How Hot is Too Hot?

Tour of California palm springs heat

Anyone for tennis? Players in the Australian Open are getting heatstroke on court and next week sees the Tour Down Under start in Adelaide where it’s even hotter.

Racing in high temperatures brings a new set of challenges and some solutions are set out below. Can it get too hot to race?

First some basics. The temperatures quote on TV are normally the shade temperature and measured according to a strict protocol but the road cyclist has no Stevenson screen which explains why the temperature measured on the road is often hotter than the weather forecast.

Why is the road even hotter?
A black strip of tarmac absorbs the heat from the sun very easily and by the time the race starts the road surface can easily reach 50-80°C (120-180°F). Enough to fry an egg.

With the road so hot, the air above gets heated immediately. So when the temperature in the shade is 32-40°C (90-105°F) it’s common for the cyclist to face infernal air temperatures of 50°C (120°F) and more. If the air above the road feels like riding in a hair dryer, it’s only the start of the cyclists problem with heat. In addition to the ambient temperature there is radiation. Heat is radiating directly from the tarmac and you can add the sun’s rays too.

How to keep cool?
Ride. Unlike a tennis player, the mere act of pedalling ensures a breeze, meaning you can race in conditions where a tennis player or a marathon runner could not. The breeze itself does not cool, it is the evaporation of sweat. With exposed limbs and light fabrics – think Chris Froome’s racey mesh – the road cyclist can let the evaporation effect keep the body cool, or at least functioning, on all but the hottest of days.

All this depends on a breeze but start climbing and your speed drops off as the effort increases. Worse if there’s a slight tailwind you’re travelling at a similar speed as the air meaning the rate of sweat evaporation slows right down. Unlike Lee ‘Scratch’ Perry when it’s too hot, you won’t cool down on the hilltop.

Sweating means a lot of water loss but your body also uses the lungs to cool. When it’s cold you can see your breath condense but when it’s hot you’re losing even more moisture with every breath only you can’t see it. It’s often a forgotten aspect of water loss.

Some riders have an advantage too. A large surface area is better meaning the more skin you’ve got relative to your bodyweight then the more sweating can help. There’s more to it but in simple terms I’d say Chris Froome and Nairo Quintana both have an advantage in the heat over a more classically-built rider like Vincenzo Nibali or Roman Kreuziger.

It looks very hot in Adelaide right now but the peloton can experience high temperatures in the northern hemisphere too. The 2010 Vuelta was a hot one and on one day, teams were handing out 240 bottles a day: on average more than 25 per rider. Of course it depends what is done with the bottles, whether they are used for drinking or get used to douse the rider in water. Last year’s Tour of California saw temperatures of 115°F (46°C) reported on the stage to the Palm Springs Aerial Tramway and exhausted riders riders were collapsing in the heat after the long climb to the finish line.

Cold or hot?
It’s said Bedouin tribes in the Arabian deserts often take warm drinks despite the heat but I wonder if they just need to boil water to keep it clean?. A cold drink on a hot day can be the stuff of fantasy as the rider toils on a hot road. But the sudden ingestion of cold water can cause trouble for stomachs, whether cramps or digestive problems. But a cold drink can help bring the core body temperature down so it’s a question of what works for different riders.

A clever team will weigh riders before and after on hot days to get a quick take on dehydration. If a rider loses too much water then this reduces performance but at the same time it’s hard to constantly drink on the bike for hours. As fatigue sets in, drinking has to become a more concious effort. Here some try a mix of different drinks, plain water, then fruit juice and some with electrolytes, and when all else fails, a can of Coke emerges from the icebox in the team car. If all else fails…

Some teams have been experimenting with ice vests, waistcoats lined with pockets containing a gel that has been in the freezer. These have been used for “warm-ups” prior to the race, the idea being that the rider spins the legs on a trainer but the vests are used to keep the upper body at a more acceptable temperature. But Sky and Garmin have tried adapted versions during mountain stages, a high tech version of the old-school trick of putting sponge under the jersey, behind the collar, so that it drips water.

Adaptation also helps. Riders can get used to the heat, whether from a week’s stay somewhere hot or with more unconventional means. Bradley Wiggins rigged an indoor trainer in a shed and used heaters to recreate the warmth of Spain inside his English home before the 2011 Vuelta.

Stopping a race doesn’t mean a rider cools down, especially as the finish line is often bustling and hot and the rider is standing in sweaty, salty clothing. Some teams are using static trainers to cool down but before this they’ll have a cool drink, maybe a wipe with a damp towel and other means.

It can take longer to cool down properly. A cold bath is a simple remedy to help bring down core body temperatures. Teams use ice baths and and even cryotechnology. The aim of these techniques is to help swollen muscles but the literature is inconclusive, what is more obvious is riders reporting they feel cooler and even sleep better for it.

There are more direct health risks. Melted tarmac can be a problem too. The tar used in road construction begins to soften and slowly the gravel chips sink into the tar and after a while the tar pools on the surface. This dark black material soaks up eat even more easily and liquefies in the sunshine… but only just. But it’s the equivalent of a cartoon character running into a patch of treacle on the road, the dense and sticky tar can catch a rider by surprise on a descent. It was a big factor behind Joseba Beloki’s 2003 crash in the Tour de France. In recent years the Tour de France has deployed a water tanker to spray sections of road prone to melting to help cool the tarmac.

Can it be too hot?
Races can be cancelled because of snow and ice, can they be cancelled because of excess heat? Yes, because the organisers have a duty to protect a rider’s health but there’s little definition to this idea. Setting an absolute temperature is too inflexible, remember the gap between reported and “tarmac” temperatures and there’s also the humidity to account for as this changes the rate of sweat evaporation too. But also the outdoor temperature is not the problem, it’s the inside of your body that’s the issue and a dangerous core temperature comes from exertion, the duration of the effort, dehydration and more. In short it’s feel and a peloton cruising the rolling terrain around South Australian vineyards should feel cooler than one climbing up a mountain pass in California.

A pro race with experienced riders and team cars stocked with drinks is different from an amateur event where perhaps a lower threshold could be considered. It’s up to the commissaires and race doctors to decide on the day but they face a pressured decision with a race organiser desperate for the show to go on.

Finally a word for fans. You know riding a bike brings a cooling effect. But if it’s hot in South Australia next week there’s often no breeze standing beside the road. Sure there’s exertion you can still overheat so be sure to take drinks, wear the right clothing and find some shade.

Tennis can look soft at times with all those regular breaks in play, it’s one of the few sports in the world with chairs next to the field of play so participants can take a break. But playing in the Australian Open probably brings a greater risk of heatstroke than doing the Tour Down Under.

Exercising in the heat can be dangerous but the efficiency of cycling on a road means physical effort can be tolerated because the effort spent making a rider move fast creates a flow of air to help cool the body via the evaporation of perspiration. Modern clothing is a great help.

There are tips and tricks from simple things like a following car stocked with drinks to acclimatisation. ensuring riders often train in warm areas. There are more sophisticated techniques with ice vests and cryotechnology which can help with performance. Sports science literature lists solutions but note teams are often, but not always, ahead of academics.

Some like the heat, some don’t. But it’s a technical challenge to overcome like racing through snow and learning to ride in a crosswind. Setting a safety threshold sounds like a good idea but near-impossible in practice because it’s hard to measure temperature and then we need to account for humidity and then the type of race. It has to be a decision taken on the ground rather than set out in the rulebook.

Further reading:

59 thoughts on “How Hot is Too Hot?”

  1. “It’s said Bedouin tribes in the Arabian deserts often take warm drinks despite the heat but I wonder if they just need to boil water to keep it clean?”

    The esophagus reacts disproportionately to changes in temperature. Drinking cold drink will make your body think it is cold and therefore cooling by sweating will diminish, effectively causing your body to heat up. Drinking warm drink has the opposite effect, and more sweating will make you cool down.

  2. Another huge factor is the humidity. Very often, here in the Mid-Atlantic in the summer, you face the choice of riding when it’s 80 degrees and very humid right around dawn, or 95 and a bit less humid later in the day. I find myself sometimes even feeling cooler in the hotter temperatures later in the day, simply because the sweat evaporates better. Training in the humidity in the morning frequently leaves me feeling nauseated and dripping buckets.

      • Isn’t there a ‘heat index’ that takes into account the air temperature and humidity?

        Another method to cool off is the old panty hose (or stockings) cut up and filled with ice for riders to put inside the backs of their jerseys.

        • There is a “Wet bulb thermometer” that is used at events like marathons to determine if the race goes based on heat. This takes into account the humidity. As the humidity goes up the evaporation decreases because there are more water particles in the air already. As water leaves in evaporation it does a good job of taking heat but if it simply drips off you the cooling efficiency goes way down. There marathon world has good data on what wet bulb temps lead to health risks but there is not the same data for cycling so it’s hard to say from a medical standpoint when it’s too hot.

  3. What is the risk of falling off the bike, then burning your skin on the tarmac? If you dont get up quickly and tarmac temperatures up to 80 degC…

  4. Re humidity: I’m based in Hong Kong, and summer riding is a very humid affair. The sweat does not quite evaporate from the skin, making it hard for the body to thermoregulate effectively and stay within a temperature range conducive to good performance. At the same temperature, it definitely feels much harder than riding in the drier southern Australian summer climate.

    Re tennis: As a former competitive tennis player, I never saw the sport as a soft one. Surely, men’s singles grand slam tennis has got to be the most gladiatorial and lonely form of modern sport? No teammates, can’t talk to coach, no knockout punches… No other way but to grind out the requisite points, games and sets in order to advance to the next round; with every round being a knock-out round.

    • Agreed about tennis, it’s just cyclists sometimes mock the way the players get frequent rests although anyone in doubt should try playing on court in Melbourne right now and see how long their co-ordination lasts.

        • Who needs peak physical condition when at normal temperatures the massive amounts of EPO they’re on sees them through? As far as I can tell tennis has an attitude to doping somewhat on a par with late nineties cycling

  5. Think of the UCI Asia Tour where pretty much every race is run in hot and humid conditions, you’re racing in countries on the equator. I raced in Thailand, Indonesia and the Philippines last year…at Le Tour de Filipinas there were temps hitting 45c and 80-90% humidity. Thailand was no different…what I’ve found works well are enduralytes(or equivalent), 2-3 tabs per hour, cold water over your head and warm water down your gullet. It’s also really easy to forget to eat when you’re racing in those conditions because you’re so focused on fluids, a bit loopy from the heat and certain foods don’t go down so well in the heat, bananas and gels are the way to go.

    • Dont the race organisers in Asia organise spray showers or the riders to pass through/under, at various points on the course? Have I got that right?

      • Sam,

        In some races they have loads of water spraying out of hydrants and hoses at the stage finish, I believe Langkawi has some memorable images from this over the years. A lot of the races, even some of the UCI races, allow neutral water support in the form of scooters carrying and passing water out so no need to go back to the car. Usually you’re drinking 2 bottles an hour and 3 per hour over your head.

  6. “A large surface area is better meaning the more skin you’ve got relative to your bodyweight then the more sweating can help”
    That is not correct – usually body surface area is calculated using i.e. du Bois formula
    BSA (m²) = 0.20247 x Height(m)0.725 x Weight(kg)0.425

    A climber 160cm tall and 50kg rider has as BSA og 1.5 square metres whereas a a classics rider at 180cm and 75kg has a BSA of 1.89.

    Usually hot, humid temperatures favour the smaller athelete with relatively larger surface area compared to their volume than their larger counterparts.

    The works of Timothy Noakes are highly recommended to anybody with an interest in hyper- and hypothermias effect on aerobic performance

      • Basically depends on the stature of the athlete but in conditions with high wet bulb temperature the small athelete has an advantage as the absolute heat loss due to convection and evaporation is restricted. If in doubt, calculate their BSA to predict their performance on hot climbs 😉

      • Broadly speaking, all cyclists are pretty damn thin. Wouldn’t the amount you have to cool down depend on your mass/volume, and the amount you’re able to do so depend on your area? If volume tends to increase proportionally faster than area (cubes vs squares and all that), taller is worse, surely? One of the reasons why Paula Radcliffe could set world records in London’s spring and New York’s fall, but get stuffed by shorter Kenyans in Athens’ or Beijing’s summer?

        • Exactly – a good example is the 1996 Olympics were small runners dominated the marathon field in a hot, humid climate.
          Actually, the result of the 1996 marathon was more or less predicted by “Olympics in Atlanta: A Fight Against Physics” – “Medicine and Science in Sports and Exercise”, 28, 1996

  7. Some people put cold items like ice packs directly on their skin but if the item is too cold it actually has the opposite effect by causing blood vessels near the skin to constrict.

    What are your thoughts on the risk of overdrinking leading to hyponatremia?

    • I’m not an expert so ducked this issue. There seem to be only a few cases of hyponatremia so telling people “don’t overdrink” runs the risk of some people picking up the wrong message and not drinking enough for fear of hyponatremia.

  8. “The breeze itself does not cool, it is the evaporation of sweat.”

    That is wrong. Evaporation is the main factor, but the breeze does cool. The cooling effect is convection at work, it’s proportional to the temperature difference between the rider’s body (37 to 40 °C, see the science of sports article link) and the atmosphere, and also varies with relative air speed.

    • I enjoy Mr Inrng’s explanations very much for their airy grasp of the essentials. In this case it might be slightly more correct to say “The air itself does not cool, it is the evaporation of sweat”.

      A more exact (but still incomplete) statement might be: at higher air temperatures, sensible heat transfer fails to cool the body and may even result in net heat gains. Human thermoregulation in these conditions becomes almost entirely dependent upon latent heat transfer, which is affected by clothing, air and skin temperature, air humidity and natural or forced air convection.

      Isn’t it a mouthful? I prefer Inrng’s style.

        • Not really, wind chill is a way of expressing the potential for increased sensible heat losses due to forced convection (wind). You might think that dry, hot, windy conditions could be expressed in a similar way as, let’s say, a ‘wind bake’ scale, but latent heat (evapotranspiration) kicks in and messes it all up, being quite non-linear.

  9. Another thing that can happen to tar when it gets hot and sticky is this (hopefully the link works):

    This happened to us last year climbing up Lake Mountain last year (near Melbourne, Australia) on a ~40 degree day. We could hear the tar “popping” as our wheels went over it, which was the tar starting to get pulled off the road. Some of it then started to stick to our tyres and it just accumulated until the wheels couldn’t turn anymore, stranding us on the mountain. You couldn’t get the stuff off, either. We ended up having to wait for someone to drive out from Melbourne (2 hours) to come and pick us up.

    • Wow!!!!

      That happened to me recently, at much lower temperatures. Actually, things weren’t as bad as that… but the tar bubbling up did occur over Christmas / New Year in Thredbo, but the temperature’s were only around the 20 degree mark.

    • I’ve never seen it that bad. In melts in France in the summer but curiously much less in Italy, a different mix is used. It can rip the tread off too.

      The Tour de France sometimes deploys a tanker truck to spray the road ahead of the riders so it cools down, it has to be far enough ahead to dry out but close enough to mean the road has cooled.

  10. When I was racing in the lower categories back in the nineties, I used to ride/race an event in Wichita Falls, TX on the hottest day of the year in the last week of August. The event averaged a death every year with the exception of 1994 when there it was an epic heat wave and brutal crosswinds the whole 100 miles. That year , two people died of heat stroke. The temperature was 110 Fahrenheit in the shade. This event draws a huge crowd every year. Anywhere from 17,000 to 25,000 riders.
    That wasn’t the worst one. That honor goes to the 1998 Texas road state championships which were held in west Texas, the temperature was 130F and the race started in the afternoon at noon. That was one of the few times that I got severely sunburnt.

  11. I race with the AVCC in Oz and they have the rule that says when the temperature is over 35c the race distance is reduced and when its over 40c the event is cancelled!

    Seems very sensible to me but then of course we are not professionals and we are old guys!!!

  12. The forecasts are for it to cool down to just over 30 Celsius for the first few days of the TDU.

    I’m in Melbourne at the moment, and while it’s bloody hot, the humidity is very low and it’s actually reasonably bearable. And there’s usually two or three hours around sunrise where cycling is actually quite pleasant in the mid to high twenties.

    I assumed that if it gets really hot there will be a tacit agreement through the peloton to back it off a bit, particularly for the flat TDU stages which are guaranteed to end in a sprint anyway. Is this not the case?

  13. I like the photo of camaraderie between the Movistar and Rabbobank (now Belkin) rider. Especially because those teams don’t like each other!

    • Maybe a breakaway, where they had to cooperate?
      And the first photo is one of Leopold Konig after the hottest stage in California 2013, which cost him GC chances. Statistically, riders from north and middle do withstand hot worse. I wonder, if this has impact e. g. on the decision whether to ride TDU or San Luis. The latter takes place at higher altitudes (besides being better suited for climbers).

  14. I really enjoy riding in the heat and as I am in Greece the usual average temperature fro about 5-6 months a year is 30 degrees which means about 35-40 on the road (according to my garmin)… But nothing beats riding for 3 hours with 40 degrees and then jumping in the sea for a swim!!!

    Nevertheless, when in July and August the temperature goes up then it is difficult to ride and sometimes difficult to breathe, I would say it needs the same panache as when riding in extreme cold (near freezing) and all comes down to what you are used to and what you have trained for..

  15. How hot was it at Mont St Michel, when a spectator helpfully threw water over Cav, only for him to realise it was urine when he tasted it !

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