By: Barbell Logic Team

Your body has an impressive ability to adapt to different climates, including excessive heat or cold. Increasing environmental temperature is a form of stress (heat stress) just like training is a form of stress, and you have adaptive behavioral and physiological responses to both acute and chronic exposure to the heat. Below we talk about these responses and ways to help you stay safe and beat the heat while you train this summer.

Training in the Heat

Depending on where you live right now, you may be dealing with extreme heat or oppressive humidity. If there is any downside to training in a home gym, it is dealing with the seasons’ extremes. In the winter it’s stiff muscles and cold barbells. In the summer, we have to train in or around the heat. You may be trying to decide whether to keep regular training hours, even if it means suffering in the heat, or to adjust your schedule for a cooler but less optimal training time. As you are dealing with the heat, here are some things you should be aware of and ways that you can stay safe and maintain your training performance.

Built-in Adaptive Responses

Your body has an impressive ability to adapt to different climates, including excessive heat or cold. Increasing environmental temperature is a form of stress (heat stress) just like training is a form of stress, and you have adaptive behavioral and physiological responses to both acute and chronic exposure to the heat. Behavior modifications are probably obvious: you wear less clothing, drink more water, and use technology like A/C to help keep you cool. You do these things because you are uncomfortable; being uncomfortable is a self-protective response that your body uses for thermoregulation. 

Physiological responses to small changes in heat are limited. You maintain your core temperature by vasodilation of your skin. When your superficial blood vessels widen, blood flow from your body’s core to the skin surface increases, and sweat evaporation transfers heat away from your body. Accordingly, many adaptations to chronic heat stress revolve around maintaining your fluid balance and improving your body’s ability to transfer heat from your core to your skin where it can be cooled.

This response is the same whether you are in dry heat or humidity, and both climates offer different challenges to staying cool. In dry climates, your sweat evaporation is rapid, having the potential to burn through your body’s water supply more quickly. This increases the risk of dehydration and, in extreme cases, may require an intentional approach to maintaining your fluid balance. Humidity, on the other hand, keeps sweat from evaporating. This hinders your ability to cool your core temperature and can cause you to risk overheating. In dry climates, adding moisture to the air or your skin directly can help with your evaporative cooling. In humidity, convection methods like a big cooling fan can make a difference by helping sweat evaporate from your skin. 

It’s important to recognize that as impressive as your adaptive responses are, they operate best in small changes. In a review of adaptive homeostasis, one author makes a point of distinguishing between your body’s adjustments to smaller, non-damaging stresses and adaptations to “toxic” or “harmful” stressors. He writes, “Multiple protective systems demonstrate great transient plasticity in response to very small changes in oxygen, oxidants, temperature, acid, alkali, salt, exercise, etc. In numerous well-documented examples, these are such small changes that they cause no damage at all.” He distinguishes this adaptive homeostasis from hormesis or recovery and adaptation to harmful changes. While hormesis is possible with certain stressors—the physiological equivalent of “that which does not kill us, makes us stronger”—it is not something you want to test out with heat stress.

The risk of too much heat or an excessive rise in core body temperature is the risk of hyperthermia. Hyperthermia is often cited as an increase in your core temperature above 45°C. But an individual’s susceptibility can vary depending on his or her current acclimation to heat stress. A better definition is that hyperthermia occurs from “a rise in body temperature above the hypothalamic set point when heat-dissipating mechanisms are impaired (by drugs or disease) or overwhelmed by external (environmental or induced) or internal (metabolic) heat.” (Bouchama A, Knochel JP, “Heat Stroke” N Engl J Med 346: 1978-1988 (2002); see also Beker BM, Cervellera C, De Vito A, Musso CG, “Human Physiology in Extreme Heat and Cold,” Int Arch Clin Physiol 1:001 (2018).) The range at which different people can experience hyperthermia can be as low as 37.5°C to 38.3°C (or 99.5°F to 100.9°F). Once your adaptive responses are overwhelmed, you risk exhaustion, injury, or illness. It’s important to understand your limits and to mitigate your susceptibility to heat stress.

Beat the Heat

There are three main ways that you can beat the heat and minimize your loss of performance in the summer swelter:

Being Trained: Unless you are new to lifting, you have already been preparing yourself to withstand climate changes without a drop in performance. According to sports scientist Dr. Périard, “Well-trained athletes have a larger plasma volume and may display better central venous pressure and cardiovascular stability under heat stress than their untrained counterparts.” Athletes exhibit a greater adaptive capability, in general. This suggests that being trained will make you more sensitive to changes in your environment, making your vasodilation and sweating mechanisms more responses to changes in external temperature. (Julien Périard, “Prolonged Exercise in the Heat,” Aspetar Sports Medicine J. (available at https://www.aspetar.com/journal/viewarticle.aspx?id=49#.XTH2F5NKjUI))

 

Acclimatization: Sudden changes in heat can more easily overwhelm your responses. Acclimate yourself and adjust your behavior to give your body a better chance to make adjustments to the heat. This means that a sudden heatwave can be more dangerous than the normal gradual heat of summertime. As you acclimate to the heat, your body improves its capacity for heat dissipation as compared to a sudden exposure. (See, id.)

 

Hydration: This is important for keeping cool and for maintaining your performance in training. Increased heat, combine with a shift in your fluid balance as you sweat, can increase cardiovascular strain and lead to a greater reliance on muscle glycogen as you exercise. (Id.) Early depletion in glycogen can directly affect your force production capabilities, especially on the last set of a high volume training day. For lifters, erring on the side of caution, drinking more water, has little potential downside. So, drink up.

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