What are the biomechanics of a volleyball spike and how can
we optimise its power and accuracy?
A
volleyball spike is one of the more powerful and aggressive moves in the
popular and competitive game of volleyball. It involves a powerful
downward ‘spike’ motion over a net with the aim of being unreturnable by the
opposition. We as a part of the coaching approach to volleyball are told how to
perform a skill or movement with little reasoning as to why we are performing it
a certain way. The true reasoning behind this is biomechanics.
Biomechanics is the science involved with the study of
forces acting on and within a biological structure and the effects produced by
such forces; the primary purpose of biomechanics is to evaluate the laws and principals of mechanics about human
performance in order to gain greater in-depth understanding and knowledge about
specific details (Blazevich, 2010). It is important to have wide understanding of the applications of physics
into sport and on the human body, as physical principles such as motion,
resistance, momentum and friction play a part in most sports (Delong, 2013).
This blog will
demonstrate the biomechanics behind a volleyball spike and why we need force,
gravity, acceleration, power and accuracy to produce the most optimum spike in
volleyball.
The four key components consist of preparation/take-off,
jumping height, arm swing and the hit. In order to generate the greatest amount
of power when spiking, a volleyball player needs to be able to summate these
forces as one to make them in to one flowing movement.
The biomechanics of these components will now be explained in more
detail.
Preparation
Newton’s First
Law states that “An object will remain at rest or continue to move with
constant velocity as long as the net force equals zero” (Blazevich, 2010). In
relation to this the preparation phase includes a running approach that is
important to give the volleyball player maximum momentum for the height of the
vertical jump in the takeoff phase (Kessel, 2013). Momentum is the product of the mass of the player, and the velocity of
the approach, which in turn relates to the optimal momentum that can be gained
for maximum velocity of height in the jump.
The player exerts
a force bigger than the present inertia, resulting in an increased running
speed on approach to the jump. This leads to Newton’s Second Law which states
“The acceleration of an object is proportional to the net force acting on it
and inversely proportional to the mass of the object” (Blazevich, 2010).
Newton’s Third Law States that “For every action,
there is an equal and opposite reaction” (Blazevich, 2010). The diagram below highlights the forces and
ground reaction forces that are present when the foot contacts the Earth with
horizontal and vertical ground reaction forces evident. The ground reaction forces
can be manipulated to aid in the acceleration if the force generated is large
enough to overcome the inertia (Blazevich, 2010).
It is recommended to plant and take off quickly during an
approach. This is due to the concepts of kinetic energy and potential energy.
During the approach the body has kinetic energy, described as energy in motion,
faster moving objects will have greater kinetic energy (Blazevich, 2010). The
goal is to transfer this kinetic energy into potential energy in
preparation for the jump. If it comes to a stop the kinetic energy will be less,
therefore, preventing jumping as high. Since potential energy is
the product of the mass of the player, gravity, and the height of the jump, the
height is what determines how much potential energy can be attained (Blazevich, 2010).
Jump
To jump a volleyball player requires quick and synchronised
coordination of body movements. The body needs to overcome inertia (Newtons
Frist Law), by having a force applied to the player (Newtons Second Law) by
applying a force against the ground that provides an equal and opposite force
back (Newtons Third Law) (Blazevich, 2010). The power of the jump comes from
the vertical force generated from the foot plant and push-off of the legs using
the major leg muscles. The transfer of momentum is due to the direction of the
foot plant and the use of the arm swing which gives assistance to the height
and direction of the vertical jump prior to take-off (Harrison & Gaffney,
2001). During the 'preparation phase' of
the jump, the player has their knees bent before the full leg extension including
flexion of the foot. Since the sum of forces dictates our acceleration and the
forces of gravity act downwards (Newtons Law’s of gravitation), it is beneficial
for producing large vertical forces and having a lower body mass, in order to jump
very high (Blazevich, 2010).
Figure 2 - Leonell
Marshalls 50 inch vertical jump (Image: fenervoleybol.blogspot.com)
Arm Swing
Hsieh and Heise (2006), found that the arm swing was one of the most important factors which contributed to volleyball spike jump height, one study by MacKenzie, Kortegaard, LeVangie and Barro (2012), found arm swing to increase jump height by 10%27%. In performing the arm swing phase the hitting arm is pulled back with the elbow and hand at shoulder height or higher. The hand is open and relaxed, with the palm facing away from the ear. The elbow then swings forward and is raised above the head. Then the arm and hand swing over the top as the heel of the hand contacts the ball. The summation of these forces travels through the torso to the shoulders, arm and wrist until the force is realised on to the ball. This process assists the arm to store and release the energy from the muscle and tendon at lower extremities, meanwhile helping the trunk to move upward (Hsieh & Heise 2006). The internal rotatory muscles within the arm act concentrically during the arm swing wind up phase, while the external rotatory muscles act eccentrically during the deceleration phase (Dangelmaier & Coward, 2001). Increasing this range of motion for the arm swing allows the arm to generate more energy, which is transferred to various body parts which can improve the overall vertical jump performance (Li-Fang & Gin-Chang 2008). Long levers are another principle in place used to increase an applied force (Blazevich, 2010), whilst short levers are used for fast and accelerating movements. The combination of both long and short levers allows maximum force and acceleration to be applied to the volleyball during the arm swing. The spike combines these two levers; the long lever is made up of the radius and ulna whilst the wrist is the short lever.Hit
Height is a physical trait common in most dominant
volleyball players especially for the spike allowing them to generate more
power when striking the ball (Lynch, 2013). The ball should be contacted
reaching up high with the arm straight, elbow extended, reaching directly above
or slightly in front of the body. The contact point of the ball and hand should
be at the peak of the jump to gain the most power and accuracy (Lithio, 2006), by
using a wrist snapping type motion to direct the ball downward into the
opponents court. Newton’s 3rd law of motion “action and reaction force” and the
conservation of angular momentum are used by the athlete to transfer power to
the ball. Continuing the extension after the ball is released avoids segmental
deceleration which may result in a decreased ball projection velocity and a
slower time of delivery (Shierman & Wehrman, 1998). If the angle of
projection is steep enough over the net the spike may be unreturnable and to
optimise the angle and the speed of the shot the player needs to aim to be as
close to the net as possible. MacKenzie, Kortegaard, LeVangie and Barro (2012), found results to indicate that a higher contact point was associated with an increased volleyball speed, they also came to a conclusion that the speed of the ball after contact was made 24% faster when focusing on achieving a high jump.
More joints used when
making the spike approach means more muscles there to contract and lead to more
force exertion. The kinetic chain allows for the sequential acceleration from
the legs, knees, hips, torso, shoulders, arms, elbows, wrists and fingers, all
possible joints for maximum efforts to contract and produce maximum force and
power to be projected on to the volleyball. The summation of all these
movements can be seen in the picture below resulting in a fluent and effective
action being produced which allows the player to generate greater height, arm
swing and ball contact accuracy and power.
Figure 3 - Volleyball sequence of the spike (Image: www.examplesof.com)
The Magnus effect and air resistance
The airborne time of the volleyball can be reduced by
putting top-spin on the volleyball. This causes the ball to experience an
aerodynamic force known as the Magnus effect, which “pushes” the ball downward
so that it lands faster (Linnell, Wu, Baudin, & Gervais , 2007) it also
reduces the time the opposing team has in deciding how to return the ball. The
figure below illustrates the Magnus effect.
Figure 4 - The Magnus effect. F = Force, V = Velocity. (Image: www.airsoftza.co.za)
As the ball spins, friction between the ball and air causes
the air to react to the direction of spin of the ball. As the ball undergoes
top-spin (shown as clockwise rotation in the figure 2), it causes the velocity
of the air around the top half of the ball to become less than the air velocity
around the bottom half of the ball (Linnell, Wu, Baudin, & Gervais, 2007).
This is due to the tangential velocity of the ball. The top
half turns in the opposite direction to the airflow, and the ball in the bottom
half turns in the same direction as the airflow. This causes a net downward
force (F) to act on the ball. Interesting flight paths can be made with
volleyballs due to the surface of the ball being uneven and a varying surface
roughness from the panels during the flight (Blazevich, 2010). This force is useful for reducing the balls airborne time decreasing reaction time for opposing team.
The Answer
To effectively generate the greatest amount of power when
spiking, a volleyball player needs to perform these components fluently and
summate the forces as one (Lobietti, Coleman, Pizzichillo & Merni, 2010). The
kinetic chain allows for this sequential acceleration of the trunk, torso and
limbs during the spiking action resulting in a fluent and effective action
being produced which allows the player to generate greater jumping height and
optimal contact and power trajectory on ball. The power can be optimised in a
volleyball spike by jumping higher by applying a greater force against the
ground. In doing so the vertical jump gives huge advantage with placement of
the ball especially with the height and angle of projection when taking the
shot. The contact point of the ball and hand was found to provide the power and
accuracy at the peak of the jump, producing the most speed with contact higher on the ball, with the conservation of angular momentum used
by the athlete to transfer the most power on to the ball. The Magnus effect was
also an important factor in producing the most power and accuracy and for
players to know how this factor affects the ball in play. It is evident that
the understanding and mastery of the biomechanical principles can lead to the
efficient and effective spiking technique being delivered. It is the role as
teacher/coach to understand these biomechanical principles to express and apply
these principles to an athlete’s chosen sport to maximise the effectiveness and
efficiency of the chosen skill sequence while minimising the chance of injury
occurring. This leads to our final question of ‘how else can we use this
information’?
How else can we use this information?
This information can be used to improve spike accuracy, and
also learn how to get more power and force into the shot. Having a thorough
understanding of these biomechanical principles not only allows for better
understanding of how to improve results within a volleyball game context but, the principles can also be applied to other sports involving jumping, arm
swinging motions and projection of a ball. Many other sports involve the use of the body
as a projectile. Propelling the centre of gravity to a maximum height can be used
in high jump and basketball jump shots. A high jump has the same biomechanical
principles applied to the movement as the volleyball jump for the spike. The
aim of the high jump is to gain as much height as possible for clearance of the
bar. This requires a large amount of force and power to be able to effectively
and successfully jump over the bar. The basketball jump shot also uses similar
movement patterns, the run up is used to create momentum before changing the
direction of the horizontal inertia to vertical to produce the lift off needed.
The Magnus effect can also be transferred knowledge of skill between sports,
including baseball and cricket on the effect that this has on the swing of the ball. Coaches and athletes can analyse the
biomechanics and ideal conditions that the Magnus effect operates under and apply
it to the sport and ball variations. Beginner volleyball players are often seen
with uncoordinated movements that result in poor spike trajectory and velocity.
On the other hand, professional players will perform the correct movement
sequence to obtain precise summation of forces. Knowing these biomechanical principles
can help teachers, coaches and players to identify errors made by the players
in executing the shot and to correct them.
Understanding biomechanical principles has the capability of
leading to successful execution of a skill and ultimately the production of
athletes who possess greater skills within their chosen sport. It also contributes
to the understanding of the process required to further enhance skills as a
professional athlete.
References
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