At the professional level , sprinters begin the race by assuming a crouching position in the starting blocks before leaning forward and gradually moving into an upright position as the race progress and momentum is gained . Athletes remain in the same lane on the running track throughout all sprinting events , with the sole exception of the 400 m indoors . Races up to 100 m are largely focused upon acceleration to an athlete 's maximum speed . All sprint beyond this distance increasingly incorporate an element of endurance . Human physiology dictate that a runner 's near @-@ top speed cannot be maintained for more than thirty seconds or so because lactic acid build up once leg muscles begin to suffer oxygen deprivation . Top speed can only be maintained for up to 20 metres .