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

Day Three
Workout: 123-mile ride followed by a 60-minute run at Ironman race pace.

Gear: Aero helmet

Hydration strategy: Alexander wasn’t given a strict drinking regimen. But Steinmetz was constantly in his ear, reminding him to drink.

Weight loss: Despite wearing the aero helmet, Alexander lost 3 pounds of body mass during the ride and an additional 0.8 pounds during the run, exactly half the amount he lost during day one with the fully vented helmet.

Temperature: Alexander’s core temperature was a constant 100.9 degrees through the first 100 miles. He lost 2.4 pounds in the next 40 minutes and by mile 117 his core temperature had risen to 101.3 degrees.

Analysis: Alexander’s temperature didn’t rise because of the helmet—it rose because he was dehydrated, and the difference in weight loss during day one and day three was his hydration.  So while the helmet might increase his sweat rate, as long as he stays on top of his hydration, Alexander should be able to race using an aero helmet without overheating.

Through all three days, Alexander’s core temperature did not begin to rise until he lost more than 2 percent of his body mass. Although an increase to 101.3 degrees wouldn’t be ruinous to his performance, the research clearly shows that dehydration alone is enough to slow him down and that his core temperature might continue to rise once he’s dehydrated in an iron-distance race. To prevent overheating and impaired aerobic performance, Alexander must keep drinking and maintain his body weight. In short, it’s dehydration—not equipment selection or ambient temperature alone—that causes Alexander’s core temperature to rise.

Steinmetz admits his testing procedure is far from perfect. “You could go through it and pick it apart. Nothing is controlled. You can’t control a five- to eight-hour training day outside of the lab. The only way to do it is to lock someone in a room and control everything.” Because temperature and weather fluctuations can have bigger effects on Alexander’s core temperature than whether or not he wears an aero helmet or how much fluid he drinks an hour, it’s impossible to know if the results of the study are accurate. Steinmetz says they did the “best we could,” but he also makes it clear that they are gathering estimations about Alexander’s physiology, not facts.

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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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