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Jumping is one of the best and most demanding calisthenic/cardio-endurance exercises. It is harmless to knees and hips because it is on toes.
Like most things, it takes practice to get to the point where it is useful. I am working towards a repertoire of jumps, but it is more difficult than it looks and I am not highly-coordinated. (If you think you are, try double unders sometime and let me know.) Also, I find just two minutes of speed rope to be quite fatiguing. That's why I embed a minute or two of rope in a circuit of calisthenics. Cardio and calisthenics are a waste of time without intensity.
This guy is an expert. It's like watching a dancer. His double unders are great. Three things to watch: 1. His body stays in a relaxed athletic posture with no tension 2) The rope usually maintains a steady pace regardless of what his legs and feet are doing (he is mostly not doing speed), and 3) His hands and arms remain in the same position.
I wish it WERE harmless to knees, but it exacerbates my former dancer's/marathoner's knee pain. Of course that could be because former dancers have bad toe joints...
Also, I should add that of all the exercises you can do, jumping is absolutely, positively the worst for your spine and joints. No matter how skinny you are or how catlike your landing on toes...Not that it isn't fun, beautiful to watch (in ballet) or just a good way to burn up calories in dreary calisthenics. If you MUST jump, jump on a springy wood hymn floor or on springy turf. Something with give. Never on hard, unyielding surfaces that will jar your spine or joints...