Hi, I have been reading some research online which seems to all conclusively say that the energy a person expends during a workout is indpendent of their running speed (http://www.runnersworld.com/weight-loss/mythbusting-running-mile-always-burns-same-calories). It only depends on things like your weight, fitness levels etc. So if two people the same weight, height and fitness ran 5 miles then it wouldn't matter who ran it the fastest - they would both expend the same energy. I was just wondering if this fact comes from any fundamental laws of physics? Would there be any equations that could prove that a quicker running speed over a shorter distance is the same as a slower running speed over a longer distance?