Running or working out in the heat comes with its own set of challenges. Your typical workout can feel significantly harder when you’re contending with a high heat index, which is a metric that takes into account the air temperature and humidity.
Suddenly, your normal easy pace can feel like a challenging slog, causing you to breathe harder, sweat profusely, and, most notably, see a spike in your average heart rate during the run compared with that same pace and perceived effort level on a mild day.
Although it’s undeniable that you certainly sweat more when working out in the heat, and it can feel like your body is working way harder, do you burn more calories in the heat?
Furthermore, do you burn more calories in the cold or heat when working out?
In this article, we will discuss the impact of running in the heat and the number of calories you burn, looking at whether you burn more calories running in the heat or cold weather.
We will cover:
- Do You Burn More Calories In The Heat?
- Do You Burn More Calories In The Heat Or Cold?
Let’s jump in!
Do You Burn More Calories In The Heat?
Before we look more specifically at whether you burn more calories in the heat or the cold, it’s probably helpful to briefly touch up on why this might matter.
For one, many people are interested in exercising for weight loss, so knowing how the temperature affects your calorie burn might be a motivating factor to get your workout in, even if it is unseasonably hot or dreadfully frigid outside.
For example, if the winter winds are blowing and the temperatures are cold, but you know you’ll burn more calories exercising in the cold, you might just get a little boost of motivation to get your workout in.
Additionally, if you burn more calories in the heat or the cold, it can affect your fueling strategy during endurance workouts. You might need to take in not only more fluids to stay well-hydrated when exercising in the heat but also more calories to stay well-fueled and prevent bonking.
Do You Burn More Calories In The Heat Or Cold?
So, do you burn more calories in the cold or heat when exercising? The short answer is yes. Compared with exercising in a temperate or mild environment, you will burn slightly more calories exercising in the heat.
However, this difference is generally relatively minimal.
The bulk of any perceived “weight loss“ after working out on a hot and humid day is due to water loss from excessive sweating and increased respiration (as you breathe faster and harder, you expel more water vapor through your nose and mouth).
Even if you try to stay on top of your hydration needs, it can be difficult to keep up with your sweat rate, resulting in a net water loss that appears as body weight loss on the scale after exercising in the heat.
Technically, you do burn more calories exercising in the heat, but this difference is typically not significant enough to amount to much weight loss, even over time.
The body always wants to maintain homeostasis, and one of the more tightly controlled factors is your core body temperature. Your body employs several thermoregulatory mechanisms to help keep your body temperature within a relatively finite range.
When you are too hot, your core body temperature rises.
Any time you exercise, your body temperature increases because your muscles generate heat as they contract.
So, when you are exercising in an already hot environment, your body temperature can increase rapidly and exceed the “safe“ range.
As such, the body doubles down on the thermoregulatory mechanisms that are normally initiated during exercise to cool your body down.
The two primary thermoregulatory regulatory mechanisms that kick in are sweating and increased blood flow to the skin.
Sweating helps dissipate excess body heat because as sweat droplets accumulate on the surface of your skin, excess heat energy from your body is used to evaporate the sweat, turning the liquid sweat droplets into water vapor.
This process is known as evaporative cooling. In order for the sweat glands to produce and excrete sweat, energy is required, so calories are burned.
Additionally, another thermoregulatory mechanism to help bring core body temperature back down is to increase cutaneous blood flow, for the amount of blood that is circulating to your skin.
This requires your heart to beat faster and harder (increasing cardiac output) to circulate more blood to the skin. This added workload on the heart further increases caloric expenditure in the heat.
The other thing to keep in mind is that although you burn more calories in the heat initially, your body can acclimatize to different temperatures and environmental conditions with repeated exposure.
Therefore, after several weeks of summer running, your body will become more accustomed to the heat and more efficient at regulating your temperature. Studies suggest that heat acclimatization happens after about 14 days.
This means that it will take less effort and will burn fewer calories to exercise in the heat with these adaptations.
The other thing to keep in mind is that many people are unable to (or shouldn’t for safety reasons) exercise as long or as intensely in the heat as they would otherwise in a more comfortable temperature or environment.
For example, imagine that you normally run 45 minutes a day and cover five miles (9 min/mile pace), but you do heart rate training, so you are focused on keeping your heart rate around 75% of your maximum heart rate during this workout.
On a very hot day, you might decide that it’s really only safe to go out for 30 minutes.
Plus, because your body is working harder to keep you cool in the heat, your exercise heart rate will be higher at the same pace. Therefore, if you are trying to stay at that 75% maximum heart rate number, you will have to slow your pace down. Now, instead of running 5 miles at a 9-minute pace, you might only run 3 miles at a 10-minute pace in the heat.
Because your workout is two miles shorter, you’ll end up burning fewer calories overall (upwards of 200-300, depending on your body weight).
This is not to encourage you to exercise longer or harder in the heat than is safe to, but it is a reality of one of the impacts of heat on the calories you will burn in your workout.
Just as there are a couple of thermoregulatory processes employed by the body when exercising in the heat to help cool your body down and restore normal body temperature, there is also a thermoregulatory mechanism to increase your body temperature when exercising in the cold or just being in a cold environment: shivering.
Like sweating and increasing blood flow to the skin, shivering is an energy-requiring process, which means that you burn more calories exercising in the cold. In fact, shivering can be a very energy-intensive process and can burn a lot of calories.
Shivering basically involves the muscles involuntarily contracting and relaxing rapidly. Muscle contraction generates heat, which is why, for example, your body temperature increases when you exercise.
Therefore, even though the muscle contractions produced during shivering are not really under your conscious control, your muscles are still consuming energy to support contraction, so you are burning additional calories over baseline.
However, if you are exercising in the cold, the shivering reflex will likely only be initiated towards the beginning of your workout.
As long as you are exercising intensely enough after you have completed your warm-up and moved your body for several minutes, your voluntary muscle contractions will likely increase your core temperature enough to attenuate or mitigate the need for shivering.
Of course, if you are doing very low-intensity exercise in the cold or are in extremely cold conditions, you may shiver much longer or perhaps even throughout the duration of your workout.
For example, if you set up a yoga mat in the snow on a sub-freezing day and work through a gentle Hatha yoga flow, the intensity of your exercise routine might not be enough to generate enough body heat naturally in the environmental conditions to shut off the shivering reflex.
Additionally, if you are not dressed well for the environmental conditions, you might shiver throughout your workout.
If you are wearing too many layers and you overheat and become sweaty, if you do a cool down or drop the intensity of your exercise, the moisture trapped in your clothes can actually drop your body temperature further, causing you to feel freezing and shiver all over again.
Overall, while you technically burn more calories in the heat and cold, the increase is rather negligible in the grand scheme of things.
Make sure you are staying well hydrated and dressing appropriately, and prioritizing your safety. If it’s too hot or cold out to exercise safely, take your routine indoors. You’ll be able to work harder and burn more calories if you’re comfortable!
For more tips and tricks for how to run safely in the heat, check out our guide: Running In Humidity, 10 Tips To Survive It.
