Does throwing a Javelin
biomechanically correct increase the throwing distance?
The javelin
throw is one of four throwing events in track and field. It has a run up which
consists of a serious of cross steps; the delivery which relies on speed,
direction and height and the recovery which decreases the momentum preventing
disqualification. "Javelin throwing is technically demanding" (Liu, Leigh and Yu, 2010, p. 1459) which is why each section of the
skill needs to be technically correct.
Figure 1 (Livestrong.
2013).
Looking at
biomechanical principles in relation to the javelin throw will focus on
improving technique and encouraging specific movement phases. Rules of the
sport impact the throw and will impact how the biomechanical aspects can be
formed.
Run up-
Propulsive
Impulse
Propulsive
Impulse is the force that is applied to move forward and accelerate.
While
performing the run up the javelin is
moving with you at the speed of your run. When
you then apply extra force through adding muscles the force to
accelerate increases. Therefore the faster the run up the further the javelin
should go. However this is not always the case
because as you add speed the technical approach to the throw becomes increasingly
difficult. To increase the speed of the run up a skill cue could be given
around foot placement while running.
If the
athlete is landing on the heal of their foot a force is being exerted which
"elicits a backward or braking reaction force. Since the force is applied
over time, the area under the curve is the braking impulse" (Blazevich,
2010, p. 55). When the
foot lands under the body it creates a propulsive reaction force which will
increase the speed when running. The smaller the angle between the foot and the
ground when you are placing your foot the greater the acceleration gained. This
decreases the braking impulse which is a product of applied forces and the time
over which it is applied which will slow the running speed.
Figure 2 (Blazevich, 2010, p. 55).
Every force has an equal and opposite reaction- Ground
reaction force
When running the "ground exerts an equal and opposite reaction force" (Blazevich, 2010, p. 45) a force is applied both vertical and horizontal which exerts an equal and opposite reaction. This "accelerates us forward if the force is large enough to overcome our inertia" (Blazevich, 2010, p. 45).
When running the "ground exerts an equal and opposite reaction force" (Blazevich, 2010, p. 45) a force is applied both vertical and horizontal which exerts an equal and opposite reaction. This "accelerates us forward if the force is large enough to overcome our inertia" (Blazevich, 2010, p. 45).
A skill cue that could be provided to the athlete to increase their performance
of the run up could be to decrease the time that the foot is on the ground. In
order to run faster, stance to must be shorter. However when stance time is
shorter there is less time to produce an impulse, so the peak force must be
higher.
Figure 3 (Tongen, A. and
Wunderlich, R., N.D).
Figure 3 shows that the vertical ground reaction force is much high and
over a much shorter time while running than walking. This increases the speed
through using Newtons 3rd law every force has an equal and opposite reaction.
Release-
The second
phase of the javelin throw is the release. The release is very technical and involves
all body parts.
In preparation
to throwing the javelin the athlete should move the javelin to the rear of
their right shoulder keeping the arm straight and the palm facing upwards. Accelerate
forward while rotating the shoulders to line up with the direction of the throw
with the hips remaining forward to maintain approach speed (Stander, 2006). The
tip of the javelin should be close to the athlete's head with the point at eye
level.
To prepare
for the throw the trunk leans back to maximise the pull of the throwing arm.
The dominate foot should touch the ground first slightly in front of the hips
and shoulders. The dominate arm still fully stretched while bringing the non
dominate leg forward and transferring the weight through the hips.
Projection speed
The release speed has the greatest influence on the distance the javelin will travel. "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" (Blazevich, 2010, p. 25).
Push/Throw
There are two ways that an object can be released or moved. There is through a push which movement which "tend to extend all joints in our kinetic chain simultaneously in a single movement" (Blazevich, 2010, p. 196). The push movement in generally done in movements such as a leg press or squat lift exercises. When throwing a javelin the "joints of the kinetic chain extend sequentially" (Blazevich, 2010, p. 198). This makes the javelin a throw movement rather than a push.
There are many technical aspects of javelin which can make it difficult to execute correctly. To encourage the athletes to use a throw movement do an experiment with them to increase understanding. Just standing on the spot get them to release the javelin using a push movement. As they are not moving they will not have all the other sequences to think about as well. Once they have done this throw measure it then repeat using a throwing motion. There distance should increase, however they may understand this, they may just find it difficult when performing the movement as a whole. To overcome this pedagogical implication the skill could be broken down and taught in sequential steps.
Centre of gravity
Your centre of gravity while throwing a javelin should be near the grip, this does not change throughout the different stages of the throw. "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"(Kunz and Kaufmann, 1983, p.203). Research states that there is a positive correlation between the velocity of the centre of gravity of the body and the throwers who throw between the optimal angle of release (Kunz et al, 1983). When teaching javelin a skill cue to encourage the correct centre of gravity being obtained could be to encourage core strength . Increased core strength will increase hip movement and increase flexibility in the back and shoulders.
Angular Velocity
"Angular velocity is the rate of angular displacement"(HyperPhysics, 2000). The angle the javelin is thrown will greatly impact the distance it travels.
Figure 6 (Blazevich, 2010, p. 26).
Figure 6 shows that if a javelin is thrown
at 90° and 0° it will have a range of zero.
The optimal angle for throwing a javelin is 45°, this
has equal vertical and horizontal velocity and will give the maximum range (Blazevich, 2010). Generally a
javelin is thrown at an angle between 30° and 36°, "the faster the javelin
is thrown, the lower the trajectory will be" (Stander, 2006). Angle is something
that will be impacted on through the way the javelin is being help throughout
the run up, and the trunk position in the throwing motion. This may be hard for
athletes to change once they have done it this way for awhile. It is best if
this is taught from the beginning, however it can be changed through teaching
each phase sequentially.
Figure 7 (Mackenzie, 2014)
Recovery-
The final
stage of the javelin throw in the recovery phase. "The left foot remains
grounded and the right leg is brought past it to halt the athlete. The amount
of space needed to stop before the scratch line depends on the amount of
horizontal momentum" (Healthy
Living, N.D). Stoping
before the line is critical, if the athlete's foot goes over the line
elimination will occur.
The above
clip shows that many professional javelin throwers fall after their throw or
they put their hand on the group to help gain control. This is because they
have so much forward momentum.
The straight leg that is talked about in the above YouTube
clip is similar to the release movement that is done in javelin. The clip
states that 5 times the body weight is going through that leg as the high
amount of forward momentum is being produced. Having the leg straight increases
the release speed and more energy is transferred into the throw. However having
the leg straight increase the chance of injury significantly and should not be
done.
Equipment
The javelin's
design has changed throughout the sport. The original javelin "had the
centre of mass at the centre of pressure" (Engineering Sport: The Centre for Sports Engineering
Research, 2012). These
means that the javelin can be lifted through the air if it is angled
appropriately. "As the centre of mass and centre of pressure
coincided the pitching moment (how the javelin rotated during flight)
completely depended on the way it was thrown" (Engineering Sport: The Centre for Sports Engineering
Research, 2012). The flight path of these javelins were very
uncontrolled and the nose could point either up or down in flight. Also the
javelin would fall out of the sky often landing flat which resulted in a no throw. (Engineering Sport: The Centre for Sports Engineering
Research, 2012).
Figure 8 (Engineering Sport: The Centre for Sports
Engineering Research, 2012)
The
redesigned javelin was introduced in 1986, the centre of mass was moved forward
by 40mm from where it was at the centre of pressure (Engineering Sport: The Centre for Sports Engineering
Research, 2012). The tip
of the javelin was also altered with it now being blunter and less aerodynamic (Engineering Sport: The Centre for Sports
Engineering Research, 2012). These
modifications meant that there was reduction to "the lift on the
javelin, bringing down the nose of the javelin and meaning that it will stop
climbing and start to descend" (Engineering
Sport: The Centre for Sports Engineering Research, 2012). The point in
which the nose begins to descend will happen earlier than the old javelin
design meaning it will begin to descend earlier resulting in a shorter distance
being thrown.
Figure 9 (Engineering Sport: The Centre for Sports
Engineering Research, 2012)
Conclusion
Throwing the
javelin biomechanically correct does increase the throwing distance. This is
shown through looking into each biomechanical aspect and seeing how this
correlates with the javelin throw. There are many skill cues that can be given
to the athlete to improve their throwing technique. These will provide feedback
without confusing them with the biomechanical terms and explanations. Each
phase of throwing the javelin requires biomechanical principles to obtain
maximum distance. Propulsive impulse is required through the force that is applied.
Equal and Opposite reaction is a part of the running style, projection speed
impacts the distance of travel, the throw technique using the joints of the
kinetic chain extend sequentially, centre of gravity for balance and angular velocity
to increase distance.
Applying
biomechanical knowledge to increase the javelin throw will be transferable
between other athletic events. The principles will stay the same for other throwing
events with the optimum angle always being less that 45° as this has equal vertical
and horizontal velocity and will give the maximum range (Blazevich, 2010). Using skill
cues and catering for individual throwers will encourage changes to technique
of the thrower.
Reference List
Blazevich, A. (2010). Sports biomechanics, the basics: Optimising human performance.
A&C Black
Engineering
Sport: The Centre for Sports Engineering Research, (2012). The Story of the
Javelin- Bringing it Back Down to Earth. [online] Available at: http://engineeringsport.co.uk/2012/09/21/the-story-of-the-javelin-bringing-it-back-down-to-earth/
[Accessed 16 Jun. 2014].
Healthy
Living, (N.D). Stages of the javelin throw. [online] azcentral.
Available at: http://www.lavic.com.au/Portals/43/Documents/Coaching%20Handouts/Javelin1.pdf
[Accessed 16 Jun. 2014].
Kunz, H.
and Kaufmann, D. (1983). Cinematographical analysis of javelin throwing
technique of decathletes. Brit. J. Sports Med, 17(3), pp.200-204.
Linthorne. N. (2013) Optimum Angles of Projection in Throws and
Jumps, CoachesInfo.com, University of Sydney, Australia
Liu, H.,
Leigh, S. and Yu, B. (2010). Sequences of upper and lower extremity motions in
javelin throwing. Journal of Sport Science, 28(13), pp.1459-1467.
Livestrong. (2013).
Physics of Javelin Throwing | LIVESTRONG.COM. [Accessed
13 June.2014], from
http://www.livestrong.com/article/431055-physics-of-javelin-throwing/
Mackenzie,
B. (2014). Javelin. [online] Brianmac.co.uk. Available at:
http://www.brianmac.co.uk/javelin/ [Accessed 16 Jun. 2014].
Stander. R. (2006) Javelin Throw, Athletics Omnibus,
Boland Athletics, Athletics South Africa, Houghton www.bolandathletics.com/5-13 Javelin
Throw.pdf (cited 13/6/2014)
Tongen, A.
and Wunderlich, R. (N.D). Biomechanics of Running and Walking. [online]
Available at:
http://www.mathaware.org/mam/2010/essays/TongenWunderlichRunWalk.pdf [Accessed
13 Jun. 2014].