Does he like swimming? I'd work on strengthening any points of weakness in his body.
Why don't you try a natruopath of TCM practitioner? Traditional Chinese Medicine is awesome for pinpointing areas of weakness in the body as a whole and treating as such.

I think Justin at the BB centre would be worth seeing, if my DS continues the same way as yours, that's what I'll be doing.

He is a little chatterbox isn't he? His lungs are probably overworked