The flutter kick is often discussed but little taught. Common phrases include “kick from the hip”, “don’t let your knees drop”, “don’t kick with your knees”, “keep your kick in the shadow of your body”, and so on. But these tell us nothing about how to actually do it. Here is Sun Yang swimming in the 2012 London Olympic games.
He has not started his kick. His left leg is straight and extended well above his hip, as if in a Superman position, with his heel just touching the surface. The leg must be recovered in a lock-kneed position, perfectly straight, or it will create drag. This requires great hip flexibility and strength. His same-side arm is fully extended, and he is breathing. Most amateurs let their legs drop below hip level when breathing and this creates drag. Do a Superman on the floor and where do you feel it? In your back and hips. Lifting straight legs up, taking your thighs off the ground, requires constant hip contraction. For most adults, this is where they must start, by working on their “upkick” or recovery motion, constantly squeezing the hips to keep the legs high. Once this is accomplished, only then may they begin to kick in a small range of motion.
He begins his kick with a slight push down of the knee (driven by the hips). His foot is still high but is getting ready to power down as his knee extends. In this shot you can see that his quad is a bit lower than his hip for a split-second. All this begins as he is making his catch. It is the timing of a tall swimmer who fully extends out front every stroke.
He snaps his knee right, extending it, as the catch is completed. This provides some force to help him rotate his hips and gives leverage for his pull. After that movement however, the leg needs to be out of the way, and it is – perfectly straight behind him, in line with the left arm that’s about to pull. His knee has actually moved UP as his kick finishes DOWN, so there is little net movement of the entire leg downward. With good ankle flexibility most of the force will be backward. There will be no drag caused by his leg during the pull.
His left leg is still straight as he pulls, and creates no drag. His hips are at the surface (you can see them just breaking the water line) which is critical to reduce drag. You can see his right leg fully recovered (and straight) above his hips and breaking the surface. He’s as streamlined as you can get, so the power of his left arm pull is all going toward moving him forward vs. overcoming lower body drag.
Left leg is still straight… You can see the right knee begin to drive down to start that kick.
This is where many amateurs create drag. Instead of maintaining a straight leg after they kick, their hamstring overreacts and pulls the foot up toward the surface. This creates tremendous drag against the calf and the back of the foot, and leaves the knee bent and below the bodyline. This is especially important for a 2-beat kick since it is mostly arm driven and any leg drag is highly detrimental.