Road bike training: Cycling in the heat - Hot races: Cooling down during training and competition

Warm, warmer, hotter: cycling against the clock through the shimmering, up to 50-degree Mojave Desert in North America is probably one of the toughest challenges you can face. But sport is also possible in such hostile conditions - if you drink properly, sweat properly and don't cycle too fast. The participants in the Race Across America prove this every year. One person who really loves the heat is Faris Al-Sultan, the 2005 Ironman World Champion. "When it's cold, my muscles suffer and I'm definitely no good," he says. But even for Al-Sultan there are limits: "It was hard to pedal 250 watts in 38 degrees humid heat in Malaysia," recalls the Munich triathlete. Cycling world champion Peter Sagan, on the other hand, is not a fan of the heat. When it was 30 degrees or more throughout the 2015 Tour of Spain, he told the Spanish sports newspaper AS: "I hate this heat, it's ridiculous. The UCI should issue rules so that we don't have to race like this."

So there is an individual component to how well you cope with heat. And there are individual upper limits as to when high temperatures have a negative impact on athletic performance. In the sports science literature, even a cool 10 to 15 degrees is considered optimal for endurance performance.

Air conditioning of the body

What actually happens when we exercise in the heat? The body's own air conditioning system works hard to cool the body: In order for the heat to reach the surface of the body, the skin is supplied with more blood. Accordingly, less blood supplies muscles and internal organs. Pedalling performance decreases, heart rate and carbohydrate consumption increase. We also sweat. Sweat plays a central role in cooling, as the evaporation of sweat removes heat from the body particularly effectively. Millions of sweat pores form a moist film on the skin, whose evaporative cooling can cool the body very well - provided the air is not too humid.

In tropical, humid heat, evaporation no longer works, sweat flows in streams and drips off, the human air conditioning system reaches its limits: sweat that drips instead of evaporating hardly cools at all. Long-sleeved clothing that binds sweat close to the skin and also reflects the sun's rays is therefore advantageous.

In tropical conditions, however, it becomes difficult for the body to maintain a constant temperature of 37 to 37.5 degrees. This is because 300 watts of pedalling power also generates around 900 joules of heat - and this continues to heat up the body if the environment is too warm. If a critical body temperature is reached - which varies from person to person and is between 39 and 41 degrees - the brain reduces the power output to protect the body's protein structures, which start to decompose at 42 degrees. If the body temperature rises too quickly to over 40 degrees, there is also a risk of life-threatening heatstroke.

Thin ones cool down faster

It is favourable for cooling the body if its surface area is relatively large in relation to its volume and mass. Thin and light athletes can cool themselves better than bulky athletes - which means their maximum endurable competition temperature is higher. Sports scientists have even developed model calculations for marathon runners to determine up to what body weight and at what temperature they are able to run world-class times.

You can get used to it

The good news is that everyone can adapt to heat, as numerous studies have shown - although not everyone to the same extent. A Danish study from 2015 looked at the question of how quickly trained cyclists can acclimatise to heat. The study was triggered by the Olympic Games in Rio and the World Cycling Championships in Qatar. The scientists sent nine Danish road cyclists straight from their winter training to Qatar for a fortnight and had them complete their normal, high-intensity training programme in dry heat of around 34 degrees. Tests showed that the riders were already well acclimatised after a week. On average, their time trial performance was only seven per cent below their performance in cool conditions.

As quickly as the athletes adapted to the heat, they lost this ability after returning to cold climes. So if you are planning a marathon in midsummer and don't cope well with the heat, you could
to two weeks beforehand, you could train more frequently in high temperatures. The aim is to raise your body temperature in a controlled manner in order to acclimatise.

This is also possible with artificial heat. Race Across America finisher Michael Nehls took his bike and roller trainer to a public sauna heated to 65 degrees and cycled there once a week early in the morning with low resistance: "At first, I only lasted 30 minutes," he says. "But after six to eight weeks, I was able to cycle for up to an hour and a half until my heart rate had climbed to 160 - my anaerobic threshold at the time." But it wasn't fun. "The feeling in your body is quite strange when you push your heart rate up at low power." But the physical adaptation was successful. In the race, Nehls had no problems cycling at 45 to 50 degrees: "I coped very well with the heat. My main problem was not to consume too many carbohydrates. I therefore alternated between my normal energy drink and salted green tea."

Drinking is one of the most important things in the heat. If you sweat a lot, you need to drink a lot, otherwise your body will dry out. It's not for nothing that the helpers in cycling are also called water carriers. During hard and hot Tour stages, riders drink up to four bottles per hour. Just two per cent fluid loss (of body weight) is considered to reduce performance. However, top runners and professional cyclists have also been found to lose four per cent of their fluid. Where exactly the limit lies is therefore the subject of controversial debate. In any case, ten per cent fluid loss is considered dangerous, with the risk of heat exhaustion. 15 per cent fluid loss is fatal.

Water, sugar and salt

However, the amount of fluid that can be absorbed by the small intestine is limited to one to two litres per hour - which can only be achieved if the concentration of the drink is not too high and the body is not working too hard. If you sweat a lot, you become dehydrated, which can limit your performance during long competitions.
What's the best thing to drink during sport when it gets hot? "Water, sugar and salt - that's the basic formula that has been tried and tested for decades," says TOUR nutrition expert Uwe Schröder from the German Institute of Sports Nutrition. He recommends a pinch of salt per litre and that the amount of carbohydrates should be adapted to the level of exertion (see box on the left). According to Schröder, other minerals play a subordinate role: "Potassium can be helpful over very long distances if your energy reserves are depleted, while magnesium should be taken in small doses." To prepare for the heat, Schröder recommends practising drinking in the weeks before a competition. This means you should drink more than usual - even if it's not hot. The body learns to store more water - and what is too much comes out again.

The best drinking strategy is not to wait until you are thirsty, but to drink half a litre before the start and then regularly drink 200 to 250 millilitres every 10 to 15 minutes, or take small sips even more often. Drinking a lot is also a question of familiarisation and discipline. If you forget to drink, this can favour cramps, especially heat cramps, which plague the whole body. If you notice such signs, you can counteract them by drinking a higher concentration of salt. American scientists have found the following formula to quickly counteract cramps caused by electrolyte deficiency: mix half a litre of carbohydrate drink with three grams of salt and down it. Salt is generally important. If you drink too much pure water, it can even be dangerous because the body is deprived of salt. Some marathon runners have even died as a result of excessive water consumption during competitions.

Cooling relieves

It is also helpful in hot weather to cool the body as much as possible before and during exercise to relieve the circulatory system of this task. Pre-cooling creates a kind of temperature buffer until the critical body temperature is reached. It is a very effective measure for improving endurance performance, especially when training at a moderate level. To cool down, you can use ice waistcoats, cool your wrists in ice water, keep the run-in short or skip it altogether and preferably stay in the shade before the start (see also TOUR 6/2016, page 74). On tours, you can cool down in a mountain stream from time to time - which is not only fun, but also improves your performance on the next climb.
You should also choose your clothing carefully in the heat. TOUR tests have shown that the evaporation performance of cycling underwear can vary considerably. In the heat, a vest that fits tightly and helps to distribute sweat over a large area can support evaporation better than a loose-fitting jersey under which sweat runs uselessly. In very intense sunlight, thin white arm warmers are a tip to protect the skin.

So there is a lot you can do to cope well with training or racing during the next heatwave - even without a drop in performance. Whenever possible, you should get used to the heat in a targeted manner and, above all, listen to your body's warning signs.

Heat experiment

In 2015, Danish scientists wanted to find out how quickly well-trained cyclists can acclimatise to heat and how to measure whether the athletes are already sufficiently adapted. To this end, nine cyclists travelled directly from winter training to Qatar for a fortnight and trained there in temperatures of around 34 degrees. During this training camp, three 43-kilometre test time trials were carried out (after 2, 7 and 14 days) and medical tests were completed beforehand to measure the body's reactions.

As was to be expected, there was a sharp drop in performance in the first heat time trial on the second day. Compared to cool conditions, the riders performed 17 per cent less in the time trial. After a week, the riders were already quite well acclimatised. Their time trial performance was now on average only 7 per cent below their performance in cool conditions. The second week brought comparatively little further improvement. The time trial performance in the heat was 95 per cent of the reference performance at the end.

The medical tests show that the flow of sweat increased by 20 per cent within a week and the plasma volume of the blood increased, as can be seen from the falling haematocrit (proportion of solid components in the blood). According to other researchers, less well-trained athletes can also double their sweat rate within 9 to 12 days. The Danes sweated out an average of 1.6 litres per hour during training and even 2.4 litres per hour in the time trial tests. The sweat itself became less salty in the course of the adaptation.

HOT TIPS

Too much sun is dangerous

Intense sunlight on the head and neck can cause sunstroke. Do not cycle in the sun without headgear if you take your helmet off when cycling uphill. Prolonged exposure to heat can cause heat exhaustion or collapse (dizziness, headache, nausea). A rapid rise in body temperature of more than 3.5 degrees can also trigger life-threatening heatstroke - also recognisable by mental confusion.

Drinking guide

Carbohydrate-rich drinks are the number one fuel for cyclists and are also the right choice when exercising in the heat, but you should add a little salt (1 to 2 grams per litre). The amount of carbohydrate should be a maximum of 80 grams per litre and a maximum of 120 grams per hour, as the body cannot process more. For moderate exercise with a good fat metabolism, the energy concentration can be lower.
concentration can be lower. The fluid intake limit is around 1.5 litres per hour.

Drink for very hot days

Mix 1.5 litres of water with 60 to 90 grams of maltodextrin (long-chain sugar, hardly sweet) and salt (1.5 to 2 knife points), flavour to taste with a splash of fruit flavouring or an espresso. Salt and sugar accelerate absorption compared to pure water.

At the catering station

Isotonic sports drinks and water are usually offered at marathons. If you want to be on the safe side, refuel with water and stock up on gels that you know you can tolerate during training and that contain sufficient minerals (check sodium content!). Unfamiliar sports drinks in large quantities can cause stomach problems.

Query ozone values

On hot days, ozone levels are sometimes high, especially from midday and in urban areas with high levels of air pollution. This can irritate the airways. Exercise in the morning if possible.

Cooling measures

Cool down before heat races - ice waistcoat, dip your wrists in ice water - and ideally also during very hot day tours. Put on a cap and cover your neck and arms. Moist clothing cools better than bare skin.

Water balance

Weigh yourself before and after exercise and determine your water loss or sweat rate. The weight loss plus the drinks consumed on the way correspond to your total fluid loss. Typical sweat rates are between 0.5 and 2 litres per hour. Ideally, your weight loss should be less than 2 per cent of your body weight.

TIPPay attention to the sodium content of water and gels during the race. You should consume at least 400 mg of sodium per hour, which corresponds to 1 g of salt (NaCl).

SHORT & SHORT

Summer heat is nice, but heat means additional stress, reduces performance and can jeopardise your health. To adapt to high temperatures, you should train in hot conditions for at least a week. This can significantly increase your own heat tolerance. Drinking plenty of fluids (up to 1.5 litres per hour) and a little salt will keep you fit.