Is it safe to exercise in the heat?

Is it safe to exercise in the heat?

When it comes to summer I often wonder how people do it.

Exercise in the heat. 

Up to 35-40 degrees at the height of summer.

In the heat of summer, just walking the dogs I build up a sweat, especially with the added humidity of a Sydney summer. That is why we always aim to walk the dogs early in the morning and later in the day.

Once you take them out inside that window of higher heat, they really start to pant and if I am not careful they will make a mad dash for the Bay just so they can cool off!

Luckily for us we don’t have to deal with the fur coats.

So when I see people running around the Bay during the height of heat and summer, I wonder:

Why do they do it?

How do they do it?

And is it safe to exercise in the heat?

When it comes to regulating our temperature, it’s a bit different from our four-legged furry friends, although there are some similarities.

When dogs are hot, they pant, drink more water and search out for ways to cool themselves – in the water, the shade or lying on a cold floor.

Woman leading exercise class outside

What is Thermoregulation?

Thermoregulation is the regulation of our core body temperature.

Our core temperature is regulated to 36.5 – 38.5 ℃, but may be elevated when exposed to extreme conditions. In well-trained athletes, body temperature can reach 41.5 ℃ without any acute or long term detrimental effects.

Our resting core body temperature can vary depending on:

  • Age
  • Sex
  • Ethnicity
  • Ambient temperature
  • Dew point
  • Time of day
  • Month of year
  • Training

Unlike our body temperature, our skin temperature is not regulated, but acts as an interface with the environment.

Skin temperature varies across the body in response to the thermal environment. Skin temperatures can be categorized as:

  • Cool (< 30℃)
  • Warm (30-34.9℃)
  • Hot (>35℃)
Woman in white activewear doing mat pilates exercise in front of textured concrete wall

What is the physiological impact of exercise in the heat?

By exercising in hot weather, you are putting extra stress on your body.

The degree of physiological strain on your body, depends on your metabolic rate and capacity for heat exchange.

Your metabolism increases 5-15X the resting rate to provide enough energy for exercise. Up to 70-100% of that energy is released as heat and needs to be dissipated to maintain your core temperature.

Your acclimatization state, aerobic fitness and hydration level will determine how effectively you can regulate your body temperature.

When you are aerobically fit, acclimatized to heat and fully hydrated your body will store less heat and you will be able to perform optimally during exercise-heat stress.

When exercising in the heat, your body increases blood flow to your skin to help cool itself. This leaves less blood for your muscles, which in turn increases your heart rate.

With higher levels of humidity, there is the added stress, as your sweat may not readily evaporate from your skin, one of your body’s innate self-cooling mechanisms, pushing your body temperature even higher.

In addition to the body’s physiological responses we can regulate our temperature through conscious behavioral adjustments or cool-seeking behaviors such as:

  • Exercising in the shade
  • Drinking cold beverages
  • Pouring water over one’s head
  • Wearing light coloured clothing
  • Adjustmenting work rate during exercise in the heat
principles of strength training

How do different environmental conditions impact our body when exercising in the heat?

The conditions in which we exercise have a big impact on the degree to which our natural physiological systems will be stressed with exercise in the heat.

Ambient Temperature

In the Sydney summer months, those exercising the heat, may have to deal with ambient temperatures of over 40 degrees.

During exercise, when ambient temperatures are higher than skin temperature, your body gains MORE heat.

In environments with high ambient temperatures and low humidity, there is more evaporative heat loss as sweat and moisture can more easily evaporate. Thus, in Sydney, where we have more humidity, there will be LESS heat loss through evaporation (relative more heat gain).


High humidity impacts one’s ability to effectively and efficiently evaporate sweat from the skin because of the small difference in moisture between the skin surface and the environment.


When exercising, air flow results in convective heat exchange. The movement of air assists in heat loss as it removes the layer of moisture that may stagnate across the skin.
Older man playing tennis

Are there special considerations for exercise in the heat?

Wear Proper Clothing

Your clothing acts as a barrier between the skin and the environment, changing heat exchange properties relative to the environmental conditions.

Thus, the material and fit of clothing can impact heat strain during exercise as it often reduces heat dissipation and promotes heat conservation. Thus, when it comes to the clothing we wear during exercise in the heat, we want less insulation, low moisture resistance and low water absorption.

When water is trapped it clothing, it can not evaporate and this does not help cool the body

Lastly, it is not may not be the color of our clothing which reduces heat strain, but the reflective properties of the garment when exercising in direct sunlight.

Increased Age

Individuals over 60 often have:
  • Lower resting body core temperature
  • Reduced dilation of blood vessels in the skin
  • Less effective sweat response
  • Decreased thermoreceptor sensitivity
However, fit older individuals do retain a better ability to regulate body temperature and have improved this capacity with training.

Aerobic Fitness Level

By engaging in regular endurance exercise one will have better aerobic fitness, which has been shown to enhance one’s ability to dissipate heat. Aerobic training helps:
  • Activate dilation of blood vessels within the skin at lower body temperature
  • Increase skin blood flow for a given core temperature
  • Reduce internal temperature threshold for onset of sweating

Exercise in the heat: The Tokyo Olympics Study

A study by de Korte et al looked at simulated Tokyo environmental conditions on exercise performance and the body’s thermoregulation responses in a group of elite Dutch athletes.

Tokyo’s summer is similar to ours in Sydney, with temperatures of > 30 degrees and humidity of +/- 70%. Researchers thought this would result in challenging conditions for the athletes.

A combination of heat stress from the environment and exercise-induced heat production would likely surpass the innate heat-dissipating capacity of the body. The resulting exercise-induced core temperature rises were postulated to hinder exercise performance and increase risk of heat exhaustion and heat stroke.

What did they find?

  • Increased exercise-induced core body temperature (moreso in endurance athletes)
  • Perceived heat discomfort in power athletes
  • Dramatic loss in exercise performance, independent of sport

They concluded that the Tokyo environmental conditions would have a significant impact on the thermoregulatory responses and performance capacity of elite athletes. However, the magnitude responses were highly variable amongst individuals.

Dog swimming exercise in the heat

Heat Related Illnesses

Normally our skin, blood vessels and perspiration levels will adjust to the heat. However, these systems can fail when exposed to higher temperatures and humidity for prolonged periods with increased sweating and loss of fluids, leading to heat-related illnesses.

Heat-related illnesses include:

  • Heat syncope and exercise-associated collapse: A feeling of lightheadedness or fainting caused by higher temperatures. Occurs after exercise, such as a long run, if you stop running immediately after a run and stand without moving.
  • Heat Exhaustion: Body temperature rises to 40℃. Associated with nausea, vomiting, weakness, headaches, fainting, sweating and cold, clammy skin. Untreated, can lead to heat stroke.
  • Heat Stroke: A life threatening condition when your core body temperature exceeds 40℃. Your skin may be dry from lack of sweat or moist. Symptoms include: confusion, irritability, headache, heart rhythm problems, dizziness, fainting, nausea, vomiting, visual problems and fatigue.

With exercise in the heat, you need to watch for signs and symptoms of heat-related illness to avoid a medical emergency..

  • Muscle cramps
  • Nausea
  • Vomiting
  • Weakness
  • Fatigue
  • Headache
  • Excessive swearing
  • Dizziness, lightheadedness or fainting
  • Confusion
  • Irritability
  • Low blood pressure
  • Increased heart rate
  • Visual problems

If you develop any of these symptoms, you must lower your body temperature and get hydrated right away. Stop exercising immediately and get out of the heat. If possible, have someone stay with you who can help monitor your condition.

Female surfer exercise in the heat

How can you exercise safely in the heat to reduce the impact of heat stress

Heat acclimatization and cooling strategies are effective tools to optimise exercise performance in the heat and mitigate the risks of heat stress on the body.

Thus, those that have trained to exercise in hotter conditions will tolerate it better than those who have not.

So, to answer the question posed in the title of this blog, yes it can be safe to exercise in the heat, however some are better suited or more adapted to exercise in the heat.

Caution should be taken.

Here are a few tips to exercise safely and avoid heat-related illnesses.


If you are used to exercising indoors or during cooler temperatures, take it easy the first time you exercise in the heat. As your body gets used to it, gradually increase the length and intensity of your workouts.

Know your fitness level

If you are unfit or new to exercise, you should be cautious when exercising in the heat as you will have a lower tolerance to the heat. Keep your exercise intensity low, workout sessions short and take frequent breaks, as needed.

Proper hydration

Dehydration is a key factor in heat-related illness. Staying hydrated will help your body sweat and cool down. Don’t wait until you are thirsty.

For more intense exercise, you may want to go for a sports drink that helps to replenish your body’s natural electrolytes (sodium, potassium, chloride). Avoid alcohol as this leads to more dehydration.

Check the temperature

Check the weather forecast and if you can pick a cooler time of day to exercise. Avoid the midday sun!

Dress appropriately

Clothing should be lightweight, loose fitting and breathable. This assists in the evaporation of your sweat and keeps you cooler.

Understand your medical risks

Certain medical conditions can increase your risk of a heat-related illness – it may be best to talk to your doctor about this and know our precautions.
Female runner looking at the beach


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