Beat The Heat – Elite Marathoners Tactics
Article by Renata Bossi of Sweat Elite
Elite marathon runners are by no means unaccustomed to scorching temperatures, and the enervating effect of both extreme heat and humidity on performance. It only takes a brief glance at their competitive calendar to understand why, yet it demands delving below the surface of physiology and heat acclimation to understand how they outrun the searing sun.
The 2020 Summer Olympics set to take place in sauna-sweltering Tokyo, which has since been postponed to 2021, was predicted to be the hottest on record. So hot in fact, that the 26.2 mile marathon course was resurfaced with a heat-reflecting material called ‘Perfect Cool’. While reducing the surface temperature of the track by up to 10 degrees Celsius on hot days, further analysis found there to be hardly any cooling effect at head height, deeming their heat expelling attempt to be rather futile.
Marathoners competing in the 2019 IAAF World Athletics Championships in Doha, Qatar, raced at midnight to avoid the brutal daytime temperatures. Albeit efforts to avoid the heat, thermometers still recorded a blazing 32 degrees Celsius with 70% humidity at 00:00. More than 40% of the field, a whopping 28 of the 68 starters, dropped out.
Beholden to the vagaries of broadcasting agencies prioritizing more lucrative sporting events, running events are rarely scheduled when environmental conditions are optimal. Many competing athletes questioned why white-hot Doha was awarded the championships for 2019, and criticized the resultant poor spectator attendance.
With regards to the poor timing of the 2020 Summer Olympics, Dick Pound, a member of the International Olympic Committee (IOC) and former chairman of its television negotiations committee, stated that “It’s essentially driven by American television.” Nearly 75% of the IOC’s revenue comes from broadcasting rights, and almost 50% of these rights are paid by the American broadcasting company, NBC. The scheduling of the Olympics, therefore, has to scrupulously slot into an already action-packed sports broadcasting schedule, with July and August being the ‘quieter’ months. Perhaps this is why heat acclimatization has become so necessary, as many athletes are running races in environmental conditions far from conducive to peak performance. They are forced to adapt, and somehow continue to break records, notwithstanding substandard circumstances.
Despite the fact that the 2018 London marathon went on record as the hottest London marathon to date, Eluid Kipchoge excelled and won in a time of 2:04:17. But the urge to ‘beat the heat’ does not stop at the marathon mark. Regarded as ‘the toughest foot race on Earth’, the multi day self-supported Marathon de Sables traverses 251km of the Sahara Desert, with midday temperatures surpassing the sweltering 50 degree Celsius mark. By no means the most enticing race conditions. While many are unsuccessful at mastering the body’s reaction to heat, year after year, elites still excel at these formidable events.
A study done by Matthew Ely et al. (2007) looking at the impact of weather on marathon running performance, found that there was a progressive slowing of marathon times as the wet-bulb globe temperature (WBGT) increases from 5 to 25 degrees Celsius. Results from seven mass participant marathons, including Boston and New Year Marathon, found that this decline in performance held true for both men and women. Furthermore, slower runners were more severely affected by an increasing WBGT.
While the marathon times of elite runners increased by 1-2 minutes (up to 1.5%) when racing at temperatures of 10-15 degrees Celsius, advanced marathon runners saw a more severe 4-8 minute (up to 4.2%) increase in completion time when racing in the same temperature bracket, with completion time continuing to rise as the temperature increased.
Nomogram examining the potential performance decrement (y-axis) based on projected marathon finishing time (x-axis) with increasing WBGT.
Not only is this important in confirming the hypothesis that environmental conditions greatly impact performance, but it also highlights that the ramification that an increase in temperature is more sorely felt by ‘slower’ runners. Elite runners are better equipped to deal with the heat. But what makes their physiology more adept at performing in warmer conditions?
In a study conducted by Marino et al. (2000), researchers looked at the advantages of having a smaller body mass during distance running in warm, humid environments. The following results were established after testing sixteen accomplished runners of varying body weight (55-90 kilograms) on motorised treadmills at 15, 25 and 35 degree Celsius heat, with a 60% relative humidity. Runners with a lower body mass both produced and stored heat more slowly than runners with a higher body mass. This is important for excelling in hot conditions as it delays the time that it will take the core to reach a critically high temperature that eventually leads to a decrease in performance. The results also showed that a decrease in body mass reduced oxygen consumption, reducing the rate of metabolic heat production. The study concluded that “compared to heavier runners, those with a lower body mass have a distinct thermal advantage when running in conditions in which heat-dissipation mechanisms are at their limit. Lighter runners produce and store less heat at the same running speed; hence they can run faster or further.”
What exactly happens to the body when temperatures rise?
The body reacts to heat by increasing the volume of sweat produced, as well as increasing blood flow to the skin which helps reduce its internal temperature. Sweat evaporation enables heat dissipation, with 580 kcal of heat energy extracted per 1 litre of sweat evaporated. However, high humidity reduces the rate of evaporation, which means the body incurs a fluid deficit via sweating, without the much needed loss of heat through evaporation.
As a runner’s core temperature rises and blood rushes to the surface to cool the skin, there is less blood flow available for muscles to use. The body compensates by increasing heart rate and decreasing blood flow to organs that aren’t in direct use. Eventually the individual’s core temperature reaches a threshold, and fatigue and a decline in performance sets in. However, this maximum core temperature is variable. “The level of core temperature which becomes limiting for exercise performance may depend on many factors (e.g. duration and intensity of the exercise, dehydration, nutrition, fitness and motivation), and therefore in absolute terms would be expected to vary markedly,” noted B. Nielsen et al.(1993) in a study looking at human circulatory and thermoregulatory adaptations with heat acclimatization.
To improve race results in both hot, and consequently cold conditions, runners need to train in environmental conditions similar to that of race day. Heat acclimation or acclimatization occurs when the body is repeatedly exposed to heat, and results in noteworthy improvements including increasing exercise time to fatigue. Furthermore, it results in a lower rate of rise in both heart rate (HR) and core temperature, as well as an increase in cardiac output (the amount of blood the heart pumps through the circulatory system in a minute) and sweat rate. The extent of adaptation will depend on intensity, duration and the frequency of heat exposure, as well as innate physiological aspects unique to each athlete.
For optimal heat acclimatization, athletes need to spend at least 7-14 days exercising for between 90-120 minutes, in a hot environment. The intensity and duration of exercise should gradually increase between day 1 and day 14. Each day, the physiological strain induced by exercise heat stress will begin to abate. Studies done by Sawka et al. (1996) and Pandolf (1998), indicate that most of the physiological improvements occur within the first 7 days, with the reduction in heart rate occurring the most rapidly in 4-5 days. Thermoregulation related adaptations are completed by day 10-14. It is worth noting that aerobically fit athletes can attain heat acclimatization up to 50% faster, and keep the adaptations for longer than those unaccustomed to aerobic exercise.
Improved cardiovascular stability, superior fluid-electrolyte balance, improved sweating and blood flow to skin are all favourable results of heat acclimatization. Not only does sweating start earlier, but sweat glands become better adapted to endure fatigue, enabling the higher sweat rate to continue for a greater duration. The positive consequence: skin temperature and body heat storage decrease as the improvement in sweat rate enables greater evaporation. In conjunction, the athlete will experience an improvement in heat-related performance.
To maintain these adaptations, heat training must occur every 2 to 3 days. Unfortunately, heat acclimatization disappears almost as rapidly as these adaptations appear. While the benefits remain for about a week, by the third week post-acclimatization, about 75% of the adaptations have disappeared. However, re-acclimatization during this period occurs more rapidly than at first.
Although most running races have been cancelled on a global scale for the remainder of 2020, one can only wonder what the summer competitive calendar will look like in 2021. Will the currently vacant broadcasting schedule mitigate poor race placing, or will big corporations continue to monetize sports broadcasting in spite of the ramifications on athletic performance? While environmental conditions may be out of a runner’s control, heat acclimatization is a training technique that reaps a plethora of performance-advancing physiological adaptations, that will benefit runners of all capabilities, when carried out correctly.
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