My thought are this.... if the person is a good woodsman, who can safely quickly & confidently move through a variety of terrain & conditions, then their size is less on an issue.

I am a big guy & have never had issues traversing through terrain efficiently.... I learned a long time ago how to move through the woods. Keep your center of gravity at your core, take smaller confident steps, go around what you can & always step over an obstacle, not onto it.

With that said, I believe athletic type people like in any other sport are in the best body condition.... regardless of size.

Troy