, a study published in 2024 quantified this adaptation and it was seen that, after a period of repeated exposure to heat, the participants managed to reduce their core temperature at rest by 0.19 ºC and their heart rate by 6 beats per minute.
That is, follow a process of adaptation 8 to 14 days Heat training consistently improves performance and thermoregulation. In fact, from the fifth day onwards, cardiac adaptations begin to be noticed.
The physiology. Something that has been seen is that in the first week of heat training, the body retains more water and sodium in order to increase the blood volume that runs through the arteries and veins with the aim of improving cardiac output and the supply of oxygen to the muscles.
The good thing is that if we maintain the thermal stimulus long term, the body responds by creating more hemoglobin, which is the protein that transports oxygen through the blood. This makes the system much more efficient when training, since the muscle will have a greater amount of oxygen.
Train with heat. Just because the heat offers physiological advantages does not mean that we should go running at three in the afternoon during the heat wave in August, since there are serious complications such as heat stroke. Here the recommendation states that exposure to heat should be progressive, with short sessions at low intensity and increasing the duration over two weeks.
Logically, hydration must be maintained according to physical activity, since dehydration of more than 2% of body weight nullifies many of the advantages of acclimatization and dangerously increases internal temperature. In short, training in the heat is hard but little by little it is possible to adapt as long as common sense prevails, changing the training schedule also to times with lower temperatures.
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