some crazy runner guy wrote:
I know a lot of responses on here have advocated weight lifting. I highly discourage weights. They will make you slower and heavier. Remember that any weight you gain you have to carry with you every step around the track. Try putting on a ten pound weight belt and trying to run a PR on the track, I bet you won't be able to. Yes there are freaks out there like Sol but really the best distance runners in the world are right around your weight. If I were you I would just do the right type of running and let my body figure what shape it should be.
Your comparison to grabbing a 10 pound weight and running arround a track to gaining 10 pounds of muscle does not make sense. Ten pounds of extra weight that does nothing is not the same as 10 pounds of muscle.
And for middle distance, I would not say most top athletes are 113. Yes,many top mid-d runners who are east african are 120-130, but depending on this kids body type, he might run better with more muscle. I used to be 126 at 6 feet and ran decent. Senior year, I gained a ton and went to 160, all my times from 800 to 2 mile dropped and I finally had a kick.