What is the optimum projectile angle in maximising the distance of a javelin throw? How can you utilise the kinetic chain in maximising the throw distance of a javelin?

BIOMECHANIC PRINCIPLES:

Projectile Motion

Projectile motion refers to the motion of an object projected at an angle into the air (Blazevich, 2012). The projection speed of an object will impact on the distance it travels (Blazevich, 2012). This is essentially saying that if an object’s projection speed is greater the further the object will travel. The projection angle also impacts on the distance an object will travel (Blazevich, 2012). For example if an object is released at 90 degrees it will return to its release point after gravity has pulled it down. Furthermore, if the same projection speed is applied to an object and the angle is high, the object will attain a higher vertical height then if the object was released at a lower angle but this will then impact the range of the object thrown. The difference in height of projection and the landing level will affect the optimum projection angle needed to obtain maximum range (Blazevich, 2012). In relation to a javelin throw the height of projection is higher than the landing level so therefore the javelin already has some extra flight time. Therefore the optimum maximum range will be achieved by giving a greater horizontal velocity compared to vertical velocity which can be seen in Figure 1 (Blazevich, 2012).

 Figure 1                              SOURCE: Sports Biomechanics: The Basics: Optimising Human Performance, 2012

Kinetic Chain

The javelin throw is much like a throw-like movement as the joints of the kinetic chain extend sequentially, one after the other (Blazevich, 2012). As we know a javelin throw is an overarm action, and Blazevich (2012) explains this action begins with the shoulder extending while the elbow and wrist are flexing during the wind-up phase. The extension velocity of the hands and fingers in the latter part of the throw increases significantly resulting in a high release velocity (Blazevich, 2012). Figure 2 shows the sequential movement pattern from firstly the shoulder to lastly the ball (in this case a javelin). A graph below each stick figure indicates the segment with the highest velocity at that point in time of the action. Note this figure does not include the run up prior to the throw which is the start of the kinetic chain and would also add to the final velocity at the release point. This figure just concentrates on the throwing action. 

 Figure 2                               SOURCE: Sports Biomechanics: The Basics: Optimising Human Performance, 2012
 

What are the mechanics of the throw like pattern?

It has been indicated that transfer of momentum and use of elastic energy probably explain the effectiveness of a throw like pattern (Blazevich, 2012).

Transfer of momentum

The transfer of momentum states that large muscles forces generate momentum in the proximal segments (in this case for a javelin throw; the shoulder) which is then transferred to the distal segments (in this case for a javelin throw; the fingers) (Blazevich, 2012). Due to conservation of momentum, the angular momentum as you slow down the proximal segments of the arm is transferred to the distal segments of the arm and finally in this sequence passed onto the javelin at the release point. Angular Momentum (H) is the product of moment of inertia (I) and angular velocity (w) and therefore if moment of inertia decreases, angular velocity must increase as angular momentum must stay the same (Blazevich, 2012). As we give our arm angular momentum during the throwing action a given angular velocity is produced. However the more distal segments of our arm are lighter compared to the proximal segments of the arm so they have a decreased moment of inertia, and therefore they would have a greater angular velocity for the same angular momentum. This is explained in equation form below as the size of the letter represents the magnitude of the measurement.

             

Proximal Segment

     

         H = Iw                  

the angular momentum is then transferred to the distal segment of the arm where the moment of inertia is smaller and consequently the angular velocity is greater because angular momentum must be conserved.

Distal Segment

  H = Iw

Furthermore, using fictional data can explain how this equation works in act of the throw-like movement and hence show how angular velocity increases from proximal to distal segments while angular momentum is conserved.

Proximal Segment

I = 15      

w = 1

H = Iw 

H = 15 x 1

H = 15

Distal Segment

Due to conservation of momentum 

H = 15

I = 5 (Note: this figure is given as we know distal segments are lighter in mass)

w = ?

Therefore,

H = Iw

15 = 5w

15/5 = w

w = 3

This shows while performing a throw-like movement, angular velocity increases towards the distal segments of an arm. Angular momentum is conserved through both segments, and moment of inertia decreases towards the distal segments. In conclusion, the transfer of momentum states that 'by accelerating proximal segments of our arm and then stopping them, we get a transfer of momentum along the arm that results in a high velocity of the end point (that is the arm)' (Blazevich, 2012).

Elastic Energy

It is said that the throw like movement utilises the tissues that have the fastest shortening speeds which is the tendons (Blazevich, 2012). 'Tendons have mechanical properties which generally make them well suited to act as biological springs' (Shadwick, 1990). When stretched, elastic potential energy is stored in them and when released, this potential energy is converted into kinetic energy resulting in the tendon recoiling at a very high speed (Blazevich, 2012). In relation to the javelin throw, the wrist and fingers is said to contain very long tendons that are capable of storing large amounts of elastic energy. Consequently they allow the propulsion of objects as they are effective at recoiling (Blazevich, 2012). Recoiling of the tendons in the wrist and fingers significantly contribute to the release speed of the implement/object at the end of the throw-like movement. 

Overall, it said by Blazevich (2012) that the effectiveness of the throw-like movement is probably explained by the combination of the two mechanisms; transfer of momentum and use of elastic energy.

 

THE ANSWER:

So what is the optimum projectile angle in maximising the distance of a javelin throw?

To assess how projectile motion impacts the distance of a javelin throw, below is an example with fictional data for angle and velocity. Relative height, time and range are calculated from these which we can then compare other angles to see if range increases or decreases. An elite javelin thrower typically throws a javelin at a velocity of 30m/s (Hubbard, 1984). Also the typical height of release of an average human is 2m (Blazevich, 2012). Hence why Table 1 (NOTE: 11 columns split in two parts) below uses these figures to help show what the optimum angle is to gain the maximum throw distance of a javelin.

Table 1

It is evident from the table that the optimum angle when the release height is 2m and the initial velocity is 30m/s, is 44 degrees. This produced a throw of 93.59m. This is consistent with our explanation of Figure 1 where it shows that when the landing level is below the point of release of an object, the optimum angle is below 45 degrees. Interestingly though the difference in the throw distances is minimal for all angle projections. This is why Table 2 (NOTE: 11 columns split in two parts), below was created to assess the impact of the initial velocity on the throw distance. In table 2 the initial velocity was increased by 1m/s and this increased the average throw distance by approximately 6m. This shows that initial velocity has a greater impact on throw distance than angle of projection. However elite athletes are generally already throwing at their maximum initial velocity and hence why angle of projection is still important in assisting to maximise the throw distance.  

 Table 2

In comparison to the common release angle of elite javelin throwers the findings did not support the optimum angle of projection of 44 degrees. According to Hubbard (1989) this common release angle in javelin is 33 degrees. A possible reason for this is that the more vertically the javelin is thrown the more the athelete is working against gravity to accelerate it (Blazevich, 2012). Hence the initial velocity of the javelin will be less and consequently the throw distance. 


So how can you utilise the kinetic chain in maximising the throw distance of javelin?

To achieve a high velocity at the release point of the javelin, a throw-like movement pattern is necessary. The ideal technique which is shown in the video below is to initiate throwing the javelin by first running, which gives momentum to the body. Once the running phase is over, the momentum is passed to the upper body and arms. Towards the final stage this momentum accelerates the proximal segments of the throwing arm which then decelerates to allow the transfer of momentum along the arm, resulting in a high velocity of the end point. In combination with transfer of momentum, the use of elastic energy is important in increasing the velocity of the throw. As you can see in the video, the tendons in the elbow stretch significantly as the arm bends approximately to 90 degrees (which can be seen at 0.32 seconds) which means there is a substantial recoil thus having a major impact on the speed of the throw. In addition the tendons of wrist and fingers stretch and substantially recoil also contributing to the speed of the throw.

Furthermore, elite athletes have to balance the transfer of momentum and elastic energy from tendons in accordance to their own body to maximise the initial release velocity. This supports the findings from the tables above which indicated that initial velocity has a major impact in increasing the throw distance of a javelin. 

 

HOW ELSE CAN WE USE THIS INFORMATION?:

The calculations used to create both tables above to find the theoretical optimum projection angle can be used for any throw in any sport (e.g. baseball,  cricket, soccer throw-in). By identifying the average initial velocity and release height for a given sport, the same calculations can be used to find the optimum projection angle to achieve maximum throw distance. However the throwing implement and the athlete should undergo separate testing to determine the specific optimum projection angle as the above calculations do not consider these variables and this will give a more accurate and realistic result. So even though these calculations are theoretically based they still show that initial velocity, release height and angle of projection influence the distance thrown. Therefore these calculations can be used as a template in order to investigate the change in factors necessary to achieve maximum throw distance.

We know that the release velocity of the javelin has a major impact on the throw distance rather than the angle of projection. It can be said that the kinetic chain plays a major role in the throw distance as the kinetic chain increases release velocity. This information is important for the coaching aspect of the throw-like movement especially to beginners. This is so as the technique in the throw-like pattern involves transfer of momentum through the body and the use of elastic energy to maximise release velocity. So in terms of coaching, the throw-like movement technique needs to be sound before the angle of projection becomes a significant factor in relation to maximising throw distance.

REFERENCES:

Blazevich, A. (2012). Sports Biomechanics: The Basics - Optimising Human performance. Bedford Square, London: A&C Black Publishers Ltd

Hubbard, M. (1984). Optimal Javelin Trajectories. Journal of Biomechanics, 17: 10, pp. 777-787

Shadwick, R. (1990). Elastic energy storage in tendons: mechanical differences related to function and age. Journal of Applied Physiology, 68:3, pp. 1033-1040

QuinticConsultancy. (2012, February 9). Javelin throw filmed by Quintic - (Slow motion 300fps) [video file]. Retrieved from http://www.youtube.com/watch?v=xlOc6r6E08w