Are your legs long or short compared to your torso? If they are long: you can run well, have a low center of gravity, always land on your feet, are a good candidate to be a good athlete...
However, if they are short compared to your torso: You run slow no matter how well you are conditioned, you are top heavy, tend to land on your head when you try to be a gymnast, not a good candidate for competitive athletics.
A University of Houston physical education teacher explained that to me when I asked him that very question...