Because regular foot fins are on your feet, they slope your thighs down in the water when you swim. You feel the extra drag from the water pushing against your sloping thighs. This thigh drag wastes your energy. So foot flippers don’t help to lift your thighs to streamline your kick. Quite the opposite. Foot flippers sink your thighs and work with different kick to good swimming without fins.
Many swimmers know they should have their thighs horizontal. But still their thighs keep sloping down when they kick. Wearing shinfin
It helps if you already have enough hip joint movement range to straighten your thighs, at least in line with your upper body. If not, then doing stretches on land can help to increase your range of hip joint movement. Swimming with shinfin
Now you can have fins for extra speed and have your thighs horizontal for streamlined swimming!
See all faqs about smooth forces for faster swimming.
Go to main article for Smooth Fins.