What are some important biomechanics to
consider when performing the optimal javelin throw?
The
Answer:
Step
1:
The run up.
Particular biomechanics need to be
considered in order to perform an optimal javelin throw. Image 1 demonstrates
the position of the athlete’s body during the run up phase. As you can see the
athlete has a high knee lift and the torso is leaning slightly forward. Also,
image 1 shows the non-throwing arm bent at the opposite direction to the
throwing arm (see yellow line in image 1). Naturally, during this phase the
non-throwing arm will be swinging from the front to the back of the body.
Skill
cue 1:
High knee lift, both legs swinging from
front to back.
In order to move the leg backwards (see
blue arrow in image 1), it is important for the athlete to overcome the moment
of inertia (present state of motion). Further to this, Newton’s First Law
(Newton’s Law of Inertia) importantly states that an object will continue to
move at a constant velocity when the net force is equal to zero (Blazevich, 2012). Therefore, swinging
the legs from the front to the back of the body helps the athlete to continue
their speed in the correct direction. Essentially, lifting the knees high
during this phase will also help the athlete overcome the moment of inertia.
Newton’s Third Law also indicates for every action there is an equal and
opposite reaction (Blazevich,
2012). In
this case, the force from a high knee lift is greater when pushing down on the
ground, therefore increasing the ground reaction force. In turn, the ground
delivers an equal and opposite force back on the athlete. This continues
throughout the athlete’s run-up.
Skill
cue 2:
Torso leaning slightly forward:
Newton’s second law states that a force
is required in order to change the object’s state of motion (Blazevich, 2012). Because the athlete
will always begin their run-up from a stationary position, leaning the torso
slightly forward helps to change the athlete’s motion from rest to vertical
motion. As you can see, image 1 demonstrates the athlete’s body leaning forward
close to a 45degree angle from the longitudinal axis (see red line in image 1).
Essentially, this force is pushing the torso forward from the longitudinal axis
and causes the rotation within the legs.
Skill
cue 3:
Non-throwing swings to the front and back
of the body.
This skill cue involves the arm that is
not holding the javelin (see yellow line in image 1). This arm is called the
swing arm and will start from the front of the body and slowly extended from
the shortening position as the legs begin to accelerate. During this phase the
arm will start to swing faster because the mass of the arm is further away from
the shoulder. Therefore, the angular velocity of the arm is greater and will
help to increase the angular momentum of the athlete’s legs (Blazevich, 2012). Also, in order for
the athlete to progress in a linear direction towards the releasing point, the
swinging of the non-throwing arm helps the athlete to maintain balance during
the run-up phase.
Image 1: Body position during
the run up phase.
Step 2: The crossover steps.
The
crossover steps are the steps performed before the athlete enters the
withdrawal position. The crossover steps allow the thrower to move to a side-on
position while maintaining their run up speed. The steps are allowing the
thrower to set up their releasing position while still increasing speed. Image
2 shows the non-throwing arm swinging in front of the body and the throwing arm
is fully extended behind the athlete.
Skill cue 1: Non-throwing
arm in front of the body:
As
the legs are crossing over, the non-throwing arm begins to move across the body
(see red arrow in image 2). Newton’s Third Law states that for every angular
action there is an equal and opposite angular reaction (Blazevich, 2012). In
this case, because the throwing arm is fully extended behind the athlete (see
blue arrow in image 2), the non-throwing arm has moved across and in front of
the body. As the arms swing, another part of the body will tend to rotate in
the opposite direction, this helps to reduce the total angular momentum and
helps the athlete to stay balanced. More importantly, the Law of Conservation
Momentum asserts the total angular momentum of a system remains constant unless
external forces influence the system (Blazevich, 2012). Therefore, when the
athlete is swinging their non-throwing arm in front of their body they are allowing
the total momentum to remain the same (Blazevich, 2012).
Skill cue 2: Throwing
arm fully extended:
Skill
cue 2 looks at the throwing arm and how the javelin is drawn back forcing the
arm to be fully extended. Directly before the release of the javelin, the
athlete’s throwing arm has an opposite reaction to the non-throwing arm. The
yellow arrows in image 2 indicate the upward momentum of the throwing arm and
the downward movement in the non-throwing arm. During this movement the athlete
is capable of producing optimal angular momentum before releasing the javelin,
therefore generating greater force for release (moment of inertia and angular
velocity) (Blazevich, 2012).
Image 2: Body position during the crossover
steps.
Step 3: The withdrawal position.
The
aim of the withdrawal position is to ensure that the movement of the athlete
does not affect the athlete’s momentum. The non-throwing arm begins to swing
away from the body (see red arrow on image 3) and the shoulders and hips are
now in line with the direction of the throw. The shoulders are also now
parallel with the javelin (see white line on image 3) and the angle of release
is roughly at a 45o angle (see blue lines on image 3).
Skill cue 1: Swinging
the non-throwing arm away from the body:
Similar
to skill cue 1 in step 2, with the non-throwing arm swinging in front of the
body, this phase of step 3 discusses the non-throwing arm swinging away from
the body (see red arrow in image 3). As discussed previously, Newton’s Third Law
states that for every action there is an equal and opposite reaction
(Blazevich, 2012). Because this skill cue requires the athlete to swing the
non-throwing arm away from the body, the throwing arm will react by moving in
front of the body. This step is important because when a force is required to
accelerate an object in a particular direction, the athlete needs to produce an
equal or greater force in the opposite direction (Blazevich, 2012).
Skill cue 2: Both
shoulders are parallel with the throwing hand holding the javelin.
Because the athlete
has created a parallel line through the shoulders, from one hand to the other
(see white line on image 3), the muscles acting across the shoulders have
generated a downward force at the throwing hand (Blazevich, 2012). Also, the
downward force of the non-throwing arm has created an upward force in the
throwing arm. Essentially, this demonstrates a weight force that equals zero
and ultimately helps the body to stay balanced.
Skill cue 3: Angle
of release.
The
angle of release is a vital skill cue that requires great thought and practice.
In order to attain the greatest distance, the ideal angle of release for a
javelin throw is between 30o and 40o (Yadav, 2014).
Therefore it is important to discuss the influence of angle projection and how
it influences the projectile range. Because the ideal angle is around 30o-40o
degrees, the javelin has almost an equal magnitude of vertical and horizontal
velocity (45o). Figure 1 provides a good example of the angle of projection
and how the range is affected. Essentially, by throwing the javelin close to 45o
(see blue lines in image 3), the athlete has maximised their throwing range of
the javelin (Figure 1).
Image 3: The withdrawal position.
Figure 1: Angle of projection (Blazevich, 2012).
Step 4: Releasing the javelin.
Releasing
the javelin is the most critical point of the javelin throw. When an athlete
releases the javelin correctly they are ultimately increasing their chances at
achieving their optimal throwing distance. As you can see in image 4, the
athlete’s throwing arm is straight and the non-throwing arm is tucked in. The
athlete in Image 4 is also pushing their body weight forward while releasing
the javelin. Also, there is almost a straight line formed from the back foot
through to the hand releasing the javelin (see red line in image 4).
Skill cue 1: Non-throwing
arm tucked in.
Newton’s
second law of motion asserts that the acceleration of an object is proportional
to the net force acting on it (Blazevich, 2012). In this case, skill cue 1
indicates how the athlete has their non-throwing arm tucked in to the body
(indicated by the blue arrow on image 4). In order to generate power, Newton’s
second law states that acceleration is required to move the javelin (Blazevich,
2012). Therefore, when the athlete is tucking the non-throwing arm close to
their body they are making it easier to generate power because the non-throwing
arm is closer to the primary source of power.
Skill cue 2: Body weight pushing forward.
As
you can see, the athlete in image 4 is leaning forward pushing a lot of their
body towards the direction of the throw. During this skill cue, the moment of force
(torque) is being applied away from the pivot point. The pivot point in this
case is the hips and the athlete is creating torque because the force is being
applied at a distance from the centre of rotation (the hips). Essentially, the
forward rotation of the body is caused by gravity and provides a forward
acceleration helping the body to move faster with less muscle force, therefore
creating more torque (Blazevich, 2012).
Skill cue 3: Straight line from back foot to releasing hand.
While
the athlete is releasing the javelin a throw-like movement pattern is created.
This occurs when the joints of the kinetic chain are extending sequentially,
one after the other (Blazevich, 2012). The red line, seen in image 4, indicates
a straight line that is formed from the toes on the back foot all the way
through to the releasing hand. During this phase, the athlete is using the
acceleration, created from the elbow and wrist, resulting in a high javelin
release velocity. Essentially, by accelerating the proximal segments of the
body and then stopping we are generating a transfer of momentum along the arm
resulting in a higher velocity in the hand releasing the javelin (Blazevich,
2012).
Image 4: Releasing the javelin.
How
else can we use this information?
There
are many sports that involve similar skill cues to the javelin throw. A good
example would be the basic cricket bowling action. Ferdinands,
Marshall and Kersting (2010) state
that the bowling action has a run-up phase that is similar to the javelin
throw. Step 1 has revealed that the run-up phase helps the javelin thrower to
maintain their balance by manipulating their mass of velocities (the arms,
legs, angle of torso). Thus, the run-up phase during a bowling action enables the
athlete to achieve centre of mass velocities that are comparable to the javelin
run-up (Ferdinands et al., 2010). Therefore, the information provided could help cricket
bowlers to improve their run-up technique that will ultimately better the
bowling performance.
Also,
another sport that has similar skill cues to the javelin throw is discus. Dai
et al. (2013) indicated that the
discus throwing performance is associated with kinematic measures such as trunk
tilt angles and ground reaction forces. These measures have been discussed
throughout the javelin throw skill cues and will be influential for improving
the biomechanics of the discus throw.
References:
Blazevich, A. J. (2012). Sports biomechanics: the basics: optimising
human performance. Bloomsbury Publishing.
Dai, B., Leigh, S.,
Li, H., Mercer, V. S., & Yu, B. (2013). The relationships between technique
variability and performance in discus throwing. Journal of sports sciences,
31(2), 219-228.
Ferdinands, R., Marshall, R., &
Kersting, U. (2010). Centre of mass kinematics of fast bowling in cricket. Sports
Biomechanics, 9(3), 139-152.
Yadav, S. (2014). The
Relationship of Selected Biomechanical Variables with the Performance in Javelin
Throw. Journal of Education and Practice, 5(34), 170-173.
Image
1:
The Brown Daily
Herald, (2012). Kinsley ’11 represents U. at Olympics on U.S. javelin team [Image]. Retrieved from http://www.browndailyherald.com/2012/09/21/kinsley-11-represents-u-at-olympics-on-us-javelin-team/
Image
2:
Image
3:
International
Association of Athletics Federations, (2015). Home of world athletics [Image]. Retrieved from http://www.iaaf.org/disciplines/throws/javelin-throw
Image
4:
Dawn News, (2012). Olympics: day 13 [Image]. Retrieved from
http://www.dawn.com/news/741195/olympics-day-13
Figure
1:
Walis, J. (2013, April 26). How can an athlete
maximize the distance of a javelin throw? [Image from web blog post]. Retrieved
from http://biomechanicsjavelin.blogspot.com.au
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