Sunday, April 21, 2013

What are the Biomechanical Principles that underpin the Basketball Jump Shot?

In basketball, the main aim of the game is to pass the ball through the ring to score a goal. This can be achieved in a variety of different shooting forms. These forms include the free throw, lay-up and the jump shot. One of the most common shooting techniques is the jump shot, even though jump shots in competition are difficult because of the small margin for error and the uncertainty of defensive pressure (Knudson, D.V. & Morrison, C. S., 2002). Research has found that the jump shot is distinguished as the most important of all the shooting actions and is the one most often used successfully (Rojst, F.J., Cepero, M., Ona, A. & Gutierrez, M., 2000) (Hay, 1994). Therefore, the biomechanics of this shooting technique will be analysed to determine how to ensure that the end result is a successful goal. 

The Basic Jump Shot Technique
Before an analysis of the biomechanics of the jump shot can be undertaken, the procedure and technique first needs to be understood.

The jump shot technique can be broken down into three very distinct phases. The preparation phase, the execution phase and the follow through phase. Each of these phases plays a crucial role in the likelihood of a successful result.

The Preparation Phase
The preparation phase is the beginning of the shot and is crucial to the execution. In order to begin the shot, the player needs to be balanced. In a typical game scenario, the players will usually be moving forward prior to starting the shot and therefore, the need to be balanced in a dynamic sense (Sport NZ, 2010). The player must also complete this phase with their centre of mass over the base of support (Sport NZ, 2010). The importance of this will be explained when looking at the biomechanics a little later on. To achieve this balance and position of centre of mass, the player should have a staggered stance, the foot on the shooting hand side should be in front of the other. This increases the base of support making the player more stable. Once the player is stable they are ready for the next phase.

The Execution Phase
The execution phase comes next in the jump shot sequence. It is within this phase that the player jumps and shoots the ball. The players aim is to jump vertically only; this is to ensure that upon landing they remain in a balanced position (Sport NZ, 2010). When jumping, the players hips, knees and ankle extensor muscle groups are being used to generate the power to get them off the ground (Sport NZ, 2010). Once the player has reached the maximum height of their jump, they want to release the ball. When shooting the ball, the muscles of the shoulder, elbow and wrist are all initiated at once (Sport NZ, 2010). This then brings the player to the final stage of the shooting sequence.

The Follow Through Phase
The follow through phase is the last phase of the jump shot and it begins with how the player lands from the jump. It is important that the player lands back in a balanced position as this will allow them to prepare immediately for the next action that they need to execute (Sport NZ, 2010). For example, when going in to rebound the ball, for this to be achieved, it is important that they land with a staggered stance and their centre of mass is once again over the base of support (Sport NZ, 2010). The ability of the player to do this greatly depends on what happened in the execution phase. If the player was moving horizontally during the take-off, they may collide with another player upon landing, as this horizontal motion continues until the player has landed (Sport NZ, 2010). The follow through of the arm and wrist is also dependant on the movement of the arm and elbow position during the previous phases (Sport NZ, 2010). However, the player should aim to follow through with their wrist so that they finish with their wrist fully extended and their fingers are pointing towards their foot. The jump shot sequence is now complete.

The Biomechanics of the Jump Shot Technique
The biomechanical principles that will be examined in the jump shot context are projectile motion, Newton’s laws, impulse momentum, centre of mass and ball rotation/spin.

Projectile Motion
Projectile motion refers to the motion of an object projected at an angle into the air, its trajectory is influenced by the projection speed, the projection angle and the relative height of projection (Blazevich, 2010). All of these aspects will be considered to determine when a player should release the ball in a jump shot to increase the rate of success. 

Projection Speed
The distance, both horizontally and vertically, is influenced by its projection speed (Blazevich, 2010). If the projectile moves only vertically, its projection speed will determine the height it reaches before gravity accelerates it back towards the earth (Blazevich, 2010).

In the jump shot there are two projectiles, the ball and the player in the jump motion. The projectile speed of the ball needs to be both horizontally and vertically, whereas, the speed of projection for the player in motion needs to be only moving vertically. When the player shoots, their aim is to release the ball as close as possible to the peak of the jump. This is when there is virtually no forward or upward/downward speed which could affect the players’ judgment of how much force to exert on the ball, as this forward motion would then be transferred onto the ball (Sport NZ, 2010). The vertical velocity of the body contributes to the balls vertical velocity, which can then propel the ball higher than the optimal angle of release (Knudson, 1993).

Projection Angle
The angle of projection is an important factor affecting the projectile range. If an object is projected vertically, it will land back at its starting point. So its range is zero. Objects can be projected at angles between 0  and 90 , where it will travel both vertically and horizontally. A projection angle of  0  means that the object will travel horizontally but not get airborne. If there is a projection angle of 45 , the object will have an equal magnitude of vertical and horizontal velocity and its range will be maximised.

There has been much debate about what the angle of release should be for the jump shot technique. Research has found that it is difficult to pinpoint an exact angle due to factors like court position, height of release, shoulder angle and trunk angle all affecting the angle of release (Brancazio, 1981) (Knudson, 1993).
However, research has found that release angles between 45 -55  will significantly increase the likelihood of a successful goal (Knudson, 1993). See Figure 1. 

“Balls shot with these trajectories have a better chance of passing through the basket than shots with a flatter release angle. Shots closer to the basket or shots from shorter performers will require release angle in the upper range of desirable angles.” (Hudson, 1985)

Figure 1: Illustrates the trajectory path of a basketball released at a 45  angle (Hudson, J.L., 1982)
Relative Height of Projection
The angle that the player releases the ball is greatly determined by the height that the ball is released. An optimized height of release decreases the distance the ball must travel and decreases the ball velocity needed to provide an optimal angle of entry. (Knudson, 1993) Studies have found that if the ball is released at a height below the basket, the angle will have to be greater than 45 , the lower the player is, the greater angle is needed (Sport NZ, 2010).  If a jump shot was to be attempted at midrange to the ring, an angle of 52  would provide the ball with minimum speeds and allow for a clean entry through the ring (Knudson, 1993).
Newton’s Laws
Newtons Laws of Motion are three physical laws that form the basis for classical mechanics. They describe the relationship between the forces action on a body and its motion due to those forces (The American Heritage Dictionary, 2009).
Newton’s First Law
“Newton’s First Law states: An object will remain at rest or continue to move with constant velocity as long as the net force equals zero.” (Blazevich, 2010).
This law is also known as Newtons Law of inertia. All objects with a mass have inertia and the larger the mass, the more difficult it is to change the objects’ state of motion/inertia (Blazevich, 2010).
This applies to the jump in the jump shot technique as well as the movement of the ball. As the player wants to jump off the ground, they must change their inertia to a vertical motion. This law also comes into effect as once the player has left the ground for the jump, they will initially move upwards and only begin to descend when acted on by the force of gravity (Ville, 2011). This also applies to the ball. Once the player has shot the ball, it will continue to move horizontally through the air until the effect of gravity pulls it back down. To be able to change the state of motion of both the player and the ball, Newton’s second law will apply.
Newton’s Second Law
“The Acceleration of an object is proportional to the net force acting on it and inversely proportional to the mass of the object” (Blazevich, 2010).
To change an objects’ state of motion, a force needs to be applied (Blazevich, 2010). This can be applied to the jump shot as the player applies a force on the ball to accelerate it out of the hands, causing the ball to suddenly gain momentum towards the goal. As a result the ball acts back on the player, Newtons third law (Dr Simonetti, J., 1994). However, the player does not take off with an equal speed in the opposite direction due to the player having a greater mass than the ball (Dr Simonetti, J., 1994). Therefore, they will not accelerate backwards (Dr Simonetti, J., 1994).
Newton’s Third Law
“For every action, there is an equal and opposite reaction” (Blazevich, 2010).
This law is closely linked to Newton’s second law. When a force is applied, there is an equal and opposite force applied back. This occurs in the jump shot when the player applies a force onto the ground to begin the jump, the ground then applies an equal and opposite reaction force against the player, causing them to accelerate vertically off the ground (Blazevich, 2010). This law also applies to the force that the player applies to the ball when shooting. When force is applied to the ball, the ball applies an equal and opposite reaction force against the players hands. The ball will then move forward, while the player remains in the same position due to their mass being greater than that of the ball, Newtons second law (Dr Simonetti, J., 1994).
Impulse Momentum
In a game scenario it is likely that the player will be running before they attempt a jump shot. For this reason the impulse momentum should be examined to determine the best possible way the player can transfer their horizontal momentum into the vertical jump and not transfer too much momentum onto the ball.
Impulse momentum refers to the relationship between an objects product of force and time, known as an impulse and the momentum. The greater the impulse, the greater the change in momentum (Blazevich, 2010). An important element of change in impulse momentum is the breaking impulse and the propulsive impulse. The player needs to be able to apply a quick breaking impulse followed by a larger vertical impulse to change the direction that they are travelling (Blazevich, 2010). The player wants to have a shot breaking impulse and spend as little time on the ground as possible before beginning the jump. This is done by ensuring the foot lands further in front of the body’s centre of gravity toe first (Blazevich, 2010).
Centre of Mass
Centre of mass plays an important part in the jump shot technique. Before starting the jump shot, the player must be balanced. This is achieved by having a stable base of support with the centre of mass above the base. When the player applies the force to jump, they want to keep the centre of mass central, so that whole body rotation is not produced, which would cause an unbalanced landing (Sport NZ, 2010). Research has found highly skilled players have less horizontal shift in their centre of mass during the shot (Knudson, 1993). This is because the highly skilled players have the ability to;
“manipulate their body parts, while the centre of mass of the body rises and falls during the jump, according to the law of conservation of momentum. First they bring their legs up under the body, which tends to draw the upper body down relative to the centre of mass, and then rapidly extend their legs to thrust the upper body upwards as the body’s centre of mass falls” (Blazevich, 2010). This creates the ‘hanging’ effect that can be seen in the jump shot technique of experienced basketball players.
Ball Rotation
The spin that a player applies at release is critical in creating a “soft” shot that will rebound into the basket, if it does not pass cleanly through the ring (Knudson, 1993). If a player does not apply any spin on the ball upon release, it may hit the backboard or ring flat. This will cause the ball to spring off in any direction. The spin on the ball will assist it to deflect downwards back into the ring. Research has found that backspin applied to the ball in a jump shot serves to decrease the horizontal velocity of the ball if it strikes the rim, or causes the ball to deflect downwards if it strikes the backboard (Alexander, 1990). It increases the shooter’s margin for error (Alexander, 1990).
There are two techniques that allow players to generate backspin on the ball in a jump shot, the action of the wrist and the angle of the forearm.
Studies have found that “when the ball is held with the correct grip and the forearm is aligned vertically, the shooter can apply pure backspin on the ball. The tendency for shooters to let their elbow drift laterally during the shot takes the arm out of alignment with the basket and causes the ball to spin with a sideward component that may deflect it off the rim.” (Knudson, 1993)
The flection of the wrist is also essential in creating backspin on the ball. The flection of the wrist happens rapidly at the end of the shot upon the release of the ball. Research has found that highly skilled shooters release the ball with their wrist slightly hyper-extended and it stays in this state after the ball has completely left their hands for the follow through (Knudson, 1993). An incomplete follow-through means that the wrist flection is already slowing at release, rather than peaking to create good ball rotation (Knudson, 1993). 
How can we use this Information?
This information can play an important part in teaching the basketball jump shot or correcting players’ techniques. Now that the biomechanical principles that underpin the jump shot are understood, coaches, teachers and players can look at individuals’ techniques and analyse what they might need to change in order to become more successful and efficient.


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