Which is Harder: Marathon or Ironman Training?

A team of researchers settles the debate once and for all.

Put an Ironman competitor and a marathoner in the same room, and it will inevitably turn into a battle of the one-ups:

“I run after a 100-mile bike ride in the heat!” the Ironman triathlete boasts.

“Shuffling doesn’t count!” the marathoner retorts. “I actually run!”

And so it goes. Though there’s really no way to quantify which race is actually harder (suffering, after all, is individual), an international team of researchers has compared the training load of the two events to see if one has more impact than the other.

“It is a study based on the typical friends’ conversation comparing ‘what’s tougher?’ says lead researcher Jonathan Esteve-Llano, “Dr. Cejuela, Dr. Cardona, Dr. Moreno-Perez [other authors of the study] and I are also professional coaches. That’s why most of our research is like this, trying to solve our daily questions, searching for our needs, with the scope of improving our training programs.”

RELATED: Triathlete’s Complete Guide on How to Train For an Ironman

After identifying 15 marathoners and 15 Ironman triathletes at comparable age, weight, body type, VO2max levels, endurance experience, and performance levels (assessed by race results), the researchers put their athletes to work training for their respective events. Using an analysis of physiological data and daily training logs, the researchers calculated several ratios involving training load, training time, and competition time.

The result? The preparation for a marathon is harder. Much of this has to do with the concentration of the training—Ironman training typically has more volume, but less intensity, than a typical marathon training protocol. This may help to explain why training for a stand-alone marathon, especially one involving a PR or Boston qualification time, can leave even the steeliest Ironman triathletes feeling wrecked.

“We do not try to fade the achievement of an Ironman-distance training at all, but in terms of amount of load per time unit, it showed to be harder the average marathon training dose,” says Esteve-Llano.

Though this puts an end to the “whose training is harder” debate, we suspect there will still be much smack talk between the two crowds of endurance athletes. There is, after all, so much fodder for it: tri shorts vs split shorts, all the gadgets vs. running tech-free, and, of course, the always-heated debate about body hair.