Are you talking about your shoulder tiring? Or is your fore-arm getting sore or something. If so, I know this helped me. I just worked out and shot my bow as much as possible. I shoot mine on 70lbs but Im so out of shape right now its rediculous. Im probably going to reduce my poundage and reset my sights or sight. I just know that I wobble after a few sets and I start pulling my shots off as of right now and I know that exercise helps me hold'er a little bit steadier.