When you purchase through links on our site, we may earn an affiliate commission.

Home / Training / Long distance / Racing In The Heat

Racing In The Heat

It's nature that decides an athlete's fate at Kona. Andy Blow looks at the role the elements will play during the race

One element truly dictates the destiny of Kona’s athletes – Mother Nature. Andy Blow examines the issues 1,900+ Iron(wo)men will face on 13 October in this article from the 220 archives

Julie Moss, Chris Legh, Wendy Ingraham, Sian Welch, Paula Newby-Fraser… Over the years, many world-class triathletes have all provided high drama on Ali’i Drive at the end of Ironman Hawaii by staggering, crawling or collapsing within metres of the finish line. In doing so, they kept the race doctors on their toes.Legh outperformed the rest by getting the local surgeons involved to remove a section of his damaged large intestine in an emergency post-race (1997) operation, such was the punishment the race dealt out to his body. After a successful comeback seven years later, when he won Ironman Coeur D’Alene in the USA, Gatorade took full advantage. They used his dramatic story to fill the world’s most expensive advertising slot during the 2005 Superbowl coverage on ESPN to promote how they assisted in his rehabilitation from the Kona A&E dep’t to Ironman podium.

In each case, it was a combination of factors that led to those athletes faltering in the closing stages of such a gruelling event. Glycogen depletion, dehydration and muscular fatigue were significant, but the high temperatures and humidity experienced in Kona certainly played a large part in each of their predicaments.


To stay alive, the human body needs to tightly regulate its core temperature (35-42°C is the range compatible with life) despite huge variation in external temperatures. The average climatic conditions for Kona in October are a daily of high of 30 and a low of 22°C. However, temperatures as high as 34°C have been measured. Humidity comes in at between 50-80% on average and adds to the oppressive nature of the environment. Rather than choosing to sip pina coladas in the shade like any sensible person would normally do when faced with these conditions, the Ironmen and women who take on the World Championships head out for a marathon during the hottest part of the day, straight after a gruelling swim and bike ride.

When exercising, a staggering 70% of the chemical energy consumed in muscular contraction is converted to heat rather than creating movement. Losing this heat to the external environment is essential to keep the core temperature in check and various mechanisms are used by the body to do this. Firstly, blood flow is diverted to the surface of the skin to allow heat from the working muscles to dissipate via convection into the air. This explains why you go red when warming up. As the average resting skin temperature is around 33°C, if exercise is undertaken in air temperatures above this, then losing heat to the air isn’t an option. In fact, the opposite effect takes place and the body gains heat
from its surroundings.


Sweating is the next line of defence as the evaporative effect of sweat vaporising off the skin takes considerable heat away – hence why you feel the cold much more when you’re wet. Sweating works really well when the air is dry, but as the air gets moister and humidity rises, less water can evaporate into it from the body and it simply drips off, taking little or no heat with it. This is why exercising in environments that are both hot and humid is particularly taxing and needs to be approached with care.

In Kona, fewer athletes succumb to heat stroke (the condition that is caused by a core body temperature of over 41°C) on the bike section than on the run. Why? Firstly, the bike ride starts early in the morning when ambient temperatures are lower. Secondly, the evaporation of sweat is increased by the wind speed next to the body. On the bike, even when there’s little wind, the relative speed of air moving across the body means that cooling is more effective than when running. Cooling has been shown to be significantly better when
an athlete is moving at 20km/hr or above, as most are on the bike.

Thirdly, during the bike section the athletes have been racing for less time and are less likely to have become significantly dehydrated. Dehydration and core body temperature have been shown to have a linear relationship, with each 1% of dehydration leading to a core temperature increase of 0.2 to 0.3°C. This is probably because as dehydration lowers blood volume, the potential for heat loss via skin blood flow decreases.

If an athlete does start to overheat and their core temperature rises to around 41°C, they are said to be ‘hyperthermic’. Various nasty symptoms can become evident extremely quickly, including dizziness, nausea, vomiting, confusion and disorientation. During the final few moments of his 1997 Ironman, Chris Legh got within 50 yards of the finish, collapsed and, such was his level of disorientation, started crawling the wrong way along the course.

The reasons for athletes collapsing in this condition can be quite complex, but fundamentally revolve around the fact that the body, in a desperate attempt to stop more heat being produced, stops the exercise by shutting down muscles and, therefore, reduces coordination and work rate. For most people, this manifests itself in straightforward fatigue, feeling unwell and simply slowing down. But if an athlete manages to ignore the symptoms and press on because they’re ultra-motivated (say by a world title or lots of prize money
on offer), they can push it to the point of collapse. Step up here Welch, Legh, Ingraham, Newby-Fraser et al. Untreated heat stroke
can be a killer and needs to be avoided at
all costs.


As Ironman Hawaii has been held during October for over 30 years now, any suggestions about moving it to a more temperate climate or sensible time of the year are probably going to fall on deaf ears. So it comes down to individual athletes to find ways to manage their race, preparation and equipment to beat the heat. There are many ways of doing this and they fall into five broad categories…

  • Acclimation and acclimatisation training Acclimation refers to training in an artificial environment designed to mimic the heat and humidity of where you’re racing to train the body to cope with the conditions. This might be running in a hi-tech heat chamber or riding the turbo in your conservatory at home on a sunny day without a fan. Acclimatisation is where you actually travel to the environment you’re competing in and train there. Both aim to elevate the body’s core temperature for prolonged periods, stimulating adaptations such as increased sweat rate, reduced sodium loss in sweat and reduced heart rate, which are beneficial on race day. The adaptations can be measured after just a couple of days or sessions exposed to the heat and peak after around 14 days. This explains why the pros will often spend at least a fortnight in Kona prior to the race, training and living in the environment to maximise their preparation. It does indicate also that an age-group athlete training with extra clothing on or training indoors in a warm environment at home can benefit before travelling out to the race. You just have to be very careful to drink enough and not to push yourself too hard, running the risk of heat stroke in the process.
  • Body shape and size Changing your body shape and size can be very beneficial for competing in a hot environment where both heat loss and heat production can be affected. This involves the reduction of excess body fat (an insulator) and muscle (which produces heat) through training and diet. World-renowned physiologist Dr Tim Noakes from South Africa has done some clever calculations working out the theoretical running speeds possible in hot conditions for athletes of differing body mass. His figures point to the fact that in the Kona situation any athlete over about 72kg is likely to struggle to maintain the same run speed as they could in cooler conditions. Athletes under this figure are much less affected.
  • Pacing strategy There’s much discussion in the scientific community about pacing in the heat and the fact that many athletes seem to reduce their race pace – both naturally and subconsciously – when faced with extreme temperatures. The drive to do this isn’t completely understood but is a powerful factor in enabling us to complete endurance events in high temperatures. Athletes who fail to adhere to a sensible pacing strategy often succumb when it gets very hot – their rate of heat production is way above the rate of loss and the end result is walking or dropping out during the marathon. This can often happen in big races such as Kona where emotions run high and sensible thinking takes a back seat.Torbjørn Sindballe did some interesting self-analysis in Hawaii after blowing up on the run several times before 2007. He found that the difference of 30 seconds per mile (6:20 pace vs 6:50 pace) was so great that he stood no chance of finishing at the former pace (he thought he would last only four miles), but at the latter he could go the full distance. He applied his theory in 2007 having walked in previously and recorded a podium finish as a result. Having watched Chris Lieto storm past him early on in the run, he then reeled him in
    as Lieto overcooked late in the day.
  • Maintaining adequate hydration In interviews after his 1997 collapse, Chris Legh let slip that he had spent much of the race vomiting and failing to keep fluids down. This resulted in him becoming progressively dehydrated and elevated his risk of developing heat stroke. It’s highly likely that this contributed significantly to him adopting his freaky hyperthermic break-dancing routine on the home straight! In a long endurance event, it’s rare that an athlete can expect to maintain 100% hydration as losses can be 0.5 to 2.5 litres per hour and intake/absorption only 400-1,000ml per hour. But keeping up as best you can is prudent. In particular, this means both using electrolyte products that replace lost sodium rather than just water and drinking frequently during all stages of the race without overdoing it.
  • Use of equipment/technology/clothing and cooling strategies By picking the rightkit and clothing, it’s possible to increase heat loss or decrease heat gain in various ways. For the former, wearing clothing that can be kept damp next to the skin and have ice from aid stations stuffed into it is beneficial. In 2007, Sindballe even went as far as wearing a latex glove that he stuffed with ice at each stop as the palm of the hand is an amazingly effective area for cooling blood flow. He observed a significant five-eight beat reduction in heart rate with his ice glove. He also wore a long-sleeved top, wetting the forearms as they are also a good place to take heat from the circulating blood – the vessels there are numerous and close to the surface.Hats and light-coloured clothing are an obvious choice to deflect heat rays from the sun away from the body. The more pale-skinned you are, the more you should consider covering up shoulders, neck and arms with clothing or sun cream – any burns on the day of the event cause further dehydration and trauma for the body to deal with. Avoid materials that don’t breathe or have insulating properties as these will reduce the effectiveness of sweating, causing core temperatures to rise unnecessarily.


Racing Ironman Hawaii, or any other aggressively warm race, throws up a number of challenges that are less prevalent in iron-distance races held in cooler climates. To maximise your chances of performing well in the big one, the following measures are advisable: undertake a regime of acclimation or acclimatisation training in the final two weeks; make sure you’re as lean and light as possible on race day; use a conservative pacing strategy; remain as hydrated as possible before and during the event; and wear the most suitable clothing available. By taking these precautions, you minimise the chances of coming unstuck in the heat and might even enjoy skipping past a few of your competitors who are heading past ‘medium rare’ as they bake in the afternoon sun.

Photo Credit: Rich Cruse

Profile image of Matt Baird Matt Baird Editor of Cycling Plus magazine


Matt is a regular contributor to 220 Triathlon, having joined the magazine in 2008. He’s raced everything from super-sprint to Ironman, duathlons and off-road triathlons, and can regularly be seen on the roads and trails around Bristol. Matt is the author of Triathlon! from Aurum Press and is now the editor of Cycling Plus magazine.