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taller athletes or longer limbed athletes have an advantage when it comes to certain movements. I learned in my advanced biomechanics class thats it mostly about the different levers in the body. Taller people have a harder time putting on muscle but their levers allow them to display power more efficiently. Without going into too much detail, in general longer levers require less force to move a given resistance. This is one of the reason why an athlete who is 6'4" can squat 1.5x his body weight or less and jump 40+ inches and shorter athlete let say 5'9" would sometimes have to squat in excess of 2.0x his body weight to get that same 40+ inch vertical. Thats why some guys are just natural jumpers due to limb length, they require less strength. Just look at the longer limbed or taller athletes on tv, they look and move like they are not trying because they really aren't. Then take a look at the shorter more muscular athlete and he might be moving the same speed but he struggling to do it. Both pitchers and hockey players with fast puck and ball speed are more than likely taller athletes due to arm length. Usain bolt isnt doing any special training, he is just that much taller than average world class sprinter. Sports training industry used to have a nack for measuring an athletes potential by weight room numbers, but taller and lanky athletes excel more on the field.

There are many more variables that go into jumping but thats one of them.
To sum things up: lever or leg length > brute strength