Build their muscles from something other than carbon proteins such electroactive polymers. There are several options for alternative muscles besides polymers.
Reducing the weight of the skeleton won't get you much as skeletons don't make up much of the weight of an adult human. Increasing the diameter of muscles doesn't scale very well as the ratio of muscle strength to diameter follows the cube-square law. This limitation can be avoided by making the muscles out of something else with a greater power capacity than normal human muscle.
Evolutionary of Electroactive polymer Muscles
Since movement is such a basic component of life, electroactive polymer (EAP) muscles would need to be realized in a situation where EAP muscles develop before normal protein muscles do. The earth equivalent to when these EAP muscles appear would be around the time of the Cambrian Explosion because if protein muscles show up first, every creature that comes afterwards will have protein muscles as we see here on earth.
The tradeoff between EAP and protein is that protein muscles use predominantly chemical energy in the form of carbs to work (fats work too) while EAPs are purely electrical. Energy storage in terms of batteries or capacitors accessible to the muscle will need to arise and stay charged. I'm sure that Mother Nature could come up with some fabulous dielectric materials for the capacitors.
We know that electricity can be stored and discharged by animals because the electric eel exists. The best way to capture electric eels is to get them to discharge till they're exhausted then wade in and grab them.
So, in addition to being able to jump higher, they'll be able to do about twice what normal humans can do. Run twice as fast, rock climb better.