The poster below forgot that the 2x sized sprinter would also be fighting 8x the inertia in his legs as he reaccelerated his legs forward and backwards. Also, this theoretical person would not be 8x as powerful. Strength is related to muscle cross sectional area, not length, so they would only be 4x as strong. However, their legs would move over roughly the square root of 2 times the 1x sized person. This means their work would be about 4*root2, or 5.65. Even if their turnover was the same (but it wouldn't be of course), their power could be approximated at 5.65x. In sprinting, power is roughly proportional to top end speed.So why isn't the shortest sprinter the fastest? Because as you shorten your stride length, you have to increase turnover to go the same speed now. Now you have that v^2 component that you are fighting. There will be some point in the middle where humans are the fastest. As your ability to produce power quickly increases (you have more fast twitch %, higher muscle recruitment, faster CNS etc), the closer to the tall end of the spectrum this will shift, because now you have the power to overcome the disadvantages of longer, heavier legs.Bolt has no choice but to take slower strides. His only hope to be competitive is to keep his longer legs from being a disadvantage. Clearly he and his coaching know this, which is why you see his form look the way it is. Look how short he makes his levers on the return to minimize energy required. Look how high his knee drive is to be able to use his glutes/hamstrings/quad to power his leg back down. If he didn't take the time to let his leg move through these positions, he would be significantly slower. Keep in mind this is well studied in other fields, such as entomology. IE, there are no longer 8 foot wide dragonflies. Why? Because our oxygen saturation levels are lower, so they aren't capable of carrying oxygen to the exponentially larger muscles required in our current environment, so they evolved back down to a smaller size. With insects, it is more extreme of a change because of their exoskeleton, but that is a different discussion...So why is Bolt faster? Well, you could believe drugs helping to increase power, you could believe that it is his differences in form allowing him to remove to maximize his power, you could believe he is a freak of nature (higher muscle recruitment, more fast twitch, faster cns, etc), or you could believe some combination of those things. The fact is that he is faster and without more facts (knowledge for sure if he is doping, muscle sample, "watching" his nerves fire...), we can't get at the real answer.