• Jenny McNamara

Tips for exercising in the heat: lessons from frolicking unicorns

Updated: Jul 13, 2019

Most people love the sunny weather, but if you have a goal race or tough training session planned on a glorious summer's day it can be very unwelcome. You may remember the scenes of carnage as runners took on the 2018 London Marathon in the unseasonably hot 23.2 degree weather- the hottest on record. Spectators loved it, but paramedics had their hands full picking up debilitated runners suffering from heat exhaustion; some after the finish line, others at earlier points on the course.

This weekend we took part in the Moreton Unicorn Frolic- a 12 hour relay race in teams of 3 or 4 runners. I only completed one lap of the 5.25 mile course before taking off my running shoes due to a niggling injury I have been nursing along, while others from Cheddar Running Club managed 3 laps in the sweltering heat.

Mr M cowers in the shade to recover from running in the heat

Poor Mr M, who I passed the squeaky unicorn baton to in possibly the worst transfer since the 2008 US Olympic efforts (I'm pretty sure the US team didn't have a whippet to transfer over too, but I bet they at least had their shoelaces tied up ready to go!) didn't fare too well. In his bid to prevent charring of his Celtic skin, he covered up in tights and long sleeves, and subsequently suffered mild heat exhaustion (pale face, breathlessness, insecure gait, extreme fatigue), taking a good hour to recover.

Wearing too much clothing or the wrong type of clothing increases the risk of heat illness- more on this below. Another runner collapsed out on the course. So how can you race, train or workout safely in the heat? Here are some top tips:

Not a cloud in the sky! Great for sunbathing, less good for exercising at intensity...

1) Be aware that being unfit, overweight, overly motivated, hungover, dehydrated and being older can all make you more susceptible to heat injury- don't be afraid to take it a bit easier or put it off for another (cooler) day.

2) Keep to your prescribed target heart rate- exercising in the heat increases the effort required and the rate of perceived exertion, so even if you are not hitting your training paces or usual workout intensity, you are still working as hard. In races, you might need to modify your goal pace. In workouts, you should consider decreasing the intensity of the workout by reducing the number of rounds, reps or altering the types of exercises.

3) Add rest breaks- even if you would usually work out without breaks between exercises or efforts, it can prevent you suffering in the heat if you let yourself catch your breath and get your heart rate down. You could also change the prescribed exercise, e.g. shorter intervals instead of longer duration efforts.

4) Don't exercise in very humid conditions: As humidity approaches 100%, your body's mechanism of cooling you through evaporation of sweat from the your skin is reduced.

5) Wear appropriate clothing. Yes: lightweight, light colours, loose-fitting, skin exposed

No: Heavy, dark colours, multiple layers, tight fitting, totally covered (Mr M, take note!).

6) Avoid dehydration. On a hot day you will lose more water through sweating as your body attempts to cool itself down (roughly 2 litres an hour on a hot and humid day), so you need to replace this by drinking fluids. You should take a bottle or hydration pack with you on longer runs, but only drink to thirst and not beyond this. In extreme cases, regardless of the physical activity, drinking beyond thirst is the main factor in developing exercise-associated hyponatraemia, which is linked to the development of rhabdomyolysis (Hew-Butler et al., 2017). Salt is also lost via sweat and should be replaced. You can make a simple hypotonic sports drink by mixing together 100ml of squash, one litre of water and a pinch of salt.

7) Don't exercise in the heat! This could mean that you postpone your session for another day, or that you get up early to exercise before it is too hot, or leave it 'til much later in the evening. Contrary to popular belief, exercising in the evening is not associated with poorer sleep quality (National Sleep Foundation Survey, 2013).

In summary, to stay safe and minimise the effects of the heat, make sure you wear the right clothes, adjust the intensity and stay hydrated.

All smiles: Cheddar runners before the race


Tamara Hew-Butler,1 Valentina Loi,2 Antonello Pani,2 and Mitchell H. Rosner. Exercise-Associated Hyponatremia: 2017 Update. Frontiers in Medicine (Lausanne). 2017; 4: 21. Published online 2017 Mar 3. doi: 10.3389/fmed.2017.00021 PMCID: PMC5334560 PMID: 28316971 Available here

National Sleep Foundation Survey, 2013 Summary available here.

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