It’s official: summer is here! But how might the warmer weather affect your fitness routine? Here’s how to stay safe as the temperature rises.
By Dr Courtney Kipps
After the taste of a heatwave in early summer, more and more of us will have turned our thoughts towards how to stay safe while exercising in the heat. While training for a specific organised event is still off the cards for many of us right now, the chance to get outside for some exercise has kept many of us sane during lockdown, so we want to be able to continue, even if the temperatures hot up and the mercury starts to soar.
We spoke with Dr Courtney Kipps, Consultant in Sports and Exercise Medicine at the Institute of Sport, Exercise & Health (ISEH), part of The Princess Grace Hospital (HCA Healthcare UK), for his expert advice on how to exercise safely in warm weather.
How exercising in the heat affects your body
You might expect that warm conditions negatively affect speed and performance over any distance – but that’s not necessarily so.
In hot conditions, endurance performance is generally slower, while sprint (and other short-duration event) performance is slightly faster.
The cumulative heat stress on the body can explain the slower endurance performance, as the body attempts to maintain a stable core temperature.
It’s unclear whether the hot conditions have a direct or indirect effect on sprint performance, or whether it’s merely an association. In intermittent sprint exercise in the heat, players will change their tactics to reduce the higher-intensity sprints and make the most of skill-based performance. This is classically seen in team sports, such as football and hockey, where players will run less and pass more.
Benefits of exercising in the heat
While the thought of lacing your trainers and getting out for a run or other physical activity as the temperature soars might not float your boat, there are actually benefits.
These benefits include:
- Increased vitamin Dexposure
- Enjoyment and psychological wellbeing
- Subsequent increase in fitness
Risks of exercising in the heat
Of course, there are also risks, especially in very hot weather. The biggest risk is exertional heatstroke (EHS). It happens when you’re unable to lose enough heat to compensate for the heat that is generated by your muscles during exercise. Without effective heat loss, the body slowly heats up and will begin to overheat. The body has a delicate system of thermoregulation, to maintain the balance between heat gain, heat loss and heat storage, in order to keep an optimal core temperature for the many physiological functions of the human body. The most effective way to lose heat during exercise is the evaporation of sweat. Exercising in hot and humid conditions means sweat cannot evaporate as easily and therefore you can’t lose heat efficiently. In this situation, unless you do something to improve things, you’re at risk of overheating and developing exertional heatstroke.
Most people will make unconscious or conscious behavioural decisions to maintain their thermal balance. These decisions include:
- Slowing down or even stopping
- Removing heavy clothing
- Moving to the shade
- Pouring cold water over themselves
- Standing in a breeze
In competitive situations – for example, a race – where there are psychological drivers (prestige) and/or external drivers (prize money or selection) to keep pushing hard, the natural tendency to slow down may be over-ridden by the impetus to keep going, putting you at a higher risk of developing EHS.
Tips for exercising safely in the heat
You can reduce the risks of overheating during exercise in different ways, depending on the circumstances:
If the conditions are expected…
If you know what the conditions are likely to be, and you have the time and opportunity to do so, you can acclimatise to the predicted conditions slowly. This means getting your body gradually used to exercising in the predicted conditions. As you do so, your body will gradually adapt to the new conditions in multiple small ways (for example, by increasing sweat rate). These adaptations take at least two weeks and need to be planned carefully.
As an example, we know that the conditions in mid-summer in Tokyo, when the Olympic and Paralympics were due to be held, would be very hot and humid. Athletes were preparing for their events in heat chambers and were expecting to fly out to Japan several weeks early, to give themselves time to acclimatise and get their bodies used to the conditions.
If the conditions are unexpectedly hot and humid, or you don’t have the time to acclimatise, then you would be wise to exercise with caution:
- Don’t push too hard
- Leave the PB for another time
- Listen to your body and slow down if necessary
Instead, plan to enjoy the exercise, rather than taking unnecessary risks and ending up in hospital.
Additional strategies may make small differences, but they are not guaranteed to prevent the risks. These include:
- Drinking ice-cold drinks
- Pouring cold water over your head
- Plunging your hands and feet into cold water
Pre-cooling can also be helpful – think about ways to cool your body before you start your event, for example, drinking ice slurry or putting a cold, wet towel over your head.
Why you shouldn’t drink too much fluid
Drinking cool fluids will help to cool you down, but drinking a lot does not reduce your risk of EHS (the main risk factor is imperfect heat loss, not fluid balance).
On the contrary, drinking too much risks another, equally serious and even life-threatening problem: exercise-associated hyponatraemia (EAH).
EAH can occur in any athlete in any conditions, but tends to occur more in longer events in warmer conditions, where athletes have more time to drink more fluid and may believe they should drink more because of the conditions.
It’s important to note that any fluid (whether it’s water, sports drinks or other drinks) can cause EAH if you drink too much of it.
There is always a lot of debate about what’s optimal hydration for exercise. The reality is that the body is very good at conserving fluid and salts, so you don’t need to drink too much. Your sense of thirst, which has been fine-tuned by evolution over thousands of years, is also an extremely accurate indicator of when and how much you need to drink. Everybody is different, so listening to your body is the best way to decide how much you, specifically, need.