Training sessions in the heat

With sunshine and warmer temperatures forecast for much of the UK, how can you still perform when the mercury rises? The GB Rowing Sports Science Team provide advice

Despite many athletes completing well-practised race or nutrition plans, fewer athletes have a strategy to combat the heat during training and competition periods which may be detrimental to performance (see reference 1).  Temperatures of more than 25°C may have a significant impact on how we feel and perform during exercise and competition. So, as the weather gets warmer, how can you ensure that you are best prepared to thrive in the heat?

Stay hydrated

Sweating plays an important role in cooling the body during exercise. Sweat rates can often exceed 1-2 litres per hour in the heat and, if fluids lost through sweating are not replaced sufficiently, then dehydration will occur. Even if you lose as little as 2% of your body weight in fluids, this can impair your ability to cool down and perform to your best.

What to do when training?

Before exercise: Consume approximately 500ml of fluid every 2-3 hours before training or competition.

During exercise: Be prepared and ensure that you have sufficient fluid for sessions. Losses in body mass through sweating should be minimised by drinking little and often during a land or water session. Sodium is the main electrolyte lost in sweat and should be replaced during prolonged sessions (over an hour) in the heat. Add a quarter of a teaspoon of table salt per litre to your drink or additional salt with your food to replace these losses and aid  fluid retention.

Afterwards: Weigh yourself before and after exercise to find your estimated sweat rate. This will determine how much you need to drink in order to replace lost fluids. See how to calculate this below.

Replace 120-150% of the body mass that you have lost in sweat within the first 1-2 hours of stopping exercise. One kg of body mass equates to one litre of fluid and should be replaced by drinks containing electrolytes, carbohydrates and protein – i.e. water, juice or milk.

Get acclimatised

In order to cope with an increase in temperature, your body will make some specific physiological changes to regulate its temperature and perform at its best. The most noticeable adaption is an improved ability to remove body heat through sweating (see reference 2). This is primarily achieved by an earlier onset of sweating and higher sweat rates.

Appropriately planned – and targeted – heat acclimatisation can improve maximal and submaximal performance in hot and in temperate conditions. Maximal is where you train to your maximum and exhaustion; submaximal where you train below your maximum.

Weigh yourself before and after exercise to find your estimated sweat rate

So how do you improve  your performance?

Safety first. Build up exposure to the heat gradually to adapt to the new conditions. Keep your perceived effort easier when it’s hot and save your longer, or more intense, sessions for cooler times of the day.

Targeted heat sessions should last for at least an hour to induce sweating and increase body temperature.

Full acclimatisation can be achieved within two to three weeks, depending on the temperature, the frequency and duration of exercise.

Consider wearing extra layers during your cooler workouts to stimulate the effect of a warm environment or turn off any fans to minimise evaporative cooling through the air flow.

Stay cool

While targeted sessions in the heat may be beneficial you should plan to cool off during key performances. Cooling strategies before, during and after exercise have the potential to offset detrimental increases in body temperature.

Six tips for keeping cool

1. Avoid unnecessary exposure to the sun. Complete your warm up and cool down in the shade where possible.
2. Wear sun cream (SPF 30+) to protect you – sunburn decreases cooling efficiency and can be detrimental  to performance.
3. Choose light-coloured and breathable clothing.
4. Lower your skin temperature by soaking a T-shirt in cold water and  re-soak every 5-10 minutes.
5. Use a fan or your hand to create a breeze to help your skin cool down.
6. Place cooling towels or ice packs on your neck and on major muscle groups or submerge your hands/arms/ legs/ankles in cool water.

Sunburn decreases cooling efficiency and can be detrimental to performance

How to calculate your sweat rate

1. Go to the toilet.
2. Weigh yourself before exercise, wearing minimal clothing.
3. Do a 60-minute training session consuming fluid as normal.
4. Wipe away sweat from skin and hair.
5. Weigh yourself after exercise, again wearing minimal clothing.
6. Record how much fluid you consumed during exercise.
7. Then calculate as below:
   (pre-session weight in kg) – (post-session weight in kg) + (fluid consumed in kg) = sweat rate in litres per hour (e.g. 80 – 78.8 + 0.8 = 2 litres/hour)

Take it further – the references

1. Heat acclimation improves exercise performance by Lorenzo S. et al. Journal of Applied Physiology, 2010 Oct; 109, pp1140-1147.
2. Consensus recommendations on training and competing in the heat by Racinais S. et al. Scandinavian Journal of Medicine & Science in Sports, 2015 June; 25, Suppl 1:6-19.

This article was written by Sarah Moseley, Sport Scientist (physiology)
Illustration by Jo Scales