Should you exercise when it’s hot outside?

It’s a beautiful summer’s day.

All you want to do is be outside, enjoying the sunshine. As an active person, what better way to ramp up the enjoyment than to do something physical; like going for a run. So, you put on your workout gear, lace up your shoes, prep your tunes and off you go… mind ready and heart soaring.

The first steps feel good. Then something happens… your legs start to feel like they have a ton of lead inside them, weighing you down each time you plant your foot. You feel heavy.

This isn’t as fun as you had imagined! What’s going on?

It’s the heat.

Exercising in a hot environment

No matter how fit you are, or how often you’ve done a particular form or exercise, taking part in any physical activity in a hot environment dramatically changes the playing field.

Exercise is already stressful on the body, and heat takes this stress to a much higher level. If you’re not used to it, it can really make you feel like you’re out of your comfort zone, wondering where your fitness has gone. Additionally, if you don’t take precautions to deal with the heat, it can lead to serious risk of illness¹.

Why?

Well, one of the most immediate reactions is due to the physiological effects heat has on your body temperature. Additional heat and even humidity causes your body temperature to rise. In order to cool yourself off - your body needs to regulate your body temperature in a fairly narrow range - your blood pressure increases as a means to increase circulation through your skin to promote sweating².

As the cooling pathways become a priority, less blood is available to flow to your muscles. Not only does this cause that typical heavy feeling, it actually causes a further increase in heat. If you’re not compensating quickly enough through loss of sweat to cool you down, your body temperature continues to increase, which can be extremely dangerous and result in a condition called heat stroke³.

Heat cramps, exhaustion and stroke

Before you reach heat stroke, however, your muscles start indicating that something isn’t quite right. You may experience more pain in your muscles or cramping more than usual. If you don’t pay attention, the heat cramps can progress to a condition called heat exhaustion.  

Heat exhaustion makes you feel awful! You’ll be dizzy, feel weak, you may develop a headache, nausea and your skin will feel cold and clammy. If you still don’t move to a cooler environment and take care to replace the fluids you are losing through sweat, heat stroke is the next step.

Heat stroke is a very dangerous condition. By the time your body moves into a state of heat stroke, all of the resources it has to try to manage the situation and regulate your body temperature have been exhausted.

At this stage, your skin will be dry or barely moist from the lack of ability to produce the cooling sweat. Your heart rate may become erratic, you’ll suffer from mental confusion and you may even lose consciousness. It is essential to seek immediate medical attention should this occur as the consequences can be fatal⁴.

Now, this doesn’t mean you shouldn’t enjoy an afternoon run in the summer’s sun! The body has an amazing capacity to adapt, and it can learn to do so fairly quickly in response to temperature changes if you take the necessary steps to help it to do so^5,6.

Heat acclimatization

There are a few strategies that you can put in place to ensure you adapt to heat and reduce the stress effect that it has on your body^7,8.

First, it’s important to have some degree of fitness that has been developed in a cooler environment. The fitter you are, the better your body is at adjusting to temperature changes as it is better equipped to turn on sweating mechanisms as a means to remain cool. With this advantage, you can acclimate quicker in a hotter environment.

Hydration is another essential part of heat acclimatization. Providing enough fluid for your body to distribute to your working muscles and release in the form of sweat allows for better management of all of the mechanisms taking place when you are physically active in hotter climates. Often, water is sufficient, however, during extended periods of exercise, you may want to consider your electrolyte balance. Muscles use minerals to perform their actions, and your sweat is made up of salts. A hydration drink during or after a particularly long or tough workout in the heat may require replacement of these minerals.

Research shows that heat acclimatization can take as much as 14 days⁹. So, if you really want to enjoy the summer months, exercising outside, start making the necessary transitions as soon as you can. Helping your body to cope better with the stress of heat can be done from inside, too. Taking a hot shower after exercise, for example, promotes heat adaptations, as does making use of sauna therapy.

Whatever it is you do, make sure you do it safely. Take it a day at a time, listen to your body’s needs for rest or moving into cooler environment, and hydrate! In no time that lead in your legs will have vanished and you’ll be sailing through your run, sporting event or any other outdoor activity you choose to do when it’s a little hotter outside.

References:

1. University of Connecticut. Korey Stringer Institute. Heat Acclimatization.
2. Johnson, J. Exercise in a hot environment: the skin circulation. Scand J Med Sci Sports. 2010 Oct;20 Suppl 3:29-39.
3. Mayo Clinic. Healthy Lifestyle: Fitness. Heat and exercise: Keeping cool in hot weather
4. Peterkin, N., et al. What Is the Best Practice for the Treatment of Exertional Heat Illnesses (Heat Cramps, Heat Syncope, Heat Exhaustion, and Exertional Heat Stroke)? Athletic Training and Sports Health Care. 2016;8(3):97-99.
5. Periard, J., et al. Cardiovascular adaptations supporting human exercise-heat acclimation. Autonomic Neuroscience. Volume 196, April 2016, Pages 52-62.
6. Periard, J., et al. Adaptations and mechanisms of human heat acclimation: Applications for competitive athletes and sports. 2015. Volume25, IssueS1: 20-38.
7. Racinais S., Sawka M., Daanen H., Périard J.D. (2019) Heat Acclimation. In: Périard J., Racinais S. (eds) Heat Stress in Sport and Exercise. Springer, Cham.
8. Casadio, J.R., Kilding, A.E., Cotter, J.D. et al. From Lab to Real World: Heat Acclimation Considerations for Elite Athletes. Sports Med (2017) 47: 1467.
9. Tyler, C., et al. The Effects of Heat Adaptation on Physiology, Perception and Exercise Performance in the Heat: A Meta-Analysis. Sports Medicine. November 2016, Volume 46, Issue 11, pp 1699–1724.