The RX jump rope is my best friend. I used to be so bad at double unders and one of my main fitness goals was just to be able to do them well. This is the rope I used to achieve that goal and get a great cardio workout without the treadmill.
Jump roping is fast, quick, and doesn’t take up any room. The "whip factor" on this rope is no joke, if you are doing double unders the whip will remind you to pick up the pace. This can be used it for a warm up and then go into dynamic stretching. I'll do 20 double unders and then go into strength and alternate, or 100 jumps and then 15 bench presses and do a circuit. It's a nice way to get your heart rate up...and if you can remember your childhood, you can do it!