An ultramarathon seems like the logical next step for marathoners looking to push the limits and go further, but the characteristics of a good ultra-trail runner may be quite different from those of a good marathoner.
The key difference in the two types of runners is that marathoners need to be as efficient as possible, burning as little energy as they can at a given pace so that they can make it to the finish line without running out of fuel. In ultras, on the other hand, being efficient is less important than being able to handle the muscle damage that accumulates over the course of the race. It’s no help being a bit more efficient if your legs are so shot that you can’t keep running.
So is it possible to be both a successful marathoner and ultra-trail runner?