Friday, 24 June 2016

Riding In Hot Weather (2nd Revision)

Heat can be a big threat to performing optimally or, at worst, even finishing. If temperatures reach anything like 37°C it becomes hard to stay cool even if you’re just sitting around. Riding a bike brings a whole host of unique challenges, as exercise speeds up metabolism and produces heat as a side-effect.

As you heat up, blood gets diverted from muscle to skin to allow heat to dissipate into the hopefully cooler air. Sending blood to the skin takes it away from exercising muscles. For a long time, experts believed lack of blood to supply muscle and skin was the reason people performed less well in hot weather.

Athletes have a greater blood volume than non-athletes, which could explain why fitter people seem to cope better in hot weather. The extra blood-flow causes an increased strain on the cardiovascular system, which has to work to keep you cool while also working to keep you moving. This increase in strain means your maximum aerobic capacity — the peak rate at which you can turn fuel and oxygen into energy — is reduced.

Sweating helps cool blood that has been transported to the skin as the evaporation of water takes away energy in the form of heat. So even if surrounding temperatures are above 37°C, you can prevent overheating. Your core temperature can reach around 40°C without causing you harm, but if it climbs any higher, you enter the danger zone where enzymes and other body systems may stop functioning normally.

At what temperature do cyclists begin to experience problems? That is not an easy question to definitively answer, explains Professor Lars Nybo from the University of Copenhagen: “The temperature depends on the exercise intensity, humidity and wind speed, so it’s not possible to provide a set limit.


Fortunately, there are ways to combat the effects of hot weather on riding. A key method is making sure you’re acclimatised to the heat, especially if you’re looking to ride fast. As you acclimatise, your core temperature at rest decreases, increasing the amount of time it takes to get dangerously hot.

A study by Professor Sebastien Racinais published in the Journal of Medicine and Science in Sports and Exercise assessed well-trained participants doing a 27-mile time trial in 37°C multiple times over a two-week acclimatisation period, compared to their performance over the same distance in 8°C.

Their power output was 16 percent lower in the first hot time trial than in the cool, compared to a three per cent reduction in power at the end of the two weeks’ acclimatisation. The average core body temperature of the cyclists after racing was above 40°C, even once they had acclimatised and were able to output more power.

As you get used to being hot, you perform better — but why? There are a number of physiological changes in your body as it adapts to hot weather. The amount of sodium you lose in sweat decreases, helping ensure that you don’t lose too much of this vital electrolyte, while the amount you sweat increases by around 20 per cent, although there are individual differences in both. You also develop improved circulation to skin for heat loss.

As you take on fluids, resting haematocrit — the concentration of red blood cells in blood — decreases as plasma volume (the amount of liquid in circulating blood) increases, meaning there is more blood to circulate to skin and keep you cool, and more liquid to lose as sweat before you become dehydrated.

Research by Anders Karlsen and colleagues at the University of Copenhagen found that it takes around 14 days to fully acclimatise to riding in hot weather, but most of the adaptations take place in the first seven days.

One more, you can try to turn off the air conditioner in your house too :)

Take a bath

If you don’t have time to spend a fortnight getting used to the heat in your race location or you want to be able to ride without suffering on your cycling holiday, a study at Bangor University might provide the answer. Participants who spent 40 minutes in 40°C water after exercising in cool conditions for six days were subsequently better acclimatised to exercise in the heat. How long these adaptations last isn’t fully known. Increased plasma volume seems to last for at least 22 days, although this figure is from a study of untrained people who spent time at 38.5°C.

Go Faster But...

It might sound obvious, but people who are faster than you in a long event have a big advantage — they’re out in the heat for less time so have less time to be affected. The longer you’re in the heat, the slower you’ll get; slower riders effectively go even slower than they usually would.

Another advantage fast people have is the fact they’re moving through the air faster, which will in turn cool them down. The difference here might be significant on the uphill sections where you’re doing 5mph and they’re doing 15mph — enough to produce a cooling breeze. Nybo explains, “As the speed decreases [on an incline] it becomes difficult to maintain sufficient sweat evaporation if the environmental temperature is high, around 35°C.”

Breeze is good but pacing properly is even more important than usual because you need to make sure you don’t bonk and minimise time in the heat. It’s all too easy to set off too hard in the cool of the morning, only to bonk later and really start to suffer as the temperature cranks up. 

Ride to the lower ends of your normal training zones, whether using heart rate or power, and, on long rides, pace ultra-conservatively early on until you have an idea of how your body is reacting to the heat. This especially applies to long climbs where your lower speeds mean you won’t benefit from the cooling effect of a headwind.

Stay fuelled

As your heart rate increases so does the amount of water you lose by breathing. At 140bpm, you lose about 70ml of water per hour in breath. If you become dehydrated, your heart rate will be higher relative to your power output. This is because as you get dehydrated your blood volume falls, which means your heart has to pump more times per minute to get the same amount of blood (and therefore oxygen) to your muscles.

As you sweat, you lose water, but you’re also losing electrolytes including sodium, potassium, magnesium, zinc and calcium. If you don’t stay hydrated, not only are you more at risk from heat exhaustion and illness, and there is some evidence that you’re more likely to suffer from cramp. You can buy ready-made electrolyte formulations in the form of energy drinks which will also contain carbohydrates to keep you fuelled. If you’re fuelling without energy drinks, it may be worth adding electrolyte tabs to your bottles to stay hydrated.

A study conducted in Spain found that Half Ironman triathletes who supplemented to replace 70 per cent of the sodium they lost were around 26 minutes faster than participants who took a placebo instead, so it may be worth upping your salt intake for performance as well as health.

Drink little and often when riding, and make sure that you have plenty of drink with you or know of places on your route where you can obtain more drinks – as if a mid-ride café stop needed an excuse. Packing ice cubes into your bottle before you leave will help keep your drink cool, at least for the first half an hour.

If you’re fit, you can lose two litres or more of fluid every hour through sweat, meaning a certain degree of dehydration is almost inevitable. Meanwhile, your gut can only absorb around 1.4 litres of fluid per hour. It’s all too easy to fail to drink enough when you’re suffering up an alpine pass in soaring temperatures and focused on staying with a group of riders. You should aim to drink at least one litre per hour in hot weather.

The harder you work the more you will sweat, so if it’s really hot and you’re starting to feel it, romping through your drinks, knock off your pace or shorten your ride. And don’t forget in among all the drinking to pay attention that you are eating enough on your ride, too.

Danger Sign

The early signs of heat exhaustion are: heavy sweating; rapid breathing and a fast pulse — all are easy to miss while riding up a mountain. It’s time to get worried when you notice you have stopped sweating, feel nauseous, have a headache and/or feel faint or dizzy.

Severe heat exhaustion can lead to a lack of coordination and confusion. Exposure to extreme heat can be fatal. In a race or completing a certain distance, if you notice any of the warning signs that you’re getting too hot, it’s important to forget about any ideas of going fast and settle into survival mode. Find shade, drink, cover yourself in water and try to find a vehicle to transport you home.

Be Aware of The Condition

Choose a route which has more trees and thus offers more shade. If you cycle in the city or town, pick a route where you can stop at a shop or petrol station to buy some water or energy drinks if you run out

Black strips of tarmac absorb the heat from the sun easily and by the time the day’s stage starts, road surface can easily reach 50-80°C. In turn, the air directly above is heated up like a kettle, so when the temperature in the shade is 32-40°C, that could equate to 50°C or more for the cyclist.

Sometimes, the roads reach such extreme temperatures that the tarmac can become sticky, catching out unsuspecting riders as they descend at 50mph plus. In 2003, ONCE’s Joseba Beloki was in second place overall and descending from Col de la Rochette. The most diligent course recce wouldn’t have unearthed a patch of tarmac softened by the midday sun, which sent Beloki skidding, breaking his femur, elbow and wrist.

Ride Early or Late

Timing is everything. Early morning is the coolest part of the day. The evenings are also a cooler part of the day and are reasonable alternative for those who can't get out in the morning. But if it is really hot, the decrease in temperature in the evening can be minimal. Avoid the hottest part of the day, between 11am and 3pm. With the sun setting later in the evenings this shouldn’t be a huge problem. If you’re going on a day-long bike ride, make sure you get going early in the morning. Be on the bike path half an hour before sunrise. Sometimes a mere 15 minutes’ delay can make the difference between an enjoyable excursion and a miserable exercise in survival. It is better to spend a large chunk of the hottest part of the day chilling in the shade with your friends than grinding away on your bike. You can always continue your ride later when it’s cooler.

What To Wear?


“If it’s very hot, I’ll make sure I’ve got the right kit, something lightweight and breathable that also offers protection from the sun’s rays and wear sun cream with a high SPF to protect anything exposed directly to the sun,” says Cotty.  Covering your skin provides a layer of protection from the sun, giving your body respite from the stress of UV exposure. This means you’re less likely (although not completely immune to) getting sunburnt, but may also keep you cooler.

Wear sunscreen on the exposed parts of your body: arms, legs, face and in particular the back of your neck. The position on your bike means that the area on the front of your legs above the knee and calves will be exposed to sun more than other area of your legs.

A full-length front zip can help you regulate temperature, and a lightweight base layer can also aid the removal and evaporation of sweat from your skin. The breeze you create by riding along has its own cooling effect, and it’s sometimes only when you stop riding do you appreciate exactly how hot it is. A well-fitting pair of shorts are also essential, any rubbing on your delicate parts exacerbated by sweat can cause uncomfortable soreness very quickly. Applying chamois cream before a ride can help.


Black clothing might actually keep you cooler than white because it allows the heat your body produces to escape rather than reflecting it back — potentially one of the reasons Team Sky uses black kit.


Research has shown that while wearing an aero helmet increases head temperature, it doesn’t impact core temperature or power output when cycling in the heat for a short duration. However, there hasn’t been any research into the impact over a long distance. One of the reasons you slow down when it gets hot is that the hypothalamus in the brain stops sending such strong signals to allow muscle to contract when it gets above a certain temperature. Akin to a fuse in an electrical circuit, this gets switched before heat can have a dangerous impact. This happens if the brain alone gets too hot, regardless of core body temperature. If your event is long, wear a vented helmet.

Heart Rate Monitor

It’s a really good idea to use heart rate as a measure of your effort when riding in unusually hot conditions. According to the Racinais study, the athletes involved had a higher heart rate relative to their power output in hot conditions, especially when they hadn’t yet adapted. This means that in the heat your power output will be lower than usual, making a power meter less useful if you’re not acclimatised.

Sun Cream

The dangers of over exposure to the sun are now well known and should be avoided. Use a quality sweat and water resistant sunblock with an SPF of at least 30 and pay particular attention to the back of your neck which is especially exposed on the bike. Don’t neglect your head as it is very easy to get burnt through the vents on your helmet. Look for sunblock with lasting protection and be sure to follow the instructions of when to apply them. With heavy sweating though, even the best sunblock won’t protect you over the course of a long day in the saddle. Carry a small spray bottle in your jersey pockets or saddlebag and re-apply every hour or so.


The intense ultraviolet rays in sunlight damage sensitive cells in your eyes, the cumulative effect of which can result in cataracts, clouded vision and even more horrible stuff that we’re not going to go into here. So make sure your sunglasses have 100% UV-filtering lenses.

"Too Hot to Handle?" Cycling Active, Summer 2016
"Beat The Heat" RideSA 2016/10

Ride On!

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