it also depends on the muscle structure you have built up. sprinters usually have fast-twitched fibers in their muscles that contract faster but also fatigue faster, whereas those that can go long-distances by jogging at a slower pace have slow-twitched fibers that use oxygen during movement and fatigue less easily but produce less contractions. so those that are new to running cant start off by sprinting fast because theyre muscles will tire more faster, may causing injury to them. they have to start off slow to build up those fibers, making thier muscles stronger and then gradually move up to sprinting, if they want. but most people will go back and forth between the two, as in starting off slow, then speeding up, then slowing down again.....theres also somethign about how the type of fibers you have in your muscles depends on genetics also.
(yes, sally, ive actually been reading that physio psych book)
ehn, im not a sprinter. lol. im an endurance runner too.