Why does this question matter?

As the swimmer moves through the water momentum is built up, and at the wall the swimmer must reverse their body and build momentum back up again. Maglischo and Sanches found that in freestyle events swimmers spend between 38% and 50% of their competition time executing turns in short pool competitions over distances that vary from 50 m to 1500 m.  Maglischo also found that by optimising the technique of the freestyle turn times can be reduced by at least 0.20s per lap (as cited in Araujo et al., 2010, p. 1175). 0.20s is quite a significant time to take off a lap, and it therefore shows how vital executing a quick and efficient turn during freestyle is for success in both swimming races and personal time-trials.

An understanding of the biomechanical principles of the freestyle tumble turn, and knowing how to apply them allows a swimmer to optimise the use of their body during the movement phase. I hope that by reading the information in this blog the swimmers amongst you are able to consider some of the biomechanical principles of the turn and how they can be used to improve your performance in the pool.

                                                                    The above video shows how the Australian Institute of Sport uses the 'Wet Plate' system to biomechanically analyse and improve the starts and turns of the Australian Swim Team.

What are the biomechanical principles of the 'preparation' phase of the turn?

Preparation for the freestyle turn occurs well before the wall is reached and being aware of the biomechanical principles of the preparation phase of the turn can set the swimmer up for a time and energy efficient transition between laps. Blazevich (2012, p. 164) explains that the forward speed of the swimmer is dictated by two factors: 

           1. Forces resisting motion – drag

           2. Forces causing motion – propulsion

Reducing drag and increasing propulsion in the preparation phase will increase the speed of the swimmer and therefore increase the speed into the turn. There are three forms of drag:

          Wave drag

          Form drag

          Surface drag

These can all be manipulated to increase the speed of the swimmer, and the positioning of the hands can be altered to increase the propulsion. This will be discussed below.

As the swimmer approaches the wall a breath should be taken and a full stroke cycle should be completed. The turn should begin after the last stroke of the cycle. The turn is initiated by the flexion of the head and spine along with the dolphin kick. This drives the head and shoulders down and raises the hips. The forward roll is then able to occur due to the torque produced by the dolphin kick and the increased resistance of the head and shoulders as they move out of alignment with the rest of the body. The upper body flexes about the hips, and the knees are tucked close to the chest to reduce the distance from the axis of rotation and decrease the amount of inertia (Lyttle, 1999, p. 8). 

How can this information be used?

  Wave drag is present at the interface of the water and the air, as the swimmer pushes through water and the drag is greatest when the wave distance equals the length of the body. To reduce wave drag, Blazevich (2012, p. 158) suggests increasing the effective body length by stretching the arm in front of the body at the end of the recovery phase (before propulsion). The arm may also help in dispersing the oncoming flow of water, reducing the wave build-up hitting the surface area of the swimmer’s head and therefore reducing wave drag.

   Wave drag: waves build up at the front of 

   the body during swimming, creating drag.

Form drag is the drag associated with the surface area and the shape of the swimmer. This form of drag can be reduced by keeping the surface area that is exposed to the water at a minimum. The head should be kept down and the swimmer should be conscious that the larger the kick the larger the frontal surface area becomes. Additionally, keeping the waist high and the legs aligned with the waist minimises the pitch angle, therefore reducing drag and maximising speed.

Form drag: having the body aligned during the

 swim reduces the surface area of the body and therefore 

reduces form drag. When the body is unaligned the 

surface area is greater, therefore creating more drag. 

  Surface drag is caused by the friction of a fluid on the surface of an object. This form of drag in swimming is typically caused by the material and size of the swimmers and the presence of body hair. Hairless skin has a lower friction coefficient than Lycra or cotton in water and traditional, yet still widely popular, drag-reducing techniques have involved shaving the limbs and head in conjunction with wearing a swimsuit that covers the minimum amount of the torso (Blazevich, 2012, p. 163). While high performance swimsuits are widely popular in professional swimming their use raises questions about fairness in the pool and is dictated by strict guidelines as outlined by FINA - the international authority on swimming. 

                                                                               

   This short video shows how swim wear company Speedo has incorporated biomechanical principles related to drag to create a new swim suit that meets international guidelines.   

  However, drag is not always a bad thing. Blazevich (2012, p.169) writes that the force of propulsion into the freestyle turn can be harnessed by increasing the surface area of the hand and arm and therefore increasing drag. This is achieved by a straight arm path and slightly spread fingers. Spread fingers increases surface area as the flow of water is impeded as the volume of water passing through the hand is increased. Additionally, flexing the elbow and wrist downwards in the propulsive phase of the stroke, as opposed to keeping a straight arm, ensures the horizontal forces are optimised, the greatest amount of water is 'caught' or 'dragged' and propulsion is maximised.

What are the biomechanical principles of the 'contact' phase of the turn?

The contact phase involves planting the feet, bending the knees and driving with the thighs to generate thrust in the opposite direction. Lyttle (1999, p. 9) explains that the wall contact time has two force production phases: passive and active. The passive force production phase involves the wall impact and the countermovement which is the lengthening of the quadriceps (an eccentric contraction). The active force production phase consists of the shortening of the quadriceps (a concentric contraction) in order to create velocity away from the wall. The forceful extension about the knees and plantar flexion of the feet in the horizontal direction occurs in the active force phase.

A study by Araujo et al. (2010, p. 1180) found that a turn executed with angles of knee flexion between 100°and 120°provides the most favourable peak forces to generate impulse. This angle allows for a time efficient turn without an exaggerated application of force and the subsequent unnecessary expenditure of energy. 

How can this information be used?

The key to this stage of the turn is the planting of the feet. If both feet aren't confidently planted on the wall the potential to generate thrust in the opposite direction isn't totally harnessed. The other consideration of this phase is to not waste time rotating the body back onto its front when coming out of the turn. Optimise the high velocity present in the turn by pushing off in the position the body is already in, and move the body back to its front when travelling in a streamline position away from the wall. 

The video below shows what to avoid in this phase of the movement pattern. 

What are the biomechanical principles of the 'follow through' stage?

The follow through phase begins with a streamlined glide and this is an integral component of the swim turn as the velocity of the push off is greater than swimming speed, and strokes should only resume once the velocity has decreased to swimming speed. There are two determining factors that affect glide performance:

·         The initial wall push-off velocity

·         The hydrodynamic drag that acts to slow the swimmer down

The follow-through phase is affected by the velocity of the glide, body form, degree of streamlining and the glide depth (Little, Lloyd, Blanksby  & Elliott, 1999). A later study by Blanksby, Elliott, Lloyd & Lyttle (2000, p. 801) acknowledged that a widely held opinion is that the lateral streamline and lateral dolphin kick position produces faster turns. However, their study showed that no one kick resulted in any significant advantage over the other and no significant difference was found between the prone and lateral streamline glides at any speed.

In freestyle, most swimmers take their last breath one stroke cycle before reaching the wall. In his study on the relationship between the breath holding times and the biomechanical events of the turn Craig (1986, p. 405-406) observed that the breath holding time was longer in the freestyle events than in butterfly and the backstroke and this was due to the necessity of beginning the breath apnoea before reaching the end of the pool. The relationship between the biomechanical aspects of the turns and the gas exchanges during the brief period of breath holding suggests that swimmers can maximise the period of increased velocity of the push off without being limited by the consequences of the apnoea. While the period without a breath can be distressing relief can be expected after the first inspiration of air and swimmers should utilise optimal biomechanical manoeuvres for turning without concern for the physiological stresses associated with the necessary period of breathing apnoea.

How can this information be used?

To minimise the hydrodynamic drag on the body coming out of the turn a number of technique parameters can be manipulated.

 -   To optimise the velocity of the glide the body should adopt a streamline position. The arms should be extended in front of the head, with the head tilted down to minimise wave and form drag. The waist and hips should be kept high to minimise the pitch angle, and the legs should be kept together with the feet pointed to maintain body alignment.

 -   In regards to glide depth Blazevich (2012, p. 159) explains that wave drag is present at the interface of the water and the air as the swimmer pushes through the water. At the point of the turn wave drag increases, particularly when multiple swimmers are turning. Shallow gliding can result in contact with the wave drag and this can slow the swimmer down. However, gliding too deep will also slow the swimmer down and consume a high amount of energy as the swimmer makes their way back to the surface.

 -   Blanksby, Elliott, Lloyd and Lyttle (2000, p. 801) determined that no one kick or position of the body during the streamline phase was more advantageous than the other. However, when considering what kick to exit the streamline phase with keep in mind that the amplitude of the leg kick should be as small as possible as increasing the kick amplitude increases the frontal surface area and therefore increases form drag. Regardless of what type of kick is preferred to exit the streamline with it should be a small, yet powerful, kick as this reduces wave (and total) drag.

 -   In regards to breathing, push through the pain barrier. The last breath should be taken before the final stroke cycle and another inspiration should not be made until the stroke cycle has resumed. Harnessing the momentum of the turn should be the first priority, and the faster the turn is completed the faster breathing can resume!