short tight muscles?

exercising does not shorten the bones, thats the only way to physically shorten a muscle, reduce the length it has to span.
Lean means to have little fat on, they guy has no problems in this area

I am 190lbs and people from my Taekwondo club will hardly describe me as slow

I haven't changed the guys training routine as he is geared to boxing but weights are an essential tool in all sport training.