(1) The Biomechanics of the Butterfly Stroke

The aim of this assignment is to quantitatively and qualitatively research the optimal biomechanics for a sport skill that will be reported with our findings using an online blog. The sport skill that has been chosen for this blog is the butterfly stroke. 

The Butterfly Stroke is a swimming stroke that is swum on the breast while both of the arms moving simultaneously and then it is followed by the “dolphin” kick. This stroke is different to the other three swimming strokes as the butterfly stroke is the most difficult on for beginners to learn. 

The purpose of this skill is to move one’s body position in the water while trying to be as successful and effective when continuously executing the skill in order to minimize the time interval. So the fastest to complete the distance in a competitive race wins.

The butterfly stroke is possibly the most challenging and demanding swimming stroke compared to freestyle, breaststroke and backstroke as the butterfly stroke is very complex and is tiring and difficult to produce (Barbosa, Fernandes, Morouco, P & Vilas-Boas, 2008). This stroke can be broken down to four phases, the catch phase, front sweep, back sweep and recovery. This blog will look further into the biomechanics of these four physical phases. In a swimmers perspective there is also the four swimming phases of the starting phase, swimming phase, turning and finishing phase.  These phases can be seen in diagram 1

Diagram 1. This diagram shows the simulations movements of the swimmers body submerged and propelled above the water coupled with arm rotations, hip flexes and leg kicks that accelerate the swimmer through the water.

The butterfly swimmers arms, legs and torso are a continuous and simultaneous movement that requires the swimmer to have significant upper body strength, correct use of technique that keeps the body balanced and generates maximum effort and momentum. As well as body preparation all joints in the kinetic chain simultaneously extend in a single movement creating higher cumulative forces and torque that results in higher overall force. By looking at this sporting skill this blog can break down and look at a swimmers swimming position, velocity and acceleration through technique as well as Biomechanical qualities that optimise the swimmers performance while in the water are fluid dynamic and hydrodynamic –Drags and Hydrodynamic propulsion and the Bernoulli effect (Blazevich, 2012).

Both videos below show and demonstrate the biomechanics of the butterfly stroke. Through simultaneous movements of the arms, legs, breathing and body to counter balance each other to provide propulsion. Both videos give different perspectives of the biomechanics and techniques of the butterfly stroke (Butterfly Technique, 2016, Basic butterfly stroke technique, 2016).
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(2) Starting block - Potential Energy

Benefits of a good start 
Potential energy is the energy associated with position. In competition swimming, butterfliers start on the starting blocks. The starting block is where swimmers have the potential to position themselves in such a way that would enforce their beginning movement into the water at a certain velocity. At this starting point on the blocks, swimmers can have the interval to apply force and dictate the velocity at which they will travel at the start of their dive (Blazevich, 2012). There are three specific dives swimmers use, the grab start, the track start and the slingshot start. Individual swimmers have their own technique and have different reaction times so all start positions will differ. Hand and foot placement coupled with time is crucial at the starting point. The swimmers starting position benefits on their canter of mass placement and technique to increase force momentum and move inertia with little effort when the body is propelled forward into flight. Swimmers can use these positions to better start themselves. Thigh is close to chest and the rest of the leg at a 90 degree angle with center of mass aligned in the middle of the body. Lags can be in a starting block position similar to track or with both feet forward with toes and fingers curled around the edge of the starting block as leverage points. These positional changes will maximise the potential energy going into the dive.

Diving off the block

The swimming dive start is highly linked to overall performance during competition. Actually the start can contribute to anywhere between 0.8 – 26.1% of a swimmers total race time and also the distance of the race. The swimming dive start is defined as the time from the starting signal which is either a gun or beep, to which the centre of the swimmer’s head reaches 15m down the pool (Tor, 2014).

The swimming start is broken down in three phases (Shown in diagrams 1, 2 & 3):

1.     On-block

2.     Flight

3.     Underwater

The average percentage contribution for each phase of the start for elite swimmers can be 11% (0.74s) spend in the on-block phase, the flight phase of a swimmer is 5% (0.30s), for the underwater phase a swimmer would be under for 56% (3.69s) and finally only 28% (1.81s) would be swimming.

Diagram 1:

On-block phase: the time from the start signal to when the swimmer’s toe leaves the block.

Diagram 2:

Flight phase: the time from when the swimmer’s toe leaves the block to when the swimmer enters the water.

Diagram 3:

Underwater phase: the time from when the swimmer enters the water to when the swimmer’s head breaks the surface of the water.

The underwater phase is the longest phase of a swimming start as it can account to about 95% of variation of the start time. It is also the most decisive when it comes to determining the efficient overall start performance, as it is the fastest that the swimmer is traveling through the water.

A perfect dive will not always come from the fastest starter or from the swimmer who enters the water first, it will come from the ones that can maintain a high velocity once they have entered the water. Before a swimmer can hit the water they need to learn the maximize their take-off horizontal velocity while also trying to reduce their reaction time in the process. There are numerous factors that can affect a swimmer after they enter the water which can verify how much a swimmer is maintaining their velocity during the underwater phase and they include:

• Having a good streamline
• Starting the dolphin kick after about 6 metres
• Generating a propulsive kick by using only the feet during the underwater phase 

Another way to get a good start also depends how deep the swimmer dives into the water, if they dive too deep then they will spend more time making their way up to the top of the surface and if they dive too shallow then they will experience high drag forces on them. Also kicking early can also increase the amount of drag on the swimmer.

The 15 metre rule 

After both the starts and turns, a swimmers head must break the surface at a distance no greater than 15 metres. If a swimmers head resurfaces after the 15 metre mark, then they are disqualified as they have broken the rules. The rule came into place as underwater swimming gained popularity while swimming but a large number of athletes began suffering from oxygen starvation and so the 15 metre rule got invented and put into place.