video clips.
Swimmer (A.) below has 60 degree ankle range of motion (when foot is flexed forward, top of foot is parallel with front of shin). To orient the top of the foot to a propulsive angle of attack for the down-kick, the swimmer must bring the knee down first. Swimmer also has limited upper body flexibility which limits hip movement. Less hip movement requires additional knee bend to do the kick. Excessive knee bend exposes the thigh to increased drag which cancels much of down-kick propulsion. This swimmer also has average knee joint range of motion (knee does not move back past straight when leg is straightened at the knee). Swimmer gains propulsion from the underside of the foot on the up-kick but gains no propulsion from the back of the calf. This swimmer does not have a very effective fly kick.
images\fly man\Flyman60stiffwmv.wmv
Swimmer (B.) below has 60 degree ankle range of motion (when foot is flexed forward, top of foot is parallel with front of shin). Must bend at knee to get any propulsion from the down-kick. Swimmer has good upper body flexibility which brings good hip movement and requires a little less knee bend than swimmer (A.) above. Swimmer (B.) has average knee range of motion (knee does not move back past straight when leg is straightened at the knee). Swimmer gains propulsion from the underside of the foot on the up-kick but gains no propulsion from the back of the calf. the down-kick, the swimmer must bend more at the knee.
images\fly man\Flyman60wmmed.wmv
Swimmer (C.) below has it all. Greater than 60 degree ankle range of motion, very little knee bend required to get top of foot to propulsive angle of attack. Excellent upper body flexibility provides 2 benefits: 1. less knee bend required to set up the down-kick and 2. swimmer is able to smoothly undulate the surfaces of the body from top of shoulders, front and back of the chest and abdomen, front and back of the pelvis on down to the knees so some additional propulsion is gained from these surfaces. Exceptional knee joint range of motion gains additional propulsion off the back of the calf on the up-kick. This swimmer is much more efficient, can go faster for less effort because the movements cause less drag than the movements available to swimmers A and B