(3) Catch Phase

The Pull/Catch/Entry phase 

The catch phase of the butterfly stroke begins at the point where the swimmers hands enter the water at the end of the recovery phase through fluid dynamics. The crown of the head with your shoulders and hips horizontal should lead your body. 

Hands are in a downward lateral movement with arms extended forward in the front of the swimmers head, creating the “Y” shape. This is a pull like movement. Elbows can be, with both arms at shoulder width apart, wrists are flexed down and palms facing backwards towards the feet and slightly outwards with hands almost in a vertical position, pulling backwards in a “S” shaped pulling pattern (shown in the diagram 1 and video 1). This movement is important because it is the entry point of the hands into the water that forces the body through the water coupled with the wave curve of the body and dolphin kick as it influences the swimmers drag. (Blazevich, 2012).

Diagram 1. This swimmer has come from the recovery phase into the catch phase/Entry phase and shows the correct technique of hands and arms entering the water just before moving towards the front sweep creating the keyhole/ "S" movement. 

Video 1. This video shows the swimmers ams entering the water in the catch phase. 

Both hands, with fingers together, penetrate the water simultaneously by shoulder rotation with both arms and palms remain facing in the direction of travel close to the body. The elbow should bend to about 90-degree angle to provide the extra power required to increase angular velocity. The hands sweep in a circular movement similar to breaststroke, but in a downward path into the next phase of the front sweep as you can see in diagram 2. The technique heavily relies on the upper body muscle groups that maximise the force production of the arms are in the trapezoids, rhomboids, deltoids and triceps. The core muscles are of vital importance to a swimmer's power, particularly in the butterfly stroke; these muscles have been illustrated in diagram 3. 

Diagram 2. This diagram shows the positions of the swimmers arms in the water with elbows flexed and hands flat with fingers together in a sculling position. This leads into the front sweep phase.

Diagram 3. This diagram highlights the swimmers muscle use in the upper body. 

The abdominal muscles provide the strength to lift the upper torso out of the water, and then curve in to return. As this point the swimmers head, torso and gluteal region are propelled above the water to produce maximum velocity and power in the shoulder rotation and force production.As the shoulder rotation is a quick and continuous movement it helps the swimmer increase impulse momentum with the amount of force applied to accelerate the swimmers performance. 

All joints of the kinetic chain simultaneously extend in a single movement creating higher cumulative forces to result in the swimmers body to move in a specific wave like movement through hip and shoulder rotations. This is important in the dolphin kick that butterfly swimmers use.

By having correct arm movement and technique the upper body needs momentous strength and keeps the body, center of mass and leg movement (that is referred to as a dolphin kick) balanced, shown in Diagram 4 (Blazevich, 2012, Seifert, Delignieres, Boulesteix & Chollet, 2007).

Diagram 4. This diagram shows the swimmers body in a undulate motion similar to a wave curve and dolphin like kick. 

At a high swimming velocity the catch phase of the butterfly stroke is important as the hands prepare and is used as a lever to propel the swimmers center of mass forward, which is the swimmers largest inertia values forward through the water. The swimmers hands velocity is the most propulsive phases of the butterfly stroke sequence. At hand entry of this phase the swimmers head and body are propelled through and up above the water creating wave drag. If butterfliers are able to decrease their hands velocity during entry, it is possible for the swimmer to reduce the momentum of the swimmers center of mass and decrease wave drag to help accelerate the swimmers forward momentum.This is associated to Bernoulli's principle of a swimmers hand moving through the water as swimmers hands fluid pressure and velocity to aid swimming propulsion.(Averianova, Nikodelis, Konstantakos & Kollias, 2016, Barbosa, Fernandes, Morouco & Vilas-Boas, 2008, Blazevich, 2012).