From The Inside Triathlon Archives: Getting To The Core

  • By Aaron Hersh
  • Published Feb 10, 2012
  • Updated Oct 31, 2014 at 4:37 PM UTC
Photo: John Segesta

The Conditions
Contrary to what some might believe, it’s the island’s humidity, and not its ambient temperature, that is so deadly to racers. The average high temperature on race day is 84 degrees F, which makes Kona only the fourth hottest Ironman in the world. The temperatures aren’t exactly mild, but they aren’t as high as the race’s reputation might lead you to believe.

The humidity is a killer because the body relies on sweat to cool itself—but simply wetting the skin doesn’t dissipate much heat. Sweat has to evaporate to cool the body, and the rate of evaporation is determined by the humidity in the air. Kona’s moist climate prevents sweat from cooling the body because it prevents sweat from evaporating. Instead, it simply rolls off the skin. In a vicious cycle, the body just keeps dumping more and more sweat onto the skin, and in turn the body becomes hotter and more dehydrated. This downward spiral often ends in a poor performance and even the occasional catastrophic collapse, which NBC highlights annually to show just how demanding the Hawaii Ironman actually is.

In the past, Alexander has famously raced in a fully vented helmet in an effort to keep the onslaught of dehydration at bay, but switching to an aero helmet could save him upwards of 10 watts. That may not be a life-changing improvement for an age-grouper, but it is roughly equivalent to the fitness gains Alexander has seen over the last two years.

Alexander based his decision to race in a fully vented helmet on personal perception—not hard data that specifically shows him what causes him to overheat. With the aid of an unlikely ally—someone Alexander stumbled upon by chance—Alexander is now studying what actually causes him to overheat and whether or not he needed the fully vented helmet in the first place.

Mat Steinmetz was a 20-something triathlete struggling to pay his bills when he joined Retül as a bike fitter in the fall of 2009. Shortly after, he began helping Alexander, and Alexander immediately felt more comfortable in the saddle. Slowly, Alexander came to trust Steinmetz, and less than a year after the meeting, Steinmetz became one of Alexander’s most trusted consultants.

Beneath Steinmetz’s humble background is a master’s degree in exercise physiology and years of experience in endurance performance labs. Steinmetz recently found several studies that could be the key to Alexander’s title defense in Kona. They are summarized in a review published by U.S. Army scientists in the Journal of Applied Physiology. The review says that “when dehydration exceeds 3 percent of total body water (2 percent of body mass) aerobic performance is consistently impaired.” In other words, the review explains why dehydration—not just core temperature—is the key to Alexander’s performance at this year’s world championship.

During a six-day training camp in July 2010 in Kailua-Kona, Hawaii, Steinmetz and Alexander used this review as the foundation to test out various hydration strategies—all with the aid of a tool that perhaps is even more unlikely than Steinmetz himself. Inside Triathlon was on site for three of the six days.

TriCenter From Kona: Managing The Heat

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Aaron Hersh

Aaron Hersh

Aaron Hersh is the Senior Tech Editor of Triathlete magazine. To submit a question, write Aaron at

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