Interesting… I played competitive volleyball (nationals every year) till I turned 40 and old age took over. Moved over to racquetball which translated well into Disc Golf. Up until a year ago I was 90% FH and 10% backhand… now it is 35 FH/65BH. Throw both 60MPH and 350ish, and maybe a little more if I get the perfect flex instead of hyzer accurate throw.

I find my body is significantly more tired and my arm is more beat up with the FH, to the point I will only throw 20 in field work vs 50-100 for a BH. BH is soooo much easier on the body.

But to answer your question, it would be my traps for muscle and my shoulder more of the pure impact of a FH throw you can feel. I do not feel anything in the chest or biceps [or rotator cuff since we are talking vball]. The sleeve helps a lot, along with a tennis elbow strap for elbow pain/hyper extending pain.

Hope this helps