The two most important and controllable factors for a successful trajectory are within the javelin release speed and release angle. The release speed is essentially controlled by momentum developed over the run-up; therefore, a javelin throw is not successfully possible without one. We know that athlete’s acceleration progresses when at the early stages of running; however, it is how this speed is progressed and maintained through the crossover phase which really influences trajectory. "Javelin throwing is technically demanding" (Liu, Leigh and Yu, 2010) which is why each section of the skill needs to be technically correct. With regards to the below figure, this blog will have a focus on the approach and the 5-step rhythm which is outlined.

Initial stage of the run-up

A javelin throw involves a run-up aiming to build up as much momentum as possible before transferring into the crossover phase. The torque created by the horizontal ground reaction force causes a forward rotation of the body and the propulsive impulse acts as a force applied to move forward and accelerate. Both these principles are essential in a quick acceleration for the run-up. Below describes the movements and positions of the run-up for a right-handed thrower and how they work to assist javelin trajectory.

The position of the body when running

The body is running in a forward linear motion during the initial run-up phase. At the start of the run-up, the javelin is carried above the shoulder with the arm bent at the elbow and the hand holding the javelin at head height to maintain control and stability. As seen in figure 2, the back needs to be in a straight proportion to help keep the javelin horizontal which acts to smoothly slice through the air, gradually developing to angle the javelin at the angle of release in further phases. Eyes also need to be focused ahead to improve the accuracy of movements.

Figure 2

How the arm positions assist in movement during running

The left arm is moving in an angular motion during this initial running phase. The faster the arm swings the more angular momentum it possesses, therefore, the more opposing momentum is induced in the body. At the same time, the right hand holding the javelin is acting in a ‘bobbing’ action held aside the head. The javelin is held close to the center which helps the body maintain center of mass, vital for control. Correct arm swing plays a significant part in conserving angular momentum in the runner which assists the body in preparing for the further phases when the release of power is required.

How the correct leg movement enhances momentum

The aim for the run-up is to maximize angular momentum of the leg which will facilitates optimal speed. Angular momentum is greater when the joint torque is produced over a longer period of time, therefore, the athlete should have a slight bend of the knee to maintain speed; however, in the swing phase of the run, the legs need to be relatively straight when landing on the ground to make sure linear velocity of the foot is at its greatest due to being further away from the hip. Another example of maximizing angular velocity in running includes having longer stride lengths and extending the height of the knee during steps. Runners are able to move forward due to the backward force which is applied to the ground, therefore, contact time between foot and ground will act to push the body forward.

Final stage of the run-up: The crossover

This phase is built on maintaining the momentum gained from the initial run-up. The aim of the transition phase, also known as the impulse-step or crossover, is to place the right foot ahead of the athlete's center of gravity to produce the characteristic to lean back so the power accumulated is already positioned close to the throwing arm. Within this phase, the athlete is preparing for the pre-delivery position, aiming to achieve it without a loss of the speed accumulated. Below are the skill queues described which are involved with the crossover.

Position of the body prior the crossover

Following the run-up, the athlete starts preparing for the crossover by altering the body position into a sideways direction with the left hip moving to face the frontal direction of the throw. Having the athlete face the side allows the chance to achieve a greater range of motion for a good release position and assists the body in maintaining momentum and stability through the crossover. The throwing arm with the javelin moves behind the athlete's center of gravity so it remains in a stationary optimal position throughout the final run-up stage, ready for release position. 

The position of both arms during the crossover

The arms are fully extended and move to a 45°angle linear with the javelin’s direction to assist in accuracy and the centering of mass. Having the arms extended also prepares for the equal and opposite reaction of a 'push/pull' action to take place following the crossover and into the trajectory. This position indicates a slight misalignment of center of mass and center of gravity although still acting to help the body remain stable into the proceeding motion whilst maintaining optimal speed.

the position of the legs and feet during leg cross-over

Figure 3 (Clark, 2014)

As figure 3 demonstrates, this movement should be active and low to ensure that the body's center of gravity is not disturbed and that momentum from the run-up is smoothly carried over into the arm, without any loss of speed. After the first step, the right leg is in front which enforces the kinetic chain of the left leg to follow forward to maintain center of mass and stability, resulting in advancing ahead of the vertical axis ready to be in place for a speedy plant after the right foot has landed. The second to last crossover step is slightly exaggerated to allow the thrower to land with their weight over their back foot which will enable the thrower to attain an optimal power position. As the right foot plants, the thrower’s hips should begin twisting forward, creating angular momentum. This motion acts to maintain momentum whilst preparing the trajectory of the javelin with the power being developed on the throwing side. Figure 4 indicates how figure 3 transfers into a real circumstance.

Figure 4

How the body reacts following the crossover: the transfer

Following the crossover, the athlete's center of gravity should be above or slightly behind the right leg with the body aligned in a 115° angle; this sets up the body to apply momentum when changing to the opposite direction during the last delivery step. The delivery step allows the thrower to transfer the momentum built from the run up into the javelin. The javelin is also angled in a 45° angle in preparation for accurate projectile motion with the arms fully extended ready to generate power from the torque. Angular impulses from the forces exerted by the ground on the athlete’s feet prior to trajectory helps generate angular momentum for the combined power and accuracy needed. This final stage of momentum transfer into the javelin is achieved in a movement that travels from the center of the throwers body to the end of the athletes throwing hand. It is a whip-like transfer of energy from the hip to shoulder to elbow to javelin. 

It is important the thrower reaches a high velocity to build significant momentum to be transferred into the thrower’s arm for a 45° release. This optimal angle for throwing a javelin gives equal vertical and horizontal velocity to give the maximum range (Blazevich, 2010). Maximum release speed implies acceleration, which in turn implies force created by powerful muscular contraction, but where does the force come from? Blazevich (2010) explains, when running, the ground exerts an equal and opposite reaction force which is applied both vertically and horizontally, as demonstrated in figure 5. This equal and opposite reaction acts to accelerate the runner forward if the force is large enough to overcome inertia. This is an example of Newton's third law in action stating, ‘for every action there is an equal and opposite reaction’ (Blazevich, 2010).

The closest correlation to javelin performance is in the maximal anaerobic power of the legs (Bouhlel, Chelly, Tabka & Shephard, 2007) which emphasizes the importance of the leg muscles and movements in this sport. The athlete is landing on the ball of the feet to exert angular momentum. If the athlete was landing on the heal of their foot, a force would be exerted which elicits a backward or braking reaction force (Blazevich, 2010). If correct form was followed and high acceleration was reached, the inertia of the thrower will continue to pull the athlete forward after the release of the javelin.

Figure 5

The answer:

We know that the release speed has the greatest influence on the distance the javelin will travel. Although how would the crossover run-up differ from a linear run-up? The answer is in the way the crossover technique allows the body to alter into a side on position whilst maintaining great momentum following the initial stage of the run-up. A solo linear run-up may allow for faster acceleration, although will lack in transferring gained momentum into a powerful trajectory, which is a reason as to why velocity in a straight line doesn’t really exist in sport. The body would simply not be able to transition smoothly from the run-up phase into the side on position for release, which is vital for the javelin throw.

By using the right biomechanical principles implemented during the run-up of Newton’s Laws, conserving angular momentum, utilising torque and center of mass, overcoming inertia, impulse-momentum, acceleration, and velocity, the trajectory of the javelin will consist of a forceful delivery into positive acceleration which will then reflect on the javelin’s moment of inertia turn and negative acceleration to be at greater distances. All these discussed biomechanical principles should be applied during initial and final stages of the run-up to allow for maximum momentum to be transferred into trajectory. However, if the thrower is unable to attain a good power position, these principles will not be applied successfully. The legs, strong core muscles and firm upper body provide a stable support for a maximum release velocity and therefore, should be a focus for strength training.

     

How else can we use this information?

This information on the run-up can be analysed and transferable to any sports that also involve velocity to gain momentum for release. The bowling action in cricket is a comparable skill which also needs the similar biomechanical principles applied to obtain the most effective and efficient throw. Through understanding the biomechanical principles of the javelin run-up, coaches, athletes and physical education teachers can apply these transferable biomechanical principles to other skills and sports. Coaches and athletes should strive to develop the ability to generate maximal power in the shortest time possible which has to be achieved at higher movement speed, therefore speed and strength training will be most beneficial. Wuest and Fisette (2012) explain how understanding the factors that govern human movement and the forces involved in producing athletic movements is essential for all physical education, exercise science and sport professionals. 

Below indicates an accurate slow motion run-up from the side and back of the athlete with all the skill queues implemented. This is also a great indication to see how angular momentum is being developed in the left arm during running.

(Iversen, 2014)

Reference list:

Barber, M. (2014). Science in the spear: biomechanics of a javelin throw. [online] Available at http://theconversation.com/science-of-the-spear-biomechanics-of-a-javelin-throw-29782 [Accessed 16 June 2015]

Blazevich, A. (2010). Sports biomechanics, the basics: Optimising human performance. A&C Black

Bouhlel, E., Chelly, M. S., Tabka, Z., & Shephard, R. (2007). Relationships between maximal anaerobic power of the arms and legs and javelin performance. Journal of Sports Medicine and Physical Fitness, 47(2), 141-6.

Clark, J. (2014). The Penultimate Step: Fly or Fail. The Jav Lab. [online] Available at: http://www.just-fly-sports.com/the-penultimate-step/ [Accessed on 16 June 2015]

Iversen, M. (2014). Javelin Throw Slow Motion. Youtube [online video]. Available at https://www.youtube.com/watch?v=GTBVJMCWj5Q

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.

Stander. R. (2006) Javelin Throw, Athletics Omnibus, Boland Athletics, Athletics South Africa, Houghton [online]. Available at www.bolandathletics.com/5-13 Javelin Throw.pdf 17/6/2015 [Accessed on 17 June 2015]

Wuest, D., Fisette, J. (2012) Physical Education, Exercise Science, and sport (17^th Ed). New York, NY; The McGraw-Hill Companies, p.113.