HLPE3531 Biomechanics Blog
MAJOR QUESTION
What is the most effective technique
for a javelin throw to maximise the range?
Introduction
An in-depth understanding of the biomechanical principles and processes that are evident throughout a javelin throw will assist athletes and coaches in improving their techniques. This will ultimately assist them in achieving their best results, and reaching their goals. The following blog will analyse factors that contribute to the optimal performance technique of a javelin thrower, ultimately aiming to maximise the range of the throw. It will thoroughly examine the components of a javelin throw, such as the run up, release and recovery. Each component of the javelin throw utilizes different biomechanical concepts.
The concepts used throughout this blog include
An in-depth understanding of the biomechanical principles and processes that are evident throughout a javelin throw will assist athletes and coaches in improving their techniques. This will ultimately assist them in achieving their best results, and reaching their goals. The following blog will analyse factors that contribute to the optimal performance technique of a javelin thrower, ultimately aiming to maximise the range of the throw. It will thoroughly examine the components of a javelin throw, such as the run up, release and recovery. Each component of the javelin throw utilizes different biomechanical concepts.
The concepts used throughout this blog include
- Propulsive impulse
- Projection speed
- Centre of gravity
- Angular velocity
- Angle of release
- Kinetic chain (push and throw)
Overall, this blog aims to identify and apply the information and research
developed in regards to executing an effective javelin throw technique. To
answer the major question, ‘What is the most effective technique
for a javelin throw to maximise range?’ The authors will focus on improving the
overall technique of the participant’s javelin throw, whilst also encouraging
specific movement phases.
The variables (thrower and javelin
aerodynamics) that have been selected and measured include the
- Run up speed
- Biomechanical framework of the delivery strides
- Biomechanical variables during the foot strike
- Release speeds, release angle, throw range
- Wind conditions, effects of rotation, different javelin types
- Javelins centre of mass, and the effects it has on the flight distance and landing position
The sport of javelin was introduced
in 1986. However, the javelin has been redesigned many times since. The first
javelin design was altered due to its apparent uncontrollable flight path,
which resulted in a flat landing, rather than a stick landing (Clarkson, 2012).
Having its centre of mass moved forward by 4 cm altered this first javelin. The
tip was also altered in order to make it less aerodynamic (Clarkson. 2012).
Ultimately, these modifications were made in order to allow the athlete to have
some control over the flight path of the javelin, which would therefore
increase accuracy, as the javelin was now able to descend earlier, and in a
downward motion (Clarkson, 2012). This however, resulted in a shorter throwing
distance. This meant that further modification was needed, and these
modifications resulted in the javelin distances increasing. This meant that athletic
stadiums needed to be altered also, to accommodate this distance (Clarkson, 2012).
Figure 1: The original javelin (Clarkson,
2012) Figure 2: The redesigned javelin (Clarkson, 2012)
During the biomechanical analysis
however, the participants did not have access to a traditionally used javelin,
therefore the javelin used during the pre and post-tests was a Turbo javelin. These javelins are
made of polyethylene/plastic material, they are approximately 27 to 44 inches
long, and are very light, as they are generally used for beginners. Therefore,
this was a limitation, and the results may have been different if the correct
equipment was available, in regards to the aerodynamics.
Figure 3: The Turbo Javelin
When considering the biomechanical principles of the javelin throw,
athletes and coaches should also consider the Aerodynamics that can affect the range and accuracy of the
throw. These factors include both wind and gravitation.
Air resistance is generally quite small and can be disregarded when looking at heavy
projectiles over short distances, for example, the shot put (Blazevich, 2012,
p.25). The javelin is a long and light implement.
Women’s Javelin: approximately 2.2m, 600
grams
Men’s Javelin: approximately 2.7m, 800
grams
(Stander, 2006, p.1)
The weight and length can affect the
distance and direction of a throw, therefore, can affect the overall accuracy. Athletes
often throw under very similar or exactly the same conditions during
competition. Therefore, wind is not a large contributor to the final outcome. However,
athletes and coaches should be aware that strong headwinds often require a
decreased angle of release, whereas strong tailwinds require an increased angle
of release (Stander, 2006, p.5).
Gravity affects all objects that have some vertical motion (1-90 degrees).
Gravity can also effect the flight time of an object. Therefore, if an object
is thrown vertically (90 degrees), moving straight in the air, its projection
speed will determine the possible height it will reach before gravity pulls it
back to earth (accelerating at 9.81 m.s-2) (Blazevich, 2012,
p.25).
Run
Up
The athlete begins the javelin throw with a run up. The first biomechanical concept that
is evident during the javelin throw is the Propulsive Impulse. When
referring to Figure 14, it is evident that the participant (Gaby) is using this
biomechanical concept during their run up, as their feet are continuously
moving, therefore creating a propulsive reaction force. A propulsive impulse is
defined as an impulse where the direction of the impulse is the same as the
direction of motion (Contreras, 2013). The
greater the change in momentum means there will be greater change in the impulse.
This is also known as an impulse momentum relationship. Figure 4 below shows
the horizontal ground reaction force. Athletes need to reduce the braking
impulse and increase the propulsive forces. The javelin thrower in their run up
stage exerts a forward force. This forward force elicits a braking reaction
force. When the foot passes under the body, the athlete pushes backwards which
creates a propulsive reaction force (Blazevich, 2012). If the angle between the ground and the foot
is small when placing the foot down, the javelin thrower will gain greater
acceleration in their run up.
Figure 4: Horizontal ground reaction force trace for a runner (Blazevich, 2012)
This follows Newton’s third law ‘for
every action, there is an equal and opposite reaction’ (Blazevich, 2012). This
means that if we apply a force against something that does not move, the object
will exert an equal and opposite reaction force against us. Therefore when we
run the ground is going to exert an equal and opposite reaction force. This
force will accelerate us forward, only if the force is large enough to overcome
our inertia (Blazevich, 2012). Blazevich (2012) states ‘Inertia is the
propensity of an object to resist a change in motion’.
Release
The second stage of the javelin
throw is the release, and this stage includes a range of biomechanical concepts,
as there is a range of movement patterns involved. Firstly, the Centre
of Gravity will be
discussed, as it is the one biomechanical process that has an impact during all
stages of the release. Gravity is the force of attraction between mass or
masses, and is measure in metres per second (Blazevich 2012). An athlete's
centre of gravity whilst throwing a javelin should be near the grip. Kunz and
Kaufmann (1983), state “the better the push forward with the right leg, the
greater the angle between the centre of gravity of the body and the heel of the
left foot which may increase the net power of the javelin at release”. There is
a positive correlation between the javelin throwers who throw between the
optimal angle of release and the centre of gravity of the body (Kunz et al,
1983).
Secondly, the Kinetic Chain
comes into play during the beginning movement. The human body has a moving
chain of body parts, and this is called the kinetic (moving) chain (Blazevich,
2012). There are two main categories of kinetic chain patterns: push-like and
throw-like. Therefore, to begin with, the first biomechanical concept used
during the javelin release is the throw- like movement,
however, the push-like movement will also be discussed in order to
explain the differences, and why they have a fundamental impact on the
movement. As object can be released in two different ways, the push- like
movement pattern consists of moving as if we are pushing something. A push like
movement tends to extend all joints in the kinetic chain simultaneously in one
single movement (Blazevich, 2012). However, a push-like pattern is not used for
the javelin throw. The javelin throw uses a throw- like movement which is different
from the push – like movement as all the joints of the kinetic chain extend
sequentially, one after the other. The figure below can be referred to, in
order to understand this further.
Figure 5: The Kinetic Chain during the javelin throw
A throw-like pattern makes best use
of the human body's tissues and they contain fastening shortening speeds, which
are the tendons (Blazevich, 2012). Elastic potential energy is stored in these
tendons when they are stretched. When that tendon is released, it releases at a
very high speed (high kinetic energy) (Blazevich, 2012). An example of a throw-like pattern in javelin
is seen in the delivery stride within the throwing action. This has the most
proximal segment within the entire action. Newton’s Third Law and the braking
force allows for the transfer of energy, which happens sequentially. From the
shoulder to the most distal point the fingers (Refer to figure 2). The most
fundamental key point to performance in overarm throwing is the sequential motions
that occur from the proximal to distal segments (Blazevich, 2012).
Figure 6: The summation of speed principle illustrated for a throwing example. Each successful distal segment begins accelerating when the contiguous, proximal reaches its maximum (Mechanics research training, 2015)
The
biomechanical principle of leverage is seen in the
javelin throw. A lever is “a rig bar resting on a pivot, used to move a heavy
or firmly fixed load with one end when pressure is applied to the other”
(Oxford Dictionary, 2017). Levers are used to enhance force or velocity. The
javelin throw uses a third class lever where there is force between the fulcrum
and the resistance (Refer to Figure 7).
Figure 7: Third Class Lever (Blazevich, 2012)
Our forearm is classed as a third
class lever, whereby the elbow acts as the fulcrum, which is the point of
rotation for the lever (Blazevich, 2012). Levers have inertia therefore it is
difficult to have rotation. It is seen that athletes usually shorten their
length of levers in their body. Athletes involved in javelin will bend their
arm. It is important that at the point of release to ensure maximum speed, the
athlete straightens their lever (arm), to allow the force to be transferred to
the javelin (Blazevich, 2012). A skill cue that can be used to encourage a
throw like movement and to gain a deeper understanding of it is to throw on the
spot focusing on the throw- like movement and breaking it down.
As the throw has already been
executed, the Projection Speed, or release speed is
the next important biomechanical component. The projection speed is a very
important component of the javelin throw as it can influence the overall
distance that the javelin will travel. Blazevich (2010) states, "If an
object is thrown through the air, the distance it travels before hitting the
ground (the range) will be a function of horizontal velocity and flight
time". Therefore, the projection speed is an outcome of the biomechanical
influences that will be examined throughout the following paragraphs.
Thirdly, the Angular Velocity is
considered. This biomechanical concept occurs during the release, however is
also evident during the run up (refer to figure 14 for visual representation).
Blazevich (2010) defines angular velocity as “the rate of change in angle of
the thrower”. If the thrower is able to increase their angular velocity, they
can then also increase their speed of release. This is done during the release
stage when the athlete is using their torso and throwing arm as a source of
power (Dearmond & Semenick, 1989). During the run up, which is explored in the paragraphs above, the athlete’s (participants) shoulders are relatively
parallel to the throwing section of their body; therefore, they are able to
produce sufficient rotational movement to increase their angular velocity. The
athlete then pulls their preferred arm (in this case, the right arm) backwards;
this movement is used in order to achieve maximum external rotation of the
upper arm during the run up. This creates what is called the power position,
which is when the body is arched, the head faces the
direction of throw, the non dominant leg forward and straight, the dominant leg
is slightly bent, and the chin is in-line, vertically with the right knee and
toes (Stander, 2006, p.4). This is power position creates the maximum
angle, and when reached, it can increase the rate of development for the
thrower (in regards to both range and accuracy).
Figure 8: Example of power position
Figure 9: Gaby’s
post throw power position
The above images show that Gaby’s
power position during the post-test throw still needs modifications. Her
non-dominant arm during the release should be straight (like image 8)
ultimately, pointing to where she wants the javelin to go (flight path). Her
head should also face upwards until release, with her eyes also focusing on the
javelins intended flight path.
Lastly, the Angle of Release is
explored during the final stage, as the participant releases the javelin. The angle of release is when the javelin is released at
ground level, for any given release velocity. Therefore, the angle that
the javelin is thrown can notably influence the distance that it travels. If
the athlete wants to achieve a higher velocity when they release the javelin
(release point), they must use the throw-like movement pattern that has been
mentioned in the above paragraphs. To accomplish a correct technique and
achieve the possible maximal range, the thrower uses the run-up to add momentum
to their throw; this passes through to their arms and also their upper body.
During the release stage of the throw motion, this momentum is shifted to the
proximal portions of the throwing arm. This means that as the momentum is
effectively transferred along the thrower's arm, resulting in a higher velocity
of the javelin. In sequence with transfer of momentum, throwers must also use
elastic energy, to support the increase of velocity.
If the athlete bends their throwing
arm at the first stage of the throw, the tendons are more likely to use
elasticity, therefore the are will react with a throw-like movement, rather
than a push-like movement, at a fast pace. This throw-like movement allows the
use of the simultaneous joints that are evident during this movement to accrue
their force (increasing power) and achieve a higher force overall. The
simultaneous joint rotations will therefore, also result in a straight-line
movement, which means that the javelin throw will have a higher accuracy and
travel distance (Blazevich, 2012).
Figure 10: Angle of Release (Blazevich, 2010, p.26)
The figure above highlights the
angle of 45°. If the javelin is thrown at this angle, it has the more inclined
to travel further. Therefore, throwing at this angle allows the javelin to have
an equal horizontal and vertical velocity (Blazevich, 2010). If the javelin
achieves this maximum range, it will travel further, however, it is stated that
other angles, higher or lower can have a similar increase in range, depending
on the throwers release.
To further assist athletes and
coaches, there is an effective way to measure the linear release velocity. Once
the arms velocity is identified, the release velocity of the javelin needs to
be calculated. To calculate a javelins (or any objects) release speed, there
are two values we need to know:
· The angular velocity of the arm
· The length of the arm
The linear release speed of an object is an objective of the
length of the arm (r) and its angular velocity (ω) (multiply). Therefore we
need to know the..
· Linear velocity is v = rω
· Rotation velocity = 19.7 rad.s
· Arm Length = 0.65cm
Therefore: 0.65 x 19.7 rad.s = 12.8 m.s-1
The athlete release the javelin at 12.8 m.s-1
Figure 11: The release angle. This
figure shows that that for every 3 degrees in difference, there is
approximately a 2m difference in distance (with perfect attack angle) (Clarke,
2014).
Recovery
The final stage in javelin is the
recovery phase. The rule in javelin is that the athlete must make sure their
foot does not go over the line otherwise they are disqualified. In the recovery
phase the left foot must stay grounded whilst the right leg is brought past the
left leg to halt the athlete. The leg is seen to be straight when releasing the
javelin as this increases the speed and the energy is transferred into the
javelin. This can be explained through conservation of momentum, which is
embodied in Newton’s First law (the law of inertia). The momentum of a system
will stay constant if there are no external forces acting on the system
(Blazevich, 2012). The video clip below shows Hamish Peacock an Australian
Javelin athlete. In all of his throws, when he enters into the recovery phase
he has a lot of momentum that he sometimes needs to place his hands on the
ground to prevent him from crossing the line, this is very common among javelin
thrower athletes.
THE ANSWER
(A
case study comparison of approach styles, before and after biomechanical
analysis)
Gaby agreed to undertake a
biomechanical analysis of her javelin throw technique, which we can see in
figure 7 below. Gaby made sure she warmed up her arms and hips before attempting
her first set of three throws. Gaby had three attempts to throw the javelin as
far as possible using her preferred technique.
The results of each throw were recorded. During these attempts it was
evident that Gaby was not leaning her torso slightly forward in her run up.
Leaning the torso forward helps to change Gaby’s motion from rest to vertical
motion. The crossover steps were not evident in these first three attempts. Crossover
steps are important for a javelin thrower to move to a side on position and
maintain their run up speed. When releasing the javelin Gaby did not fully
extend throwing arm on release. If we refer to figure 8, we can see an example
of Kelsey Roberts. Kelsey is a professional female javelin thrower, who has
competed in the Commonwealth Games. Kelsey is used as an example as she is
relatively the same weight and build. When we compare Gaby’s technique to Kelsey’s,
we can see that Kelsey is extending her arm in a straight when releasing the
javelin, whereas Gaby’s arm is bent until the final stage of the release.
Figure 12: Gaby's pre biomechanical analysis of the javelin throw
Figure 13: Kelsey Roberts extends the javelin, which forces her arm to fully extend. Directly before the release of the javelin, the throwing arm has an opposite reaction to the non-throwing arm. During this movement, Kelsey is capable to produce optimal angular momentum before releasing the javelin.
Post biomechanical analysis and upon
discussion with Gaby, she agreed to modify these faults in her technique. She
then has 3 attempts to improve her technique and aimed to throw further than
her previous results. The results were again recorded to compare pre and post-biomechanical
analysis. In the video clip below shows Gaby’s third attempt post biomechanical
analysis and technique correction. Gaby’s
run up included the power position, as her arm was arched during the entire run
up. We can see that Gaby has also attempted the crossover step. She then fully
extends her arm, and releases the javelin with much more force. The table of
results below prove that the increase in distance (range) was likely due to
technique modification.
Figure 14: Post biomechanical analysis and technique correction
Gaby did however show her concern that the change in her technique did feel slightly uncomfortable, therefore, Joanna and Gaby needed to determine if it was worth perusing the technique modifications.
Pre-biomechanical
analysis and intervention
|
Post-biomechanical
analysis, after technique correction
|
||
Throw 1
|
11.7m
|
Throw 1
|
15.5m
|
Throw 2
|
14.5m
|
Throw 2
|
16.6m
|
Throw 3
|
16.4m
|
Throw 3
|
17.4m
|
Average
11.7 + 14.5 + 16.4 = 42.6m 42.6/3 = 14.4m |
14.4m |
Average
15.5 + 16.6 + 17.4 = 49.5m 49.5/3 = 16.5m |
16.5m |
Figure 15: The results from Gaby's throw attempts before and after correction
How
else can we apply this information?
Athletes and coaches, within the
sport of javelin are able to evaluate and transfer the information and results
they discover. The information is similar to that of the bowling run-up during
cricket. This is due to the summation of forces and biomechanics used being
very similar. They are then able to use biomechanics of the skill to be able to
execute the most effective javelin throw. If athletes and coaches are able to
understand the biomechanical principles used within the javelin throw, they
will be able to apply these transferable biomechanical principles to other
skills or sports, and therefore analyse, develop and refine selected sport
skills.
Biomechanical principles are evident
during all fundamental movements. There must be appropriate comprehension of
how each of the biomechanical principles discussed throughout this blog, and
how they can relate to the optimal performance of a skill or movement phase.
This is so that coaches, athletes, and sporting communities can increase
athlete skill ability, which will ultimately increase individual development,
no matter what skill level. Understanding these principles and how we can apply
the appropriate modifications can also decrease the risk of injury during
performance. As these biomechanical principles are evident in many sports
(cricket, tennis, badminton), adopting techniques that focus on outstretching
the arms without hindering technique will assist in achieving optimal
performance. Moment of inertia and the kinetic chain are some of the most
important principles as they have the ability to transfer into other sporting
skills. Athletes should distribute weight in the kinetic chain; loading a
particular part of the body to increase energy for further movement does this.
Therefore, athletes can achieve higher forces, and easily transfer these skills
within other sports. This manipulation of force production can be used for a
sporting benefit throughout a range of sports, such as the back foot motion in
the release and run up stage of the javelin throw, and can also be used through
the beginning phases of the softball swing. It is important to address the
forces associated with weight; for example, to
minimize the effect of inertia and re-distribute an athlete's weight over their
centre of gravity and mass, the athletes can increase the force production at
the point of power production, which is dependent on the skill and sporting
event (Magias, 2016, week7).
Conclusion
Practitioners often rely on a
perceived image of an admired technique to determine whether a change is
required. Gaby’s javelin technique was corrected to suit the ‘textbook model’
of a javelin throw. This approach to technique modification will not always
increase throw development, as it does not target specific individual
athlete/participant characteristics and environmental changes. However, Gaby’s
results (pre and post analysis) show that the throw distance (range) proved
otherwise, as altering the technique increased the distance of each throw.
Conclusively, the biomechanical principles applied within the sporting skill of
the javelin throw can be used and manipulated within other sporting skills for
optimal performance that produces accuracy in timing, power and acceleration.
References
Blazevich, A. J. (2012). Sports biomechanics: the basics: optimising
human performance. A&C Black.
Clarkson,
S. (2012). The Story of the Javelin-
Bringing it Back Down to Earth. Engineering Sport: The Centre for Sports
Engineering Research. Accessed June 5 2017
Contreas, B. (2013), ‘Basic Biomechanics:
Terms and Definitions’. Accessed 15 June 2017,
https://bretcontreras.com/basic-biomechanics-terms-and-definitions/
Dearmond,
R. and Semenick, D. (1989). SPORTS PERFORMANCE SERIES: The javelin throw: a kinesiological
analysis with recommendations for strength and conditioning programming. National Strength & Conditioning
Association Journal, 11(2), p.4.
Kunz, H. Kaufmann, D. (1983),
‘Cinematographical analysis of javelin throwing techniques of decathletes’,
Accessed 5 June 2017,
http://bjsm.bmj.com.ezproxy.flinders.edu.au/content/17/3/200.
Mechanics Research Training, (2015), ‘Momentum
and arm action’, Accessed 6 June 2017, https://www.drivelinebaseball.com/2014/04/momentum-arm-action-myths-misunderstandings/.
Oxford Dictionary, (2017), ‘Lever’,
Accessed 7 June 2017, https://en.oxforddictionaries.com/definition/lever.
Stander.
R. (2006) Javelin Throw, Athletics Omnibus, Boland Athletics, Athletics South
Africa, Houghton. Accessed 15 June 2017, from www.bolandathletics.com/5-13 Javelin Throw.pdf
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