Why Crouch Behind a Metal Frame? Something to Push Against

Accelerating requires pushing backwards against something, and the force a runner can apply from a standing start is limited by friction, since a foot pushing too hard against a flat surface slips. Angled plates give the foot a surface roughly perpendicular to the direction of push, so the force is transmitted directly into a frame anchored to the track rather than relying on grip alone. That allows a far greater force in the first strides, which is where most of the difference in a short sprint is made. It also fixes the starting position precisely, so every competitor begins from the same place in a consistent posture.

Adjustment is individual and taken seriously:

• •Front block typically about two foot lengths behind the line
• •Rear block a further foot length or so behind that
• •Front plate angled shallower, rear plate steeper
• •Both distances and both angles adjusted to the individual athlete
• •The stronger leg placed forward in most arrangements
• •Settings recorded and reproduced exactly at every competition

Modern blocks contain force sensors that do considerably more than start a clock. Each plate measures the force the athlete applies against it many times a second, and the timing system records the moment at which force begins to rise above the resting level, which is taken as the moment of reaction. A reaction time below a defined threshold is treated as a false start on the reasoning that a human cannot respond to a sound faster than that, so a faster figure indicates the athlete moved in anticipation rather than in response. That threshold was set at a tenth of a second and has been the subject of sustained argument, since research finds that some athletes genuinely react faster and the figure is therefore a conservative convention rather than a physiological limit.

Analysis of sprint starts shows that the block phase determines a surprising amount of the final result. Reaction time itself accounts for very little, typically a tenth to a sixth of a second and varying between athletes by hundredths, which matters in a close race and is not where the difference is made. Block velocity, meaning how fast the athlete is moving on leaving, is far more important and depends on how much force is applied and for how long. The first strides are taken with the body inclined forward at a steep angle, gradually rising over around twenty metres, and rising too early is the commonest technical fault. Peak speed arrives around fifty to sixty metres, after which everybody decelerates and the winner is whoever decelerates least.

Before blocks, sprinters dug holes in the cinder track with a trowel to make footholds, which is why starting holes appear in photographs and accounts from the period and why runners carried trowels. The practice was slow, damaged the track and produced footholds of varying quality. Adjustable devices were developed in the late 1920s, with George Bresnahan and William Tuttle in the United States patenting an early design, and they were approved for record purposes from 1937 after a period during which performances using them were not recognised. Modern blocks are required in competition from the shortest distances up to and including four hundred metres, and are not permitted in longer events where the start is upright.

Angled plates anchored to the track give a sprinter a surface to push against directly rather than relying on friction, which allows far greater force in the first strides where a sprint is decided. Positions and angles are set individually and reproduced exactly. Force sensors define the moment of reaction, and a response faster than a tenth of a second is ruled a false start by convention rather than by proven physiology.