Through out this blog the biomechanics behind a volleyball dig will be explored. How these vary the accuracy of a volleyball dig will be looked at in detail.
Focusing on what angle the ball is hit at when performing the dig affecting the accuracy. The other factor which will be looked into is how the dig is performed. Whether using the whole body or just the movement of the arms makes the shot more accurate.
The
information within this blog is relevant to that of a volleyball dig which is a
quite narrowed down skill as I cannot think of any other sport in which similar
is used.
This
does not mean however, that the biomechanical principles applied to the dig don’t
apply to other sports.
The
angle of incidence can in fact be
applied to racquet/bat sports of tennis, badminton and even cricket where the angle
of which the ball is struck determines where it travels and the accuracy of
each shot. Optimum angles for these sports will differ but the principle of
wanting to be accurate is the same. This biomechanical principle does not just
need to apply to sports but can also be viewed in a light of everyday life. When
writing on paper or other, the angle of which we hold the pen, pencil, texta,
paint brush, ect. determines how thick, thin, faint or heavy the mark is which
is left behind.
The
kinetic chain or summation of force is used when
throwing a ball in any sport or for your dog at the park. It uses the whole body’s
power behind the action to achieve a greater power. In the kinetic chain there
are two types of movement patterns, one of which was covered within this blog,
the push-like pattern, and the throw-like movement pattern. The throw-like movement
pattern has an emphasis on speed behind the object, as would be used for
kicking a football or throwing a netball. The push-like movement pattern is
ideal for accuracy within a skill or task, such as what we want from a volleyball
dig or when playing darts.
When
we are unbalanced it is either because our base
of support is small, for example we are less balanced when standing on one
foot compared to two with them shoulder width apart. Being less balanced is determined
by how easily we are able to be moved or pushed over. Having a solid base of
support is important for everything we do, for example when in the kitchen
using knifes we aren’t likely to stand on one foot as it isn’t as stable as two
therefore unsafe. The centre of gravity
is also important with things we do, as where this is also determines how
balanced we are. This middle point of our mass changes for different tasks, for
example in the rugby scrum the players lower their bodies as to not fall over
from the force which is applied from being pushed and pushing back.
Newton has three laws of gravity and all are
important in what we do, from walking (action and reaction), driving with un-restrained
items and having them hit you in the head when you stop suddenly (inertia) or
trying to lift a heavy box on your own compared with having someone help you (more
mass requires more force).
While
these are the biomechanical aspects I decided to look into in regards to the
volleyball dig, there are many more which have deep principles behind them. Accuracy
of the dig is determined by these biomechanics and for which technique is used
to execute the skill. Having a better understanding behind these biomechanics I
am able to break down the volleyball dig into a more complex skill than what it
appears to be when first performed.
The angle on which the
volleyball is hit on the curvilinear flight down is important.
Now that it has been established what the important
biomechanics are behind the volleyball dig moving on to the answer for
sub-questions can be done. So how does the dig become to have greater or less
accuracy? The angle which the ball is hit also discussed as the angle of incidence is important as if
this is too little or to great the ball will be propelled in an angle which is
not ideal. I took the liberty of getting shots of the ball being hit outside of
my predicted op5timum angle of the ball being hit in. As can be seen in image
3, when the volleyball is hit from approximately 80 degrees to the body, the
ball rebounds off the platform of the arms at a similar angle to which it
travels in prior to contact.
Image 3: A demonstration of when the ball is made contact with at or below 80 degrees to the body that it rebounds in the direction it travelled in the curvilinear path prior to contact.
The image below is when the ball is hit at an angle greater
than approximately 95 degrees to the body and can be seen in the next screen of
the action, the ball travels in a direction which is not ideal. The ball moving
backward means that the team mate of the person who performed the dig is not
able to achieve a set close to the net which is ideal in the volleyball rally (Crossingham,
2008).
Image 4: This sequence of images show that when the ball is hit greater
than approximately 95 degrees to the body the ball will travel a path which is
away from the anterior (front) of the body.
If an angle less than 80 degrees to the body and greater
than 95 degrees doesn’t provide the optimum angle to make contact with the
volleyball in the dig it means that between 80 and 95 degrees is ideal. This can
be viewed in image 1 from the first post of this blog where the player for
Floyd Central’s has lowered her centre of gravity to achieve the ideal angle of
incidence. This image is portrayed with image 5 below where an image of a 180
degree protractor was lined up with the straight of it to her back and shows
that the angle in which the ball was hit is that of 90 degrees.
Image
5: A modification of image 1 showing that the angle which the volleyball was
made connection with is the optimum angle of 90 degrees to the body. Reprinted from VOLLEYBALL: Floyd Central too tough
for Stars in, Hoosier Hills Conference Sports, September 2013. Retrieved 14 June,
2014, from: http://thehhcsports.com/volleyball-floyd-central-too-tough-for-stars-3/.
If the athlete uses
their whole body the accuracy will be greater compared to if just the swing of
the arms is the only motion.
This
theory was a bit more difficult to show as for me to perform the use of leavers
to execute the shot through the use of swinging the arms, my technique had to
be modified. Due to this the kinetic chain technique of the push-like movement
pattern was looked into and captured first.
Push-like movement
pattern of the kinetic chain:
As
discussed in the biomechanical principles behind the volleyball dig, the body
is able to produce more force as the joints of the body are extending at the
same time (Blazevich, 2010). After 10
attempts in doing this style of dig, the ball went into the area which was
marked with a circle 8 of these times. This although is a small scale and with
only one subject to prove the point, shows that this technique is 80% accurate.
Image 6 below shows how this testing was set up.
Image
6: The set up for testing of accuracy using the push-like movement pattern.
Arms as levers for
technique of the volleyball dig:
This
technique used the same set up, the use of a circle of where the ball is wanted
to go to and the same amount of attempts using the shoulders as a pivotal point
for the levers of the arms to make contact with the volleyball in the dig. This
technique proved less accurate as only 50% of the shots (5 out of 10) went in the
circle. Although this may be the case for me personally performing the dig in
this style, someone who is more used to it and it comes naturally to them may
have more accuracy as diversity is a part of sport.
Before the angle of
incidence is gone into detail it must be made aware that when a ball makes
contact with an object (bat, ground, wall or body part) it doesn’t lose energy,
the energy is converted into other forms (Blazevich, 2010). “Coefficient of
restitution
describes the proportion of total energy that remains with the object after
collision (Blazevich, 2010, p. 117)” This energy that remains determines how
high the ball is to bounce after contact, after contact with the forearms the
volleyball will rebound quicker if the platform of the forearms is smoother (Hede, Russell & Weatherby, 2011). The smoother and more
locked the elbows and wrists are the more accurate the ball is at being
performed at the correct angle (Hede et. al., 2011). The angle of reflection is
greater than the angle of incidence which is the flight of the ball when it
comes over the net (Blazevich, 2010). Meaning that for the ball to go in the
air (the dig stopping the ball hitting the ground and preparing for a set)
(Keeling, 2007) the ball must be hit from directly underneath the 90 degree
angle is best as mentioned earlier.
Kinetic Chain – Push-like motion:
Image 2: Visual imagery for kinetic chain of the volleyball dig. Source Unknown
Video 1:
Natalie Schmitting demonstrating a volleyball dig using the push-like motion. (About.com,
2012).
The kinetic chain is also referred to as the summation of forces, which our
body can produce if the joints and next movement from the body is performed at
the right time. This is where the volleyball dig can differ in technique; the ‘correct
technique’ uses a push-like motion which is portrayed in image 2. The figure is
using their legs for the strength, and moving the shoulders at the last bit
just before contact with the ball to achieve the correct angle. This motion
uses all parts of the body to achieve the most power in the dig as can be seen
in video 1 above where Natalie’s body extends at the same time. The other technique is where the arms are used
as levers as their axis of rotation
is that of the shoulders (Blazevich, 2010). This technique only gets power from
that of the rotational point of the shoulders whereas the push-like motion from
Natalie gets power from the proximal joints in her dig.
Centre of Gravity and Base of support:
The centre of gravity is
where the total weight of the body is thought to be concentrated (Encyclopaedia
Britannica, 2014). This is more known as the belly button for most humans as it
is the middle point of our body thus our mass. When setting up for the dig,
Natalie from video 1 gets her body low before the ball has come into view. This
helps her balance and gives her the spring from her legs which produce the
power of the shot. Not only does Natalie get her centre of gravity low to help
balance but as can be seen her feet are at a wide distance apart. This is her
base of support and when this is lower it makes it harder for her to fall over
when performing the shot.
Newton's Laws:
Newton’s first law: This is the law that all things will stay in
motion unless acted upon by an external force. This is also inertia, where the ball
in volleyball will continue to head towards the ground unless it is stopped by
the arms. If this didn’t happen the ball would hit the ground thus scoring a
point for the opposition.
Newton’s second law: Acceleration is dependent on the force and
mass of the ball (The Physics Classroom, n.d.). This acceleration from when the
ball comes off of the forearms is important as it needs to be fast enough that
it goes high enough in the air for the next person to get ready and perform the
set shot.
Newton’s third law: For every action, there is an equal and
opposite reaction (Blazevich, 2010). This law applies to that of the ground
rather than the ball in this instance. When a force is applied to something
which does not move (the ground) an equal and opposite reaction comes off the
ground. In the push-like motion which is used, the ground enables the force to
be equal which is applied to it.
What are the biomechanics underpinning an accurate and effective volleyball dig? The reasoning behind an accurate dig in volleyball is simple, it sets up the team for a powerful attack rather than possibly sending the ball out of court and the opposition receiving a point (Ackerman, 2014). This may be the case but how many different ways are there of performing the task? Most people do it differently to the next although there are different cue points used in these.
The angle on which the volleyball is
hit on the curvilinear flight down is important.
If
the ball is hit on an angle which is less than 80 degrees to the body it is
more likely to propel forward rather than upward (Lenberg, 2007). It works the
same if the ball is hit more than 95 degrees to the body but the ball will be
hit backward rather than up.
Image 1: An example of the volleyball being dug at the correct angle between 80 and 95 degrees to the body. Reprinted from VOLLEYBALL: Floyd Central too tough for Stars in, Hoosier Hills Conference Sports, September 2013. Retrieved 14 June, 2014, from: http://thehhcsports.com/volleyball-floyd-central-too-tough-for-stars-3/.
If
the athlete uses their whole body the accuracy will be greater compared to if
just the swing of the arms is the only motion.
When
the movements from the body are timed right and the body's joints are
progressed at the right time a summation of forces occurs (Coacher
organization, n.d.). This summation of forces increases the power which the
ball is met with as it's push-like motion uses the strength from the whole body, legs, torso and shoulders. This movement pattern can also be referred to as the kinetic chain.
