Jumping rope is also a good warm up exercise, as well as jumping jacks. Now I wouldn't say not to stretch before a workout. I would say limit your stretching before the workout. You should stretch before the workout, but just a little. Just to activate the ligaments/tendons. I always like to do like 5 dips and 10 push-ups before I work Push and 5 pull-ups before working Pull. But most if the stretching should be done after the workout and without force/strain on the tendons so you don't hurt/injure them. But I would recommend stretching just a bit before the workout to get the muscles and ligaments ACTIVATED. I stretch my wrists before doing muscle ups or handstand push-ups. Because of the motion/force/flexibility that I'm asking them to give me, I can't just start right away. They need to get warmed up as well. Same goes with almost(I would say all) muscles and ligaments/tendons that you work out. So I would say stretch before workout but don't over do it or you might get injured like Martin said. The warm up is super important as well, get that blood pumping and your muscles/tendons warmed up as well. Be careful though, remember, safety first. Hope I helped!