Tuesday, 23 April 2013

Biomechanics in Basketball


“What are the biomechanics behind an accurate jump-shot?”


Introduction

The common basketball shot has developed over the decades. Over the years biomechanics have become a large part of basketball and the way a basketball player shoots the ball. The jump shot has become one of the most common shots used in basketball. The jump shot helps a player elevate their body above their opponent, this makes it harder to defend and helps to give power to the shot while giving the player great height when shooting.  Perfecting the jump shot also depends on producing spin on the ball while shooting. The second part of the essay deals with the question of what effect back spin has on the basketball when shooting. It is a common practice to shoot a basketball with back spin; my blog/research will answer what effect back spin has on the ball and in what ways and how back spin is produced on the ball. Within my question I’ll be asking how spin is produce in a shot, why back spin should be produced and how this helps when shooting.

To answer my question I will be using Biomechanics principles such as describing how Newton’s law works when performing a jump shot along with Magnus Effect and Projectile Velocity. These principles along with the skill fundamentals will assist help to explain how to perform the shot.

The following sub headings will help break down and explain how to perform an accurate jump shot:

Sub Headings:

What effect does back spin have on the basketball while shooting?

What effect does the height release point have on the accuracy of the shot?

How does projectile velocity affect the accuracy of the shot?

 

The elements and fundamentals of the jump shot

When shooting the ball an athlete will release the ball with a velocity appropriate to move the ball horizontally and vertically to the goal. Coaching manuals are fairly consistent in advising athletes to "square up" the body to the basket and jump vertically. A stable base of support would minimize horizontal motion of the body and create an accurate shot. The research suggests that coaches focus on a staggered stance and a vertical jump in teaching the jump shot.

When preparing for a jump shot, facing the basket ready to shoot, a player should ‘face up’. The feet do not need to be squared up in a parallel position. While this is not critical, it will help a player to take a balanced shot. Some players change their stance once they have mastered the shot, but beginning players need to align their trunk so that their shooting shoulder is forward and feet are evenly apart facing the basket. The stance can be evenly spread or slightly staggered and narrow.  Slightly staggering the stance allows the shooter a forward or backward motion while jumping and keeps the body upright for the shot. This also helps to keep the body aligned with the basket. With either stance it is recommended to jump from a moderate countermovement. When jumping there should be a knee flexion of 115-120 degrees. Before jumping the shooting side foot should be slightly forward and having feet slightly pointed outwards will provide a stable balanced base for the jump shot.

More advanced players have slight changes in techniques to produce longer shots; this may include a slight change in forward movement or less horizontal shift in the shooter’s centre of gravity. It is better to jump as vertical as possible with a stable base. It is suggested that to achieve best results the shooter should keep the ball, wrist, elbow and shoulder aligned with the target basket. It is believed that the traditional jump shot stance of squaring up to the basket can make it difficult to achieve a consistent shooting form. It is recommended to developed players to have staggered stance so that they can align the shooting hand and arm with the target basket.

Some players have a high release point when shooting the ball; this can increase the chance of accuracy due to the height of release. When a player releases the ball from a higher point it decreases the distance the ball must travel to the target. It also decreases the ball velocity and increase the angle of the basket making the chances of the ball going higher.
 
slow motion jump shot - showing the fundamentals of an accurate shot. 
 
The progression of the jump-shot
Pull up position, knee bend, extend arms, backspin-release ball
 

 


Figure 1

To achieve this outcome there are also biomechanical principles that help execute the shot. They are the following:

Why use back spin on the ball when shooting?

Magnus Effect

The Magnus effect places spin on the ball. It does this because the top of the basketball spins over the bottom of the ball which produces topspin.  The air on top of the ball slows down while underneath the air moves quicker. This causes pressure on top to be higher. This causes the Magnus force to help the ball dip towards the basket.  In biomechanics terms “The boundary layer would separate earlier on the top of the ball, because of the collision of the air travelling around the ball with the oncoming air, whereas on the bottom it would separate later, so some of the air from the underside of the ball would be dragged upwards behind the ball”. This causes the air above the ball to push the ball down along with conservation of momentum (Newton’s third law).

 Placing back spin on the ball increases the chances of making the basket. The ball is designed to spin back off the ring or back board if the ball is slightly off target. The basketball is designed to spin due the texture and design of the ball. When spin is placed on the ball it cause the ball to fall away or ‘break’; this is due to the Magnus force causing the change of direction. “The downward reflection of the ball accelerates because the lift forces not only act downward with gravity, but backward.”(Knudson 2007). This slows the ball down which allows the ball to have more downward fall or break.

                                                    showing the Magnus Effect on a ball


Figure 2

 

To produce back spin on a basketball there are some easy steps to follow. Back spin can become second nature to an athlete but they must learn how to do it properly so that they utilise skill in order to benefit their shot.

Equations

Bernoulli’s equation, p + 1⁄2 ρv2 + ρgh = constant

conservation of momentum, m1v1 = m2v2

Description – Backspin

1. Have your shooting hand underneath the ball with the ball sitting on the palm of your hand. Have the fingers spread evenly pointing upwards, the position of your dominant hand will have the biggest effect on the amount of spin that is produced. Place the non-dominant hand to the side of the ball so that it is supported - this acts as a guide.   Some shooters will place the tip of their middle finger on one of the horizontal seams to help ensure they get backspin on a shot. Some shooters can position their hands in this way while the game and clock is running. Many players will position the tip of their middle finger on the horizontal seam while shooting a free throw. This is because they have more time to position the hands in the right spot.

2. The shooter should form a 90-degree angle at the elbow (dominant hand) as they get ready to shoot the ball. There should be a 90 degree angle at the elbow and a 90 degree angle at the armpit.  Making the 90 degree angle allows the shooter to fully extend the arm as they make the shot.

3. The shooter needs to extend their arm and snap their wrist in a downward motion in order to produce backspin on the ball. As the shooter brings their fingers down, the fingertips should push the ball out of their hands, while doing this the shooter should pull the seams of the basketball downward. This creates the backspin on the ball. The middle finger (of the dominant shooting hand) should be the last one (finger) to come off of the ball while the shot is being made. This middle finger has the most impact on the direction and backspin of the ball.

 

How does projectile velocity affect the accuracy of the shot?

When taking a basketball shot you are trying to achieve a high release point so that you can project the shot at the highest point so as the ball falls away it goes through the hoop. When describing the projection of the basketball you need to work out the relative height of the projection. This is the projection point of the ball and where you want the ball to land. If the projection release point of the ball is lower than the target of the hoop, the relative height is negative.  Due to the relative height being negative the shooter must give the basketball ball extra flight time. This is done by increasing vertical velocity of the ball and the angle of projection (Blazevich 2007).


Projectile velocity of a shot 
Figure 3

 

What effect does the height release point have on the accuracy of the shot?

When producing the jump for the jump shot, the player is applying Newton’s first, second and third laws and the Law of Gravitation. The first law is applied when the player overcomes inertia by having a force applied against him, which is Newton’s second law, F=ma. To achieve the jump the player needs to “apply a large and well-directed force against the Earth” (Blazevich, 2007). This action applies Newton’s third law of an equal and opposite reaction force against the player. Since the force of gravity is acting downwards the player must produce a large vertical to jump high to increase his point of release while maintaining a vertical trunk position.

 

Equations (example) Newton’s Laws

speed = Δd/Δt

velocity (v) = Δs/Δt (rω for a spinning object)

acceleration (a) = Δv/Δt

inertia = m

m·s-1 to km·h-1: x m·s-1 /1000×3600

km·h-1 to m·s-1: x km·h-1 ×1000/3600

 

The effect of Centre of Gravity

The centre of gravity can affect the height of release. When the body stretches out for the jump shot there is less gravitational pull because of the extension of arms. When the body is fully extended with arms above the head there is more time in the air. This helps to give the player more time to make the shot.  “By bringing our legs up under our body after we leave the ground during a jump we would normally be about to fall back down towards the ground under the influence of gravity, we rapidly extend our legs downwards, and so, to conserve momentum, our upper body moves upwards (Blazevich 2007).”  This means that while the player’s body’s centre of mass is moving downwards, their upper body is moving upwards, relative to their lower body. Therefore their upper body briefly remains stationary or ‘hangs’.

 

Answer/Conclusion

To answer my question “What are the biomechanics behind an accurate jump-shot?” it is a combination of skill technique and biomechanical principles that makes an accurate shot. If you analyse a basketball player from the NBA for example Ray Allen, you will see that form of Ray Allen is similar to the description throughout this Blog. The extension that he reaches to shoot the ball and the angular range of his elbow to when he snaps the wrist while shooting is the reason why he is one of the best jump shooters in the NBA. Biomechanics of this skill is a combination of Newton’s 1st, 2nd, 3rd law along with achieving the correct the projectile velocity and producing back spin and understanding the Magnus effect and how much spin should be placed on the ball. When all these principles are combined, an effective and accurate jump shot can be achieved.

How are these elements of basketball used in other sports?

The different elements of the jump shot can be used in a range of actions in a variety of sports. The Magnus force which produces back spin on the ball can also be used in other sports. In cricket a fast bowler uses the Magnus force when he rolls his finger down the seam of the cricket ball. By doing this his middle finger is the last contact point of the ball, similar to producing a basketball shot. This back spin is also produced by snapping the wrist as the ball leaves the hand. These elements are two major factors that help produce the back spin motion in ten pin bowling, cricket (bowling), baseball (pitching) and tennis for example. Different biomechanical actions that are used in basketball are used in sports such as volleyball or netball. The vertical leap that is produced is a more compact version to a volleyball spike or block due to the athlete producing a large well directed force against the surface and then extending their vertical leap. There are many elements of the jump shot that can be used in other sports, once you break down the shot; you see the similarities due to the action and the principles. The principles are used in many sports but in different ways.

 

References:

Blazevich, A. (2007) Biomechanics the Basics: Optimising human performance. (1st ed) Chapters 3, 6, 13,. London, UK.

Callaway, C. (2012) LiveStrong. How to get backspin on a Basketball. Viewed 18 April 2013                   < www.livestrong.com/article>

Fontanella, J. (2007) International Journal of Sports Science & Coaching, Volume 2, Number 2. The Physics of Basketball. Baltimore, USA. pp. 197-200.

Knudson, D. (1993) The Journal of Physical Education, Recreation & Dance, Biomechanics of the Basketball Jump Shot - Six Key Teaching Points. pp 67 -72, Vol. 64, No. 2.

McGinnis, P. (2005) Biomechanics Of Sport And Exercise. (2nd ed.) Torques and Moments of Force Maintaining Equilibrium of Changing Angular Motion. USA.  pp. 134-136