Developing strong fly kicking skills on your back underwater is vital for performance. 

Fins  play a major role in developing the butterfly kick underwater as the swimmers must be propulsive and able to maintain constant depth at speed.  It is difficult for young inexperienced swimmers to maintain effective propulsion and depth without fins.

Nose clips assist by allowing the swimmer to concentrate on body position and propulsion without the discomfort of taking on ballast through the nose.

As the swimmers become more proficient more and more kicking should be done without the use of a nose clip along with varied use of the fins.  Sometimes with fins and sometimes without.

The mechanics of the kicking action should be mastered first but in tandem with the ability to remain at a constant depth underwater for at least 10m on a single breath. After mastering these two facets we then go for the development of speed. If you can’t kick faster than you can swim then it is no advantage to you.

Short sprint sets of this type of kick every session will help master these skills.  It is valuable during these sets to get the swimmers to kick at varying depths using gradual paths of ascent to the surface.

The rules allow us to travel 15m underwater off the start and every turn. In long course swimming this means 30m / 100 and 60m / 200.

In short course swimming it is 60m / 100 and 120m / 200. This means that if you want to take full advantage of a great underwater kicking ability you not only have to be trained to kick fast but you have to be trained to stay under water for extended periods under stress which has both physiological and psychological components.