"While I suffered no ill-effects from my first few jumps (I work out constantly) my brother on the other hand comes back pretty sore every week after AFF (never works out). "
I resent that NEVER works out shit. I was in the jacuzzi for over three and a half hours doing 12 oz. curls the night prior to my last jump.
THAT, mon frere, IS a work out.
You're going to be sore. You are using muscles in new ways, under new stress and conditions.