(5) The Back Sweep Phase

This phase produces the most drive through the water, it is fundamental when the athlete pushes back and propels forward quickly. From the angle created in the Front Sweep, the arms will then begin to extend at the shoulder and will horizontally abduct. The forearms flex at the same time even more until the hands are nearly touching under the abdomen, this will then make the arms circumduction backwards (Shown in diagram 1).

Diagram 1: This diagram shows the position of the swimmers arms in the water when the arms are moving down through the water to produce the back sweep phase of the stroke.

                              
Once both the arms and hands pass under the swimmers body the forearms will then rapidly extend and the arms will then abduct and hyperextend at the swimmers shoulder. This movement is synchronised with a second leg kick, in which the hips and knees go from being flexed to extending quickly, this kick is commonly known as the dolphin kick. The second kick should always be stronger than the first as it then can help propel the body roll forward. The hips should naturally sink into the water, which will then help the head naturally pop out of the water. During this movement the swimmer should take their breath in the stroke.

Execution of the Butterfly stroke will result in a linear motion of the body while generating the absolute maximum effort; therefore, the principles of biomechanics from each category are utilized. The construction of the maximum force that is required needs to use all of the possible joints to get the best result; the butterfly stroke beckons the use of all the major and minor joints in the body throughout both the upper and lower limbs. The joints include the hip joint, the shoulder joint, the ankle joints and the wrist joints. This skill uses Newton’s 3^rd Law of for every action there is always an equal and contrary reaction; to produce the maximum velocity, starting with the hip joint as the largest and then getting both the upper and lower joints limbs that descends from the shoulder to the wrist and from the knee to the ankle (Shown in diagram 2).

Diagram 2: The diagram shows the position of the swimmers hips in the water once the arms have gone back into the water ready to start this stroke all over again. This will help produce the back sweep phase of the stroke.

The major force responsible for the movement of the object is when the force applied with the upper limbs in the water. The direction of this force is changing the direction of the movement. The wrist joints and the ankle joints utilise the fifth principle of biomechanics which is stability in a given direction is directly proportional to the horizontal distance of the center of gravity from that edge of the base toward the given direction of movement; and with the water applying a force on the swimmers body. Newton’s Law of Reaction also explains this principle. 

Finally, the greater the force that is produced from the muscles which will cross each joint that is used in each stroke that is being taken, so that means the greater the change in speed of the object will be; utilizing the fourth principle of biomechanics which is stability is directly proportional to the area of the base on which the body rests, which is also the principle of impulse.