How to Exercise Safely and Effectively in the Heat
As temperatures soar during the summer months, training in the heat brings its own set of challenges. High temperatures can make workouts feel significantly harder and can also impact your performance and recovery. So, how can you stay cool, avoid overheating, and continue to train effectively?
The key lies in understanding how your body responds to heat — and then applying smart strategies to stay safe, hydrated, and efficient.
What Happens to Your Body in the Heat?
Exercising in hot weather places extra stress on your body. Both the exercise itself and environmental factors — such as high air temperature and humidity — cause your core temperature to rise. When this happens, your body must work harder to stay cool and maintain normal physiological function.
To help regulate temperature, more blood is diverted to the skin to support sweating and heat loss. While this cooling mechanism is essential, it comes at a cost: with less blood available for working muscles, your heart rate increases to compensate, and you may fatigue faster.
Sweating is the body’s primary way of shedding excess heat. As sweat evaporates from the surface of your skin, it cools you down. However, sweat loss also reduces blood volume and hydration status, which can impair cardiovascular efficiency and reduce power output — particularly during prolonged or high-intensity sessions.
Dehydration and Performance
When exercising in the heat, fluid loss through sweat can be substantial. Dehydration not only increases your perceived effort and reduces performance, but it also puts you at risk of heat-related illnesses.
A drop in performance is typically noticeable when fluid loss exceeds 2% of body weight. For a 70kg athlete, that’s around 1.4kg of fluid — or about 1.4 litres of sweat. Even mild dehydration can impair performance, with some studies showing a 5–20% reduction depending on exercise intensity and environmental conditions.
If your core temperature climbs above 39°C, you’re at risk of heat-related illness — ranging from heat stress and heat exhaustion to life-threatening heatstroke.
Top Strategies for Staying Cool While Training
Shorten or reduce intensity – Opt for shorter or lower-intensity workouts on extremely hot days. Save harder efforts for cooler conditions if possible.
Train early or late – Schedule sessions in the early morning or evening to avoid the hottest part of the day (typically between 11am and 4pm).
Seek shade when outdoors – Run, ride or train in shaded areas to reduce direct sun exposure.
Pre-cool your body – Sip an ice-cold drink or slushy (crushed ice + water) just before your workout to lower your core temperature.
Use surface cooling – Pour water over your head, neck, or arms to promote evaporative cooling.
Get creative with ice – Tuck ice cubes into a cap, neck scarf, socks or jersey pockets to help cool blood vessels close to the skin.
Hydration: Do You Need to Drink More?
Hydration is a cornerstone of heat management. Keeping well-hydrated helps preserve blood volume, supports sweat production, and reduces cardiovascular strain.
For sessions under 2 hours: listen to your thirst. There's no need to drink excessively — overhydration can dilute sodium levels in the blood (a condition known as hyponatremia), which can be dangerous.
For longer workouts or events (>2 hours), especially if you sweat heavily: follow a proactive hydration strategy. Aim to replace most (but not all) of your sweat loss to prevent dehydration while still allowing your body to manage fluid balance naturally.
A practical target is to keep fluid loss under 2% of your starting body weight. Weigh yourself before and after training to monitor your sweat rate and adjust your intake accordingly.
What About Electrolytes?
You lose electrolytes — particularly sodium — when you sweat. But for most workouts under two hours, your body has sufficient stores to cope, and you don’t need to supplement.
For longer sessions in hot conditions, or if you’re a salty sweater, consuming some sodium (e.g., through sports drinks, electrolyte tablets, or salty snacks) can help maintain fluid balance and improve long-term recovery. However, there’s little evidence that sodium intake improves performance during the session itself.
Cramps are often blamed on low electrolytes or dehydration, but recent research suggests the causes are more complex and may involve neuromuscular fatigue. Replacing sodium may help in some cases, but it’s not a guaranteed solution.
Training Your Body to Handle the Heat
If you’re preparing for an event in a hot climate, heat acclimation training can significantly improve your performance and reduce your risk of heat-related problems.
Heat adaptation involves regularly raising your core temperature during training over a sustained period, allowing your body to become more efficient at cooling itself.
Heat adaptation tips:
Start 2–3 weeks before your target event.
Train in warm conditions, or simulate heat by wearing extra clothing during workouts.
Alternatively, sit in a hot bath (~40°C) for 30–45 minutes immediately after a workout to raise your core temperature.
Aim for a 1.5°C increase in core temperature during these sessions, repeated daily for 10–15 days.
Signs You’re Becoming Heat Adapted
Lower resting and exercising heart rate for the same effort
Earlier onset of sweating
Increased sweat rate
Better tolerance of heat and reduced perceived exertion
These adaptations will help you feel more comfortable in hot conditions and maintain your performance for longer.
Final Thoughts
Training in the heat doesn’t mean you have to compromise your fitness goals — but it does require extra care and attention. By learning how your body responds to heat and putting the right strategies in place, you’ll be able to stay safe, optimise performance, and even enjoy your summer workouts.
Key takeaways:
Adjust intensity, duration and timing of workouts in hot weather
Hydrate according to thirst and sweat rate
Use cooling strategies to manage body temperature
Be cautious with electrolyte supplements — they’re not always necessary
Consider heat adaptation if racing in warm climates