I have tried playing the backhand with one or two hands, to see which one fits me. The onehander feels better to me, more natural and fluid, plus my slice is getting better. However, after 40 minutes or so of play, my right arm is dead from hitting all shots, and my technique goes out the window. Which results in a lot of missed shots. So I shift to a twohander, and immediately start to apply pressure with my backhand again. What kind of offcourt workout should I do to get in better shape for hitting the onehander all the time?