Draw water upward
first step
In butterfly stroke, the legs are naturally close together, and the heels are slightly separated into "inner characters". In the last stroke cycle, when the leg is kicked down, the foot is at the lowest point, the knee is straight, the hip is lifted to the water, and the hip joint is bent about 160 degrees.
Second step
Then the legs swing straight up and the hip joint gradually expands. When the thigh rises to be in line with the trunk, the waist, abdomen and buttocks begin to sink and the thigh begins to press down. When the thigh is pressed down, the foot and calf continue upward due to inertia, and the knee joint naturally bends.
Third step
As the thigh continues to accelerate downward, the degree of knee flexion increases until the foot is raised close to the water surface, about 4 ~ 5 cm underwater. At this time, the buttocks sink to the lowest point, and the knee joint bends at an angle of1/kloc-0 ~130. At this time, the upward pumping is over.
Draw water downward
first step
With the acceleration of the thigh pressing down, the foot and calf are accelerated by the thigh, and hit backward and downward until the calf and foot draw water downward, until the knee joint is completely straight and the foot is at the lowest point.
Second step
Pulling water down is the process of stretching your knees. The calf and foot accelerate to draw water back and forth, just like a whip thrown at the bottom of the pool. When the ankle joint bends downward, the sole of the foot rotates inward, and the flexibility and flexibility of the ankle joint play an important role in the effect of fetching water.
Third step
Downward pumping is the main stage of generating propulsion, which should be completed quickly. The downward drawing of water ends and enters the next drawing cycle. There is no obvious boundary between getting water up and getting water down: the calf and foot have not finished getting water, and the thigh has already started getting water down; Before the legs and feet kick down, the thighs have begun to swing up and enter the upward kick. The movements of the trunk and legs are coherent, forming a wave motion.