 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 progresses 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 sprints beyond this distance increasingly incorporate an element of endurance . Human physiology dictates that a runner 's near @-@ top speed cannot be maintained for more than thirty seconds or so because lactic acid builds up once leg muscles begin to suffer oxygen deprivation . Top speed can only be maintained for up to 20 metres . 
 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 <a href='uninflect' title='1'><mark>progresses</mark></a> 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 <a href='null_genetive' title='2'><mark>'s</mark></a>maximum speed . All <a href='uninflect' title='3'><mark>sprints</mark></a> beyond this distance increasingly incorporate an element of endurance . Human physiology <a href='uninflect' title='4'><mark>dictates</mark></a> that a runner <a href='null_genetive' title='5'><mark>'s</mark></a>near @-@ top speed cannot be maintained for more than thirty <a href='negative_concord' title='6'><mark>seconds</mark></a> or so because lactic acid <a href='uninflect' title='7'><mark>builds</mark></a> up once leg muscles begin to suffer oxygen deprivation . Top speed can only be maintained for up to 20 metres . 
At the professional level , sprinters begin da 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 tdasame lane on the runnin track throughout alll sprinting events , w thdaole exception of the 400 m indoors . Races up to 100 m r largely focused upon acceleration to an athlete  maximum speed . All sprint beyond dis distance increasingly incorporate an element of endurance . Human physiology dictate that a runner  near @-@ top speed cannot be maintained fa more den thirty no seconds or soo because lactic acid build up once leg muscles begin to suffer oxygen deprivation . Top speed can only b maintained ffaup to 20 metres .