If you don't develop your sprint stamina, you may not be able to finish alongside — or ahead of — competitors in a race. Likewise, if you play a competitive sport, you might see a competitor beat you to a loose ball or the end zone. You can, however, improve your sprint stamina, or how long you can stay at or near your top running speed. During your racing or playing season, choose interval speed training. During the off-season, go for weight training. And always stretch to improve your flexibility.