Whether you're a sprint specialist, long-distance swimmer or triathlete, proper kicking techniques can greatly improve the efficiency of your freestyle stroke. Racing swimmers can generate substantial force with a good kick. Triathletes might want to "save" their legs for running and biking, but proper kicking form greatly reduces the underwater drag generated by their legs and helps to control their body position during the stroke. Regardless of your swimming specialty, improving your flutter kick will enhance your speed in the freestyle stroke.
Improve your ankle flexibility for a stronger kick. Much of the propulsive force of your kick is generated by the top of your foot pushing against the water. The more range of motion you have in your ankle and lower foot, the more powerful your kick. Swimmers with the strongest kicks can point their feet directly in line with the their lower legs -- a 90-degree angle to the normal position of their feet -- and sometimes even farther. Perform daily ankle stretching exercises with the aid of a strap board or an incline board until you can achieve a straight "toe point" to generate maximum kicking force. When you swim, remember to flex your ankles as much as possible by trying to point your toes at the wall behind you.
Generate more power with each kick by strengthening your hip flexor muscles. Most of the force in your kick is generated by your hip muscles. Vertical kick drills can strengthen your hips and improve endurance. In the deep end of the pool, simply stand upright and flutter kick to push your body as far out of the water as possible. Beginners can use their hands for balance, but ideally you perform the drill with your arms streamlined or crossed on your chest. Kick for 45 seconds, then repeat the drill after a one-minute rest interval.
Focus on keeping your legs relaxed and loose. Relaxed, "long" legs transmit more force from your hips to the water, so it's important to minimize knee bend in your freestyle kick. Too much knee bend results in a kick with wasted motion out of the water. Perform deep leg kick drills to minimize knee bend. Swim with a practice float to support your hands, and use only your kick. Allow only your heels to break to the surface and concentrate on keeping your legs as straight as possible during your kick recovery.