In the first half of the chapter on environmental factors which affect training and performance, we focused on the impact of altitude. In this final section of the chapter, we will turn our attention to another environmental factor that can have a large impact on performance – heat.
Many endurance sports find their top competitions taking place in the middle of the Summer and that frequently means that heat can have a major impact on performance. This is especially true of some particular sports/events. For example, the Tour De France, taking place in July each year is well known for encountering some sweltering days, especially as the riders get deeper into the race and approach the the lower latitudes in the South of France. Given that this is a three week event, the cumulative effect of any dehydration that the riders might accrue on those days can be decisive in the important final stages of the race.
Even more severe conditions can be found in the Ironman World Championship – an event that traditionally takes place among the barren lava fields of the Big Island of Hawai’i. Typical temperatures of the race are in the range of 80-90 degrees Fahrenheit, but when combined with the high humidity of the island, the environment plays a massive role in the performance that the athlete is able to accomplish on the day.
Finally, at the even greater extremes of environmental challenge, come races like the Badwater Ultramarathon. This 135 mile/217 km running race begins in the Badwater Basin in Death Valley, the hottest place in the U.S. – where temperatures can reach 130 Fahrenheit (54 Celsius) in the middle of the day!
Less obviously, shorter races in relatively warm temperatures can be equally challenging. As we will see shortly, heat accumulation is a function of both heat dissipation and heat production and, at the higher intensities created by shorter events, heat production is significantly higher, leading to challenges at what might even be considered relatively mild temperatures for longer events. For example, in the 2016 ITU WTS Grand Finale in Cozumel, Mexico, despite “only” a ~1hr 30 minute race duration, the U.K.’s Jonny Brownlee, on the verge of winning the championship, found himself showing quite severe heat exhaustion in the final stages of the race – appearing disoriented and on the verge of collapse. Fortunately, his brother, Alistair was right behind him and was able to assist him across the line to help, in what has become a truly iconic moment of sportsmanship and brotherly bonding.
Jonny Brownlee sweating it out on the run with brother Alistair never far behind…
Mike Egerton | PA Images / Alamy
But before we get too carried away with the sappy stuff, let’s take a look at the general physiology of heat management. How do we (humans) do such a remarkable job of dissipating high levels of generated heat?
The first, and most important thing to understand is that most of our methods of human locomotion are not especially efficient. For example, on a bicycle, of all of the internal metabolic work created, only 21-22% of it makes its way to the pedals, the rest, a whopping 80% is lost as heat. In other words, if a cyclist is seeing 200 watts of power reaching the pedals or cranks, in actuality, they are generating close to 1000W of power at the level of converting food into energy at the cell, i.e. 800 watts of all the power generated is lost as heat. And, it must be lost…
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