the "Eco Kick" ...

[elmer fudd]

If you think a frog kick is a more efficient means to propel a diver through the water, then why don't freedivers use that kick? Certainly they need to travel the greatest distance with the least amount of energy expenditure possible.

It's all a matter of speed and water resistance. For moving at 1/3 knot with full scuba gear the frog kick is more efficient because it uses muscle groups more effectively. For moving at 1 knot in free diving gear a flutter kick is more efficient because it's better streamlined. The faster you go the less effective the frog kick becomes.

 

[DaleC]

It's more a function of fin design.

Traditional SCUBA fins are asymmetrical in design and meant to maximize thrust in one phase of the kick while reducing resistance in the other to quicken recovery time to reset the fin for the next thrust event. The design compliments frog kicking because it naturally includes a thrust/recovery tempo.

Free diving fins are more symmetrical in design (dorsal and ventral sides) and generate thrust in both phases of the kick. This rewards slow, rhythmic kicks by generating constant forward momentum. Breaking the rhythm, or even over driving it, results in a reduction of thrust (for energy expended).


Splits attempt to bridge the gap between the two designs by generating similar forces in both phases of the kick (flexion and extension). But to do without creating muscle fatigue, they bleed off resistance by splitting the contact surface which results in continuous but sub optimal thrusts.

If you want to frog kick don't buy free diving fins
If you want to free dive don't buy asymmetrical fins
If you want to maximize thrust don't buy splits