The Case for Middle Distance Running

Many people have written about the physiques of sprinters versus marathoners.  Sprinters are generally muscular and lean, while marathoners are more frail though still lean.  Given the two, I'm sure most people would pick the physique of a sprinter.

However, these two cases represent the extremes.  Perhaps athletes that run distances in between a sprint and a marathon are in better shape than either of the two extremes.

I found this paper that shows that in masters athletes, middle/long distance runners are leaner than sprinters.  This held true for both men and women.  For men, the runners averaged 10.5% body fat, while the sprinters averaged 13.1%.  For women, the runners averaged 18.5% body fat, while the sprinters averaged 22.2%.

It seems likely that there is a "sweet spot", as far as the main competitive distance, that could maximize body composition.  I think 100m is probably too short.  It doesn't activate the aerobic system enough and hence, misses out on some fat-burning benefits. 

Distances like the half-marathon and up are probably too long.  That much running tends to diminish muscle mass and also may not provide enough overall intensity.

It's speculation on my part, but I would think that a primary distance between 400m and a mile might optimize body composition.