id probably do sit ups and push ups. but even with those i use a lil weight. or you could try these squating things we did for hockey. you dont use weights. just cross your arms across your chest and squat up and down as many times as you can and do them fairly quick. it seemed to give a good burn in my legs. but i dont know if it really has much potentential to building muscle. it was pretty much just a warm up for practice we were doing. also check out the fitness tech section of the forum i think i saw a weight less excercise article in there maybe.