Leg fins help to lift your body horizontal. As they lift your knees, your thighs, hips and torso lift too. So they lift your entire body into a more horizontal position for better streamlining. This reduces water drag and increases your energy efficiency.
Regular foot fins make you bend your knees too much. They sink your hips and thighs too low in the water. So they slope your body down in the water too. Then the water flow hitting the front of your body and thighs causes too much drag and wastes your energy. Foot flippers sloping your body and thighs downwards, causing drag, is a very common problem.
In fact, even for swimming without fins, many people (other than good swimmers) still have their body sloping down in the water. This increases drag and makes it much harder and less enjoyable to swim. If you feel like you are poorly streamlined and wasting energy, then your body is probably sloping down in the water.
Leg fins lift your body because they attach to your legs. This means that the water flowing over the fins straightens and lifts your knees. Your higher knees lifts your thighs and straightens your hips too. So your whole body becomes more horizontal and streamlined. These fins do all this even at slow speeds.
Now you can have fins that lift your body horizontal and streamlined for less drag, higher efficiency and more fun swimming!
See related FAQ about how leg fins give you a smooth streamlined kick.
See all FAQ about why leg fins are the best swim style fins.