I really don't know, if it's advisably to make some kind of body buildung to improve trials skills. Nevertheless I did it for a while. Unfortunately I neglected riding trials at this time, according to this my hops werent going any higher. Later on, I decided to abandon weight lifting and to ride trials more often. My bunnyhop height increased from 1,05 metres to 1,25 in this time. Now I've reached a point where it seems to be pretty hard to become better. Perhaps this would be the right time to go on with weight lifting. But as I know, I would be riding my bike less often, and that would be bad for my skills, too. So I keep practicing without weightlifting. Sometimes I'm jumping stairs up to the 10th floor, by making some kind of "box jumps" (you know what I mean). But it seems to be senseless. So what I can promise you: To get a clean technique, the less power you have, the better it is! If you're already a muscleman, you will gain height by using your power, not your technique. So if you're jump less than one meter, please don't workout!!!! Best moment to begin working out, maybe when you're stagnating. But also be patient. I often made the experience, that I wasnt getting better for a few month and then BAM! immediately I was able to jump onto higher ledges than before. If you really what to do weightlifting, do squats, pullups or back lifts. Perhaps some shoulder workout, too. Everything with max. 5-7 repetitions per set (this is the best workout for explosive power). But that should be enough! Keep muscle training small.