There are several variables in the block phase, the most important being a good stable setup on the block to allow for the most powerful take-off.
In any timed event the start is a critical component to the perfect race. This is especially true if we consider the start in any sprint event. A slow, or otherwise poor start can cost the win for an athlete. While in sports such as track and field a slow start doesn’t necessarily affect how you recover as you continue to race, in swimming there is a dramatic change in element from air to water, and in a sprint event the start can make or break the outcome of the race.
It was estimated by Cossor and Mason that at the 2000 Sydney Olympic Games start times comprised 0.8% to 26.1% of the overall race time. This means that on average, for swimmers covering the 50m freestyle, the start accounted for a quarter of their race.