A sprinter appears to accelerate through the finish, but the fastest part of the race happens earlier. What is being watched at the end is a difference in decline.
Top speed arrives before the finish
Acceleration continues for the first portion of a sprint and then flattens. Maximum velocity is typically reached somewhere in the middle of the distance rather than at the end.
After that point every runner slows. The sprint becomes a question of how gradually that decline occurs rather than whether it occurs at all.
A runner who appears to surge past rivals in the closing metres is usually decelerating more slowly than they are, not accelerating. The gap closes because the field is slowing at different rates.
The energy system runs out
Maximal sprinting is fuelled by stored compounds within the muscle that are available immediately and in very limited quantity.
Those stores deplete within seconds, and the systems that replace them cannot supply energy at anything approaching the rate maximal sprinting demands.
Deceleration is therefore not a failure of technique or willpower. It is the direct consequence of a supply that runs down faster than it can be replenished.
Stride mechanics change as fatigue arrives
Speed is the product of stride length and stride frequency. As fatigue develops, frequency usually falls first while the athlete attempts to maintain length.
Ground contact time lengthens, which reduces the proportion of each stride spent airborne and lowers the force applied per step.
Technique breaks down visibly in the final metres, with rising shoulders and a shortened arm action, all of which are signs of the same underlying decline.
The start matters more than it appears
Because the closing phase cannot be improved much, races are frequently decided by the acceleration phase, where the differences between athletes are largest.
Block clearance, the angle of the first strides and the transition to upright running all determine how quickly maximum velocity is reached.
An athlete who reaches top speed earlier spends longer in the decline, however, which is why the fastest starters are not always the fastest finishers.
Longer sprints invert the balance
Over two hundred metres and beyond, the deceleration phase occupies a much larger share of the race, so the ability to resist slowing becomes decisive.
Training for those distances emphasises tolerance to the by-products of anaerobic work, which is a different physiological target from pure acceleration.
This is why athletes who dominate the shortest sprint do not always transfer successfully to the longer one, despite the events appearing closely related.
