I think the mental fatigue and travel probably wear on these kids, but I don't buy the tired legs.
Most of us probably played sports when we were younger. I was not the best athlete in the world, but I played basketball until I was 17 and competitive soccer thru my sophomore year of college. We would play in countless weekend tournaments where we might play 4-5 games in a day, sometimes two days in a row if we made it to the finals. Yes they were condensed games usually (55 minute soccer games instead of 90), and in NO WAY am I comparing the level of competition and play to what Duke men's basketball plays, but I don't remember being all that tired after 5 hours of soccer or basketball in a day. Plus these kids have the best conditioning coaches in the business.
Just my $.02