Freestyle kicking is a simplistic complex issue. Many people can perform the task, but are unable to articulate the task. On the other hand, many people can articulate the movement, but can not perform the task. This simplistic complexity can be frustrating for many beginners, especially in Master's programs who have maladaptive bodies and muscles.
Freestyle kick should predominantly come from the hip, with minimal force production from the knee. Knee kicking causes high drag coefficients in the water. For this reason, freestyle kicking should only encompass 15 degrees of knee range of motion, but nearly 60 degrees of hip range of motion.
There are three muscles that require adequate mobility to perform freestyle kick.
1. Hip Flexors:To improve hip kicking, proper muscle length needs to be achieved. Short hip flexors (quadriceps, psoas) will prevent hip extension and cause an athlete to arch their back. Therefore, proper length of the hip flexors is mandatory.
2. Hamstrings: Tight hamstrings can cause flexing at the knee, therefore stretching this musculature is needed. Improper stabilization of the lumbar spine and pelvis can cause decreased hip mobility (mobility and stability go hand in hand, if one is inadequate the other will suffer). Therefore, strong abdominals and lumbar stabilizers (multifidus) is mandatory to perform proper kicking.
3. Calves: The calf is composed of the soleus and gastrocneumius. The gastrocnumius crosses the knee joint and if tight can cause flexion of the knee. Tightness of the calf can increase knee flexion during the up kick.
To improve muscle length, active mobility drills, passive stretching and manual soft tissue mobility can be utilized. The idea is to change the length prior to swimming, use this new length while swimming, then improve muscle length after swimming or on off days. There is conflicting evidence on the time best suited for stretching, but anecdotal evidence various experts stress these ideas.
Enjoy, have fun