Biomechanical principles

The pre-execution phase

The biomechanical principles in play during the volleyball spike can be broken up into sequential parts of the skill, these are defined as the pre-execution phase (otherwise known as the run up), the jump and arm swing, the moment of contact and the follow through. Athletes who wish to produce an optimal volleyball spike must build speed and momentum very fast in a very short distance (Gaudet, 2014). This can be achieved by the athlete building as much horizontal velocity as possible during their running in approach before leading into a spike. Leaning the body slightly forwards will contribute to an increase in acceleration as it enables to engage their leg muscles, in particular the hamstrings, quadriceps and gastrocnemius muscle groups to push off the ground and accelerate them forwards (Gaudet, 2014). Also, decreasing the contact time between the feet touching the ground reduces the average applied forces per stride and therefore allows the athlete to be able to accelerate a lot faster (Gaudet, 2014). This shows how important momentum and speed are to a volleyball run-up approach, even though it only consists of two to four steps, the faster the athlete is moving and the more momentum they have is vital to achieve a high vertical jump (Abendroth-Smith & Kras, 1999).

Experts have argued that the four step approach to spiking is more effective than the two step spike approach because four steps allow the athlete to build more momentum resulting in a significant increase to their vertical jump height (Abendroth-Smith & Kras, 1999). However, a two step approach is a faster approach meaning it is more beneficial if the athlete has less time to perform the skill. For optimal performance, athletes weight should be slightly leant forwards at the beginning of the spike approach, as the athlete is taking their steps they must ensure they are quick and light on their feet (Gaudet, 2014). To further assist the transition between horizontal and vertical momentum the athlete should make their last step longer than the other run up steps due to the transfer of weight before the jump, as seen in figure 1 (Abendroth-Smith & Kras, 1999)

The jump phase

The jumping phase in the volleyball spike sequence plays a significant role in enabling the shot correctly. The athlete’s vertical height of their jump helps them to determine appropriate shot placement and the ability to achieve the best angle on the volleyball during an attack phase by providing them more time in the air to make their decision (Abendroth-Smith & Kras, 1999). This is made successful by the athlete’s legs straightening from their bent position just after their feet leave the ground. Vertical momentum is conserved in the upwards direction by straightening and extending the legs at the peak height of the jump. The centre of mass of the volleyball athletes body is moving in a downward motion due to the effect that gravity has on objects, however the upper body of the athlete is moving upwards due to the straightening of the legs. The result of this is the athlete being able to momentarily hang their centre of mass in the air (Magias T, 2016). In order to achieve a successful jump a volleyball player must have quick and synchronized coordination of their body movements. When conceptualizing the biomechanical principals which optimise athlete jump height and performance numerous factors are concerned such as inertia, gravitational force, equal and opposite force reactions and momentum transfer.

Generating enough force to propel an athlete high enough to perform the volleyball spike involves the transitioning of kinetic energy from traveling horizontally in motion to vertically in motion. To better understand this principle one must first analyse Newton’s three laws of motion. Newton’s first law is more commonly known as Newton’s law of inertia, which states that an object will remain at rest or will continue to remain in motion at a constant velocity as long as the force of acting upon that object equals zero (Blazevich, 2010). The tendency to resist the changes in the state of motion is described as the act of inertia, in order for an athlete to overcome their bodies inertia they must convert their state from being at rest to traveling in a vertical motion (Physicsclassroom.com, n.d).

This then leads to Newton’s Second Law:

Newton’s Second Law refers to velocity, this law states: ‘the acceleration of an object is proportional to the net force acting on it and inversely proportional to the mass of the object (F = ma)” (Blazevich, 2010). Force is essential for a volleyball athlete to overcome inertia. The athletes body mass (the amount of matter in an object) and the weight (the effect of gravity on the matter) of an athlete determines the relative importance of inertial and gravitational forces (Change, Huang, Hamerski & Kram, 1999). For example, an athlete with smaller and lighter body mass will find it easier to overcome gravitation forces and they will feel a lighter effect of inertia. This therefor means the lower the body weight and body mass of the athlete, the better that athlete can accelerate their body under given forces, this results in a maximized jump due to the less force required to overcome inertia (Blazevich, 2010). Correctly applying these forces lead into the introduction of Newton’s third law.

Newton’s Third Law of motion states that for every action there is an equal and opposite reaction (Blazevich, 2010). This is seen during the jumping up phase of the volleyball spike where the athlete applies force downwards to the ground in a vertical direction. If the force which the athlete produces is enough to overcome inertia, the ground will in turn exert an equal and opposite reaction which results in the athlete being accelerated forward thus contributing to a successful volleyball spike (Pick, 2013).

                 

The arm swing phase

However, an optimal jump technique for a volleyball spike does not solely rely on the lower half of an athlete’s body, the upper half also contributes majorly to a heightened vertical jump. Hsieh and Heise (1997) found that the swinging motion of the arms during the jumping phase acts as one of the most important factors contributing to the jumping height during the volleyball spike. The athletes preferred arm is initially situated behind the body in a hyper-extended position, this is to prepare the arm for the best position to achieve enough momentum needed to swing the arm forwards, upwards and then downwards (Hsieh & Heise, 1997). During the upwards acceleration phase the arms push against the inferior parts of the body in order to increase the downward force which acts upon the floor therefore creating a greater counter reaction on the athlete. An athlete’s centre of mass is dictated by the amount of vertical momentum generated at take-off (Ding, 2004). The arms momentum and position, as well as the athlete’s trunk rotation and flexion also play an important part in the balls velocity (Moellendorf, 1993). This generation of force started by the arms, transferring through the body and finishing as the legs are fully extended is often referred to as the summation of forces.

In order for an athlete to achieve optimal performance during their arm swing they should swing both arms back equally or above their head, this will provide them with a lower centre of gravity and a smaller centre of mass (Blazevich, 2007). A low centre of gravity allows the athlete to distribute their weight evenly when spiking a volleyball, this further assists the transition between traveling forwards and jumping upwards by keeping the athletes weight over their feet without leaning to far forwards (Blazevich, 2010). An athlete can distribute their weight more evenly in all directions (not just up and down) by crouching down low when planting both feet before jumping upwards (Blazevich, 2007).

When analysing the arm swing, we refer to the biomechanical principle known as the kinetic chain. Blazveich defines the kinetic chain into two main categories, these are known as push-like and throw-like movements. The throw-like movement assists in directing the arm at the beginning of the swing, the shoulder then extends followed by the elbow and wrist which are flexing throughout the movement (Blazevich, 2010). The extension velocity of the hand and fingers increases when ball contact is about to be made, this results in a high ball release velocity (Blazevich, 2010). During the wind up phase in the arm swing the internal rotatory muscles within the arm act concentrically (Dangelmaier & Coward, 2001) This generates more energy by increasing the range of motion the arm can swing, which in turn is then transferred to other body parts which assists in the improvement of the overall vertical jump performance.

The arm swing is important because it is the last opportunity the player has to increase their force and power before contacting the ball. Also this is the last chance to effectively control and use the momentum and acceleration that the athlete has accumulated from the run up phase as well as the force produced during the vertical jump by the lower body (Hsieh & Heise, 2006). The physiological structure of a volleyball player’s arms are built similarly to their lower half of their bodies in that the mass of their length and mass can help to create a greater volleyball spike force (Blazevich, 2010). A combination of both long and short levers allows for the athlete to apply maximum force and acceleration to the volleyball during the arm swing. Long levers increase the applied force an athlete is utilizing whereas short levers are suited for fast and accelerating movements. The spike action uses both of these levers, the radius and ulna make up the long lever and the wrist resembles the short lever. Long arms are best suited for increasing angular velocity as well as the ability to rotate around an axis. Therefore, to achieve a higher rate of velocity by increasing the distance between the axis of rotation (elbow joint) and the point of contact (hand) (Blazevich, 2010).

Elite athletes can benefit extensively by understanding the biomechanical contributions that make up a sport skill such as the volleyball spike. Leonel Marshall is an example of an elite volleyball player who has a vertical jump of 127 centimetres (50 inches), this shows how he demonstrates the effectiveness of mastering basic biomechanical principles. Marshall has become a major asset to the team due to his significantly increased jump height, this is beneficial in game situations as it allows for more time in the air to hit the volleyball with a more accurate angle of release and speed. Sports development coaches are constantly analysing and examining athlete performances during and after games to look for improvements in technique in order to achieve optimal performance.   

The moment of impact and follow through

When a team is performing a strike in a volleyball game, the opposition can put up an intimidating block where a player jumps up, usually two to three and a half metres high, attempting to stop the ball from entering their half of the court. Therefore, in order to produce an effective volleyball spike the ball must be contacted high above the athlete’s head, this gives the spiker the best chance to hit the ball either through or over the top of the block (Mann, 2008). At the point of contact, the athlete’s wrist should be loose and floppy, however, the hand still needs to make hard contact the ball. An impulse-momentum relationship can assist the outlining of body movements used when performing the optimal volleyball spike. When the volleyball has been set to a spiker the ball moves through the air with minimal momentum very slowly, therefore, there must be a greater force acting upon it for the ball to increase momentum (Blazevich, 2007). The momentum of the volleyball has an equal force to that which has been exerted upon it, multiplied by the time taken for the force to be exerted (Blazevich, 2007). This means that the less contact time between the hand and the volleyball results in the greater force applied to the ball. The force created in the spike comes from the rotation of the shoulders and the leg movements made in the air and is transferred into the ball when the Athletes hand makes contact.

If the athlete chooses to make contact the ball with a floppy wrist the ball will generate top spin and will dip down towards the ground faster. Because the volleyball spike is completed whilst the athlete is in the air the ball will land lower than its projection point, this results in a positive relative height (Blazevich, 2007). The most effective volleyball spikes have a fast downwards trajectory, this gives the opposition less time to react and get themselves in an appropriate position to recover the ball. Highly skilled volleyball athletes were analysed when performing hard volleyball spikes, their representative linear and angular velocity ranges results ranged from fifteen to thirty-five metres per second and had anywhere between three to eight revolutions per second (Kao et al, 1994). If a volleyball is spinning between three to eight revolutions per second it will create a downwards force on the ball causing it to hit the ground closer to its hitting point. Kao et al (1994) describes how a ball with a spin rate of ten revolutions per second can bring the ball up to two metres closer to the net compared to that of a non-spinning ball, as long as all other conditions are fixed. This can make a major difference in games seeing as one half of a volleyball court is only nine metres.

Careful consideration of the Magnus effect and the relation of air resistance can help to ensure successful performance. The Magnus effect refers to the change of trajectory an object has towards the direction of spin. If the angle of the ball is hit steep enough over the net the spike may be unreturnable, in order to optimise the angles and speed of the volleyball the player needs to aim to be as close to the net as possible (Blazevich, 2007). The amount of time the ball is in the air is reduced by using a floppy wrist to cause top spin. This results in the ball experiencing an aerodynamic force known as the Magnus effect, which “pushes” the ball downwards faster (Linnell, Wu, Baudin & Gervais, 2007). Emphasis on specific elements of the volleyball spike allows the athlete to increase the velocity placed on the ball (Abendroth-Smith & Kras, 1999). Often people believe that the follow through is not an important part of the volleyball spike, however this is not the case. The follow through phase is crucial to recovery, injury prevention and transitioning into the next play (Abendorth-Smith & Kras, 1999). Injury and/or poor skill execution can be the result of poorly performed arm follow throughs after ball contact and landings. In order for an athlete to land correctly they must remain balanced by pulling their arms back behind their hips whilst at the same time landing softly with two feet (Abendorth-Smith & Kras, 1999). Trauma related injuries to the landing leg can occur if the athlete lands on only one foot, this is due to greater impact stresses (Mann, 2008).