In addition, to what he eats during the ride, one of the most important things is that he eats immediately after the ride. He needs better recovery. He may try a recovery drink right after the ride as well and this may help. It may also be because he is training a lot during the week and he just may be training too hard without enough off-time recovery time.

Do you train as much as he does during the week; maybe this is the difference between your strength on the weekends after the ride and his lack of?

There are a lot of variables that may be contributing to him being that tired.