Take your marks … the science behind the perfect swimming dive

Australia’s Cate Campbell transitioning from the on-block phase to the flight phase of a swimming start. EPA/Juanjo Martin

The swimming events of the Glasgow Commonwealth Games are among the first on the schedule. Australia and the UK tend to do quite well in the swimming events – as does Canada – so it’s an excellent opportunity to learn a little about the all-important swimming dive start while watching our swimmers compete.

The swimming dive start is highly linked to overall performance during competition. In fact, the start can contribute anywhere between 0.8-26.1% of total race time, depending on race distance.

Obviously, it’s important that elite swimmers get their dive down pat.

The swimming dive start is defined as the time from the starting signal (the gun or beep) to when the centre of the swimmer’s head reaches 15m down the pool. Elite swimmers can typically perform a start between 5.5 and 8s.

The swimming start is broken into three phases:

  1. on-block
  2. flight
  3. underwater.

The average percentage contribution for each phase of the start for elite swimmers is 11% (0.74s) spent in the on-block phase, 5% (0.30s) in the flight phase, 56% (3.69s) in the underwater phase and 28% (1.81s) free swimming.

On-block phase: The time from the start signal to when the swimmer’s toe leaves the block.

Jessicah Schipper and Stephanie Rice in the on-block phase. EPA/Kim Ludbrook

Flight phase: The time from when the swimmer’s toe leaves the block to when the swimmer enters the water.

Eamon Sullivan in a flight phase. AAP/Tertius Pickard

Underwater phase: The time from when the swimmer enters the water to when the swimmer’s head breaks the surface of the water.

James Magnussen in an underwater phase. EPA/Patrick B Kraemer

The underwater phase is the longest of a swimming start – it can account for 95% of variance in start time – and is the most decisive in determining efficient overall start performance, because it is when the swimmer is travelling at their fastest through the water.

So what makes the perfect dive?

It is important to remember the fastest starter is not always the one that enters the water first. The fastest starts are the ones that can maintain the highest velocity for the longest after they enter the water.

Prior to hitting the water, a swimmer must learn to maximise their take-off horizontal velocity while also reducing their reaction time, but if a swimmer does not optimise the underwater phase, increasing their take-off horizontal velocity won’t be advantageous to start performance.

There are a number of factors that affect the swimmer after they enter the water which determine how much velocity is maintained during the underwater phase and, in turn, the overall outcome of the start. These include:

  • being as streamlined as possible
  • starting underwater undulatory swimming (dolphin kick) after about 6m
  • generating propulsive kick using only the feet and legs during the underwater water kick phase.

The swimmer can also vary the depth at which they swim, although this will affect the amount of drag acting on the swimmer and can affect the trajectory of the underwater phase. Specifically, the timing of a swimmer’s first kick, their maximum depth and the underwater trajectory used will have the greatest influence on overall start performance.

If a swimmer’s maximum depth is too deep they will spend longer travelling up toward the surface, and if the swimmer’s maximum depth is too shallow they will experience higher drag forces acting on them.

Similarly, beginning the first kick too early will increase the amount of drag acting on the swimmer.

The ideal underwater trajectory

Elaine Tor

Through a number of research studies a number of theoretical guidelines for the ideal underwater trajectory have been detailed in the figure above, but the optimal underwater trajectory will also depend on each individual swimmers’ anthropometric characteristics and underwater kicking ability.

By using these recommendations swimmers are able to adopt the ideal underwater trajectory that will reduce the amount of resistance acting in the opposite direction to slow the swimmer down.

As a result they will be able to maintain a higher velocity for longer and set themselves up for better start performances.