Tyson, I was thinking of this thread today and I'm sure you probably already have but if not be sure to teach your son about the rest step as well as resting the weight of pack and body on the bone structure when resting on climbs instead of using muscles when at rest. It may get him further down the trail with same amount of energy expended. When grinding upwards the rest step really helps my skinny butt progress without needing to stop for a breather.

jimmyb