How much energy does a athlete need?

I usually run my 200 meters at a full sprint.

I disagree, the human body can accelerate to maximum speed over about 60 meters, after that, it is inevitable that you start decelerating. The more the brain tries to tell your body to go faster, you are pushing into a red line condition. You could hit a point of riggor mortis. So there is an element of pace and relaxation involved. You need to learn your body's capabilities. The great sprint coach Bud Winter used to teach his students to relax to let the speed come out.