References

Blazevich, A. J. (2012). Sports biomechanics: The basics optimising human performance (2nd ed.).

                 London: A&C Black Publishers Ltd.

Hirashima, M., Yamane, K. Nakamura. Y., & Ohtsuki, N. (2008). Kinetic chain of overarm throwing

                 in terms of joint rotations revealed by induced acceleration analysis. Journal of 

                 Biomechanics, 41(2), 2874-2883.

Hyysomallis, C. (2001). Balance ability and athletic performance. Sports Medicine, 41(3), 221-232.

Knudson, D. (2007). Fundaments of biomechanics (2nd ed.). California: Springer

                 Science and Business Media.

How else can we use this information?

All of the information provided thus far examines the different aspects of the jump shot. However all this information is practically useless unless a coach can identify and solve a problem with a player's jump throw technique. One approach to analysing technique is using the' five-step method' for bio-mechanical intervention. (Blazevich, 2012, pp.207-210).

We can apply the following steps to a beginner's jump shot in order to identify and improve their shot.

Step 1: Determine the part of the movement that requires improvement. This can simply be done using video footage of the movement as shown below:

Step 2: Conduct biomechanical analysis to determine the flaws in the technique.

Using the knowledge from this blog, we can identify areas that need improvement.Using the above video we can see the following flaws:

• The center of mass is not lowered prior to the jump and therefore there is not enough upward drive which causes a small hop rather than a jump.
• The small jump doesn't allow the player enough time to achieve enough acceleration in the throwing kinetic chain prior to landing. 
• The player starts the throw too early and doesn't have time to correctly aim. Although the camera angle doesn't show, the ball actually flew upwards instead of towards the goals.

Step 3: Testing the athletes personal characteristics.

The player did not perform sufficient stretching and warm up prior to the throw, which  hindered achievement of adequate flexion in the knees, ankles and hips in order to get low prior to jumping.

Step 4: Designing a plan to improve flaws. 

 The following exercises were utilised by the player to improve the motor patterns associated with different aspects of the jump:

• Warm up
• Stretching
• Box Jumps, these taught the athlete to first get their center of mass as low as possible and to drive their knees up as they jump. As it is shown that body weight resistance training improves vertical jump height (Hrysomallis, 2011.)
• Practice steps prior to jump with throwing.

Step 5: Re-testing (After all of the above were performed for 20mins)

Retesting the athlete we can see significant improvements in the technique & although it's not at a professional level jump shot, there is significant improvement.

The Answer (Summary)

Over the previous posts, we have analysed the biomechanics of the handball jump shot. In order to score a goal, both maximal speed and accuracy are required.

To obtain the highest speed, the player follows a open-ended throw-like kinetic chain pattern with sufficient flexion in the hip to maximise the acceleration in all parts of kinetic chain.
Since Force = Mass x Acceleration, by maximising acceleration of the mass(ball), the greatest force occurs when the ball is released at the end of the kinetic chain. Handball players also attempt to eliminate the breaking impulse that occurs when running by throwing in mid air instead of planting their foot down and throwing. 

While in mid flight, handball players are getting closer to the goals, however, they have to throw the ball before their feet touch the ground (within the goal circle) with the greatest possible accuracy.
In order to maximise the duration of time a player's eye level is vertically stationary, the player must manipulate their center of mass by extending their torso at the last moment before the center of mass begins the descend.

How can a handball player manipulate his center of mass to achieve the best accuracy for a goal shot?

As described in the previous post, handball players achieve an advantage of additional speed and distance when jumping into the goal circle. However, in order to achieve maximum visual stability with the goals, the shooter needs to manipulate their center of mass. 


The center of mass is defined as the point (theoretical) where the mass is evenly distributed in all directions. (Blazevich, 2012.) For a male standing up straight, this is generally around the abdomen and may vary depending on physiological factors. In order to maximise hang time in sports such as handball, players use the following center of mass techniques:

Get the center of mass as low as possible prior to the jump- this can be done by lowering the torso. Additional bending of the knees as much as possible also creates a greater distance to exert force on the ground and accelerate, thus creating a better upward momentum. 

The player now drives their center of mass as high as possible by leaving the ground and getting their feet up as high as possible.

 At this stage of the jump the center of mass is now almost at maximum height.

It is important to note that visually (especially in sports like handball and basketball) it may seem like the player is floating sideways (aka. hang time), however the player's center of mass is always in a state of vertical
deceleration/acceleration due to Newton's 2nd law and its application to gravity. As we will find out in the next phase, it is only the top half of our body that 'hangs' in the air.

The final phase of the movement occurs just before the player's center of mass starts to accelerate downwards. Being the highest point in the maneuver, the player extends their hand and throws the ball while driving their legs downwards.

As the legs are extended downwards, there is a conservation of momentum and the upper body moves upwards. Since the overall center of mass starts moving downwards, while the upper body is relatively moving upwards, it gives the 'hang' effect to the upper body (Blazevich, 2012.) This split-second allows a well conditioned handball shooter to have improved aim since their head and eyes are at the same level for a moment longer. 


Additionally, handball players have to maneuver and shoot around multiple defenders. In order to do this successfully without loosing balance, they also need to manipulate their center of mass. For example in the instructional video below by Salming Handball, the shooter leans in to perform a 'feint' shot by tricking the defender into thinking he will shoot then twisting around his center of mass to evade the defender.
Notice that the defender also moved his center of mass towards where he initially believed that the ball will go, however, did not have sufficient time to go against his momentum and turn the other way.

How does the jump affect the speed and accuracy of the ball? - Part 2 : Jumping up and over a defender.

When a defender is blocking the shooter, unless the player chooses to pass, the only option is to shoot over the defender. In such a scenario, the shooter doesn't aim to jump forward into the goal square but rather to jump as high as possible and shoot over the defender. This allows the player to visually see where he or she is shooting and it also gives the ball more time to accelerate downwards. This is due to the increased release height, which creates more distance for acceleration due to gravity (about 9.8m/s).(Blazevich, 2012). This can be used strategically to cause the ball to have a greater bounce for goal.

 

Below is a instructional video, shot by Videojug, on how to perform the jump . Notice that when possible, all players still attempt to jump forward into the defender in order to minimise momentum loss as per part 1. 

How does the jump affect the speed and accuracy of the ball? - Part 1 : Jumping Into the goal square.

In this section of the blog we will consider the bio-mechanical benefits of a player jumping at roughly 45 degrees into the circle and throwing the ball at the goals mid-air. The primary benefit of this is that the player is physically closer to the goals, thus giving the goal keeper less time to react to the shot.

As demonstrated above, this shot is only physically possible if there are no defenders in front of the shooter.

This type of shot also increases  the velocity of the ball by allowing handball players to maintain momentum by jumping forwards into the goal circle after running, instead of planting their foot down and stopping prior to throwing the ball.

In order to analyse how jumping  assists in adding speed to the throw, we first need to understand the concept of impulse. Impulse is described as the effect of force acting over time (Knudson, 2007.) When running,  there is breaking impulse when the foot initially lands and then a propulsion impulse when the foot pushes off the ground after landing.  The key difference between breaking impulse and propulsion impulse is the direction of force.

The picture above demonstrates the direction of force. Since the foot is applying force onto the ground, the ground is applying equal but opposite force to the foot according to Newton's third law: every action has an equal but opposite reaction. The direction of force is against the motion of the body and therefore, the body slows down.

In contrast to the breaking impulse, the propulsion impulse lasts longer and the vectors of force create a forward force which allow for increased velocity of the body.


In sports such as cricket, the bowler has to put their foot down before the crease, thus creating a equal but opposite force and reducing the momentum body (including the ball).












However, in handball, players are allowed to jump and throw the ball within the circle, as long as their foot is not within the circle when they let go of the ball. This essentially means there is no breaking impulse in mid-air (neglecting air resistance) and the players can throw at a higher speed than if their foot was planted on the ground.

How can a player exert maximal force on a ball as to increase is velocity.

Since the objective of handball is to score points by throwing the ball in the goals from at least 6 meters out, the players require efficient throw-like kinetic chains. The throw kinetic chain is characterised by the joints in the kinetic chain, which extend sequentially (Blazevich, 2012.) However, that is not to say that there is no overlap in the sequence. For example, while the wrist and knuckle are the final accelerants prior to release of the ball, the shoulder is still accelerating during release (Hirashima, Yamane, Nakamura & Ohtsuki, 2008.) The order of major acceleration in the handball throw kinetic chain is as follows:

Shoulder > Elbow > Wrist > Knuckles > Ball (open end)

For a handball throw, the kinetic chain is open-ended, meaning one end of the kinetic chain is free to move (the ball).  By accelerating each of the segments of the kinetic chain, the momentum is transferred along the arm to the end point (Blazevich, 2012.) and since we have an open-ended chain, as described above, all the acceleration is transferred into the ball, causing a high force to be applied on the ball throughout and at the end of the kinetic chain. This can be described using Isaac Newton's second law in mathematical terms:

 Force= Mass (Ball) X Acceleration (achieved through various stages of the throw like kinetic chain)
 

Although not mentioned in the kinetic chain above, hip rotation plays an important part in creating additional force in the kinetic chain and does so in a couple of ways. Firstly, it makes the arm a longer leaver, thus allowing more distance for the kinetic chain described to accelerate and apply more force to the mass (ball).

This is demonstrated below using two figures. The first shows how far back the ball is with no hip flexion and the second demonstrates how far back the shoulder can move with significant hip flexion.

The second way the hip can create additional acceleration is by simply twisting back in place. This actually applies to all of the tendons attached to the joints described above, at the end of the first paragraph.  When tendons are stretched, they build up potential elastic energy which then recoils at high speed (Blazevich, 2012), thus producing additional acceleration during the chain.