For argument’s sake, let’s say you’re eating too much cake, and your training volume isn’t high enough to float you across an Ironman finish line in a podium-worthy time. We don’t know why you’re slow. But Swiss researchers just published a study that might give you some clues.
Published in the journal Medicine and Science in Sports and Exercise, the study followed 38 amateur Ironmen (34 of whom were male) as they trained for and competed in Ironman Zurich in 2010. The athletes kept detailed training journals during the three months leading up to the race. Then, the day before the race, they all received echocardiograph exams (a sonogram—the technology used to see babies in the womb—of the heart). Finally, researchers related that training and physical data to the athletes’ finishing times.
What they found: the strongest predictor of finishing time is right ventricular end diastolic area, or the area of your heart’s right ventricle (the chamber that pumps blood into your lungs) when it’s full of blood. Endurance training, it’s been shown in several studies, can lead to an increase in right-ventricular end diastolic volume. Genetics also plays a role, as does gender: males tend to have significantly larger right heart measurements than women.
But only expensive tests can tell if your right ventricle deserves blame for your underperformance. Lucky for you, the Swiss researchers identified one other easily measured variable that significantly correlates to total race time: percent body fat. This shouldn’t come as a surprise; other studies have concluded that in men, percent body fat has a lot to do with how fast you’ll finish an Ironman—mostly because skinny dudes run faster than heavier guys. (Note: For women, several studies have found that training volume has more impact on race time than percent body fat—the more women train, the faster they go.)
THE BOTTOM LINE: Maybe you are eating too much cake and not training enough. If you’re hell bent on medaling, pay attention to your body fat. Active.com states that Ironman champ Chris Lieto races at about 5.5 percent body fat, while the average non-pro Ironman starter involved in the study that found skinny guys that finish first had 15.1 percent body fat.