How hot is too hot for fitness classes?

Is it too hot to exercise?

As a general guide, exercising becomes riskier when temperatures exceed 26 degrees Celsius, with a higher risk of heat exhaustion from exercise above 30–32°C. During a UK heatwave, it may be too hot to exercise at full intensity, particularly in poorly ventilated spaces or direct sunlight. Always adjust your workout based on temperature, humidity, and how your body feels.

However, it’s important to remember that extreme temperatures at either end of the scale can impact exercise safety. Just as it can be too hot to exercise, colder conditions can also present risks such as reduced muscle flexibility and increased injury risk. For a full overview of exercising safely in lower temperatures, read our guide on how cold is too cold for group exercise classes.

What temperature should a fitness studio be?

Generally speaking, fitness studios will be operating at 18 degrees Celsius, with gyms being slightly lower. However, if you’re teaching in a community venue, your space may differ due to the multi-function of the room.

It is normal for temperatures to fluctuate slightly in these spaces, especially as people start to work out in them.

Maintaining a safe gym temperature is essential for both performance and safety. As the temperature rises, the body works harder to cool itself, which can impact endurance and increase the risk of heat exhaustion during exercise.

Is there a legal temperature limit?

According to Gov.uk, there is currently no maximum temperature limit. This is where group exercise instructors must understand temperature risks and use their own judgement when planning and running summer classes.

Temperatures between 26-32 degrees Celsius can cause signs of fatigue and exhaustion when taking part in prolonged exercise.

Temperatures above 32 degrees Celsius present risks of heat exhaustion and heatstroke, which must be taken very seriously.

Alpine Trek has a handy tool where you can work out the exercise risk by inputting the air temperature and the humidity to get a reading. Use it for yourself here.

This is often where the question arises: what temperature is too hot to exercise? While there is no strict legal cutoff, many professionals consider anything above 26 degrees Celsius to require significant adjustment to exercise intensity, particularly during a UK heatwave.

Exercising during a heatwave: what to consider

During periods of extreme heat, such as a UK heatwave, exercising during a heatwave requires additional caution. It may not always be safe to run standard fitness classes without adaptation.

Indoor environments can quickly exceed safe levels without ventilation
Outdoor activity increases exposure to direct sunlight
Humidity can make temperatures feel significantly hotter

Signs and symptoms of heat exhaustion and heatstroke

The NHS list of signs and symptoms of heat exhaustion includes:

- tiredness

- dizziness

- cramps in the arms, legs and stomach

- fast breathing or heartbeat

- excessive sweating and skin becoming pale and clammy or getting a heat rash, but a change in skin colour can be harder to see on brown and black skin

Recognising heat stroke symptoms during exercise is essential. Unlike heat exhaustion, heatstroke is a medical emergency and may include confusion, loss of consciousness, or very high body temperature.

Familiarise yourself with the full list here.

Helping someone with heatstroke

If one of your class attendees starts to suffer from heat exhaustion, you should follow the following steps:

Move them to a cool, shaded area.
Ask them to remove unnecessary clothing, such as shoes, socks.
Get them to drink cool water and/or a sports drink.
Spray or sponge their skin with cool water to cool them down. Fan them and where possible, apply wrapped cold compresses to their armpits and/or back of neck.

If in any doubt, call 111.

If the person has not cooled down within 30 minutes, has a seizure, or their symptoms worsen or change, call 999.

What safety measures should I put in place?

All group exercise instructors must do due diligence when taking group exercise classes in the heat. These measures should include (but are not exhaustive to):

- Check PAR-Q forms for any medical conditions that may be affected by heat. Be aware of medical risks as certain conditions or medications can increase the risk of a heat-related illness. Participants should have checked with their doctor before exercising.

- Work with your venue to cool the room. If the room has air conditioning, make sure that is on before your class starts. If not, open windows and doors and make use of fans where possible to circulate airflow.

- Reduce the intensity of your class. Your class intensity shouldn’t be making people suffer in the heat. Look at adapting your movements for the summer weather and adding in extra rest breaks.

- Look for shaded areas. If you’re running outdoor classes, these should ideally not take place in times of peak heat. This is usually between the hours of 11.00am – 3.00pm. The hottest time of the day may vary so check your local weather forecast regularly. However, if this is unavoidable, look for shaded areas and remind class attendees (and yourself!) to wear sunscreen and a hat.

- Stay hydrated. You should drink plenty of fluids when you exercise and even more so in the heat. Remind your participants to do the same and suggest they bring extra drinks with them.

- Know your own limits. You need to understand your own limits and make sure you’re working out within them too.

Encouraging participants to stay hydrated

Staying hydrated is one of the most important ways to reduce the risk of heat exhaustion from exercise, particularly when exercising in hot weather.

Participants should be encouraged to drink water before, during, and after exercise, even if they don’t feel thirsty. Dehydration can develop quickly in warm conditions and may significantly impact performance, energy levels, and overall safety.

As an instructor, you can support hydration by:

Reminding participants at the start of the class to bring enough fluids
Building in regular hydration breaks, especially during higher temperatures
Encouraging participants to listen to their bodies and pause if needed
Recommending additional fluids for longer or more intense sessions

In higher temperatures, hydration becomes even more critical when deciding whether it is too hot to exercise safely, as fluid loss increases more rapidly and can contribute to fatigue, dizziness, and heat-related illness.

Read our blog “6 tips to share with your class members to keep them hydrated” for more information.

Sharing the information

We’ve created social media tiles and a handy factsheet to share with your class members. You can download these easily by accessing the EMD UK instructor resource hub. If you’re not already a member, sign up here to gain access.