It is useful to see the throw as a system in motion. If the system is set up correctly from the beginning it will run as expected provided there are no breakdowns along the way. Many people do not realize how critical the entry of the discus throw really is. If the system is not set up correctly, it has virtually zero chance of success. Once the thrower has a good understanding of the full technique, she should spend time perfecting her entry every day.
A good entry in the discus begins with the setup in the back of the circle. The feet should be slightly wider than shoulder width apart in the back of the ring. If the circle is bisected, the feet should be straddling the line of bisection.
The toes should be flared out, and the legs should be bent so that the knees are over the toes. It is crucial to establish this knee angle before the entry of the throw, and strive to maintain it until the release of the discus. The back should be straight with a slight bend at the waist, as if the athlete is getting ready to jump. The chest should be up with the head held high so that it is in line with the spine.
The windup sets the system in motion. This is where the throw begins, so it is critical for the athlete to understand the purpose and the importance of the windup. Newton's first law states, "an object at rest tends to stay at rest until acted on by an outside force". After the initial setup of the throw, it is the windup that provides the force that gets the discus/system moving.
As the discus is wound back, it is important to remember the rhythm of the throw. There should be a slow to fast rhythm, so the windup should be the slowest portion of the throw.
How far the disc is wound back is based on thrower preference and flexibility, but is should be understood that the farther the disc is wound back the more kinetic energy is added to the system. The disc should not be wound back farther than 180 degrees. The head/eyes should remain fixed at 0 degrees during the windup.
At the entry to the throw, the discus is wound back and locked in place, arms are 180 degrees apart, head and chest are up, and eyes and chin stay aligned with the sternum. The right handed thrower will shift his weight from his right side to the left, while pushing the left heel toward the ring. The left foot and knee should turn to 90 degrees. The right foot should remain flat with the knee pushing away from the left.
The axis of rotation for this system should be from the ball of the left foot up through the left shoulder. Remember, the left knee should be pushing down over the left toe. The left arm should remain relaxed and extended, not breaking the plane of the left knee. At 90 degrees the thrower will work to push the left knee down, while the right foot remains flat and knees are pushing away from one another.
When the legs have reached their maximum stretch reflex, the right will come up. The thrower keeps the toe up with the leg long and knees wide as if getting on a horse. Remember the left foot is still at 90 degrees with the knee pushing down. Now the thrower aggressively kicks the right heel toward 90 degrees while pushing toward the middle of the circle with the outside of the left foot.
The long right leg acts as a lever moving about an axis, so as it kicks and the left leg pushes, the net result is for the thrower system to end up in the middle of the circle in the desired position. The entry and sweeping action add the majority of the force into the throw. At this point the stage has been set as to how the throw is going to continue.