Fin Propulsion and Force Fin’s Efficient Kick

Populsive Divers Kick, Efficient Kick

Divers propel themselves by moving their legs (and the increased surface area of their fins) back and forth against the water with a flutter kick motion. This kicking results in a complex combination of propulsive forces that move the diver forward as well as resistance or drag forces that hinder that movement.

With other fins, virtually all of the propulsion comes from the downward phase of the kick (imagine you’re horizontal in the water with your stomach toward the bottom) and almost none on the up-kick. You can test this yourself in the water by trying to kick up, with or without fins. You’ll go nowhere. But simply extend the lower leg down and watch yourself move ahead.

Force Fin KickOne reason for this uneven propulsion is that humans naturally have more strength when kicking down. The power or downward phase of the kick emphasizes the powerful quadriceps muscle group at the front and side of the upper leg. The kick’s upward phase uses the weaker hamstrings at the back of the thigh and is mainly a recovery movement setting up the leg for the next power phase. The result is a natural two-stroke kicking cycle of power and recovery for each leg. It’s the same with other continuous activities like running, bicycling or swimming where a power/recovery cycle is built-in to conserve your energy.

While most other fins make you work just as hard on the recovery as on the power phase, Force Fins take advantage of this two-stroke cycle and work in harmony with the body’s natural strength. The flexible blade of our Force Fin opens out to its maximum surface area to move a high volume of water during the powerful downward portion of the kick.

During the recovery, the blade folds down, channeling water behind while limiting resistance to conserve your energy. (If you have to put the same amount of energy into both parts of the kick, you fatigue much sooner.)

As you kick down, the blade opens out to its maximum surface area, engaging the muscles of the whole leg to push water and provide initial forward thrust.


At the end of the downstroke, the fin recoils, setting up to rebound to its original position during the recovery or return kick stroke.


The fin then rebounds to help begin the upward recovery phase of the two-cycle kick stroke.


The fin’s tips fold inward to aid the upward recovery and to prepare your leg for the next downward power stroke.


Force Fins are the only fins that provide propulsion consistent with your natural two-stroke kick cycle to this degree. By providing for more of a separate power and recovery phase, oxygen depletion is reduced, and the onset of fatigue is delayed. The result is that divers can kick continuously for longer periods of time.


Powerful Fins, Are They the Best Fins?


powerful fins, navy diverOne of the biggest areas of confusion regarding fins is the notion of “power.” Many divers believe that the more they can feel their fins, the more they’re getting out of them. And to capitalize on this belief, many fin manufacturers have responded by making longer and stiffer (more “powerful”) fins that fool divers into thinking that they are generating more propulsion with less effort.

However, the laws of physics don’t agree.

You are the power for your forward movement, the more you can feel your fins, the more energy you’re expending and the more you’re working for them, instead of having your fins work for you

“Power” is a measure of energy expenditure. More power requires more energy, and more energy requires more effort, not less. A 100-watt light bulb is more powerful than a 60-watt bulb. It puts out more light, but it also uses more electricity and costs more to operate.

The same with fins. What divers believe to be power in fins is really resistance. That’s what you feel. “Powerful” fins rapidly waste your energy supplies and actually transfer a much smaller percentage of the effort into forward propulsion than you think.

Since the name of the game in diving is to decrease energy use (which decreases oxygen consumption and increases bottom time), it makes sense to use more efficient fins, not more “powerful” ones, as long as they do the job of moving you through the water.

The fact is, no fins have power. You are the power for your forward movement, the more you can feel your fins, the more energy you’re expending and the more you’re working for them, instead of having your fins work for you. Force Fins are specifically designed not to be felt; Force Fins are designed to work efficiently for you.Extra Force Fin, Powerful Fin

And, for those of you who still want “power” our EXTRA FORCE FIN is the best fin.

The Extra Force Fin has the largest surface area for extra leverage under load. The way Master Fin Designer Bob Evans puts it, “You don’t fly a learjet to carry a herd of elephants. You fly a 747 or C130. The EXTRA FORCE FIN is our C130.