Biomechanic Principles of a Jump-Shot

Major Question.

What are the biomechanical principles that dictate the effectiveness of a basketball jump shot?

The basketball jump shot is the most commonly utilised shot in the game of basketball today (Gels, 2015) with the two-legged jump shot now amounting to over 70% of the shots undertaken in a game (Struzik et al, 2014). An effective jump shot allows a player to elevate themselves above opponents, eliminating their opponents’ ability to defend the shot from taking place.

Biomechanics is the study of mechanics within biological systems (Blazevich, 2012) and as such, is used in a wide variety of sporting contexts to gain a greater understanding of the optimal performance of an athlete (Wood, 2010). This blog will identify and explain a number of biomechanical principles that take place within different aspects of performing a basketball jump shot and seek to identify the optimal technique used to execute this skill.

The Answer

The basketball jump shot is a skill that is made up of a variety of individual movement phases (see fig.1). These phases are-

·      The power production/take-off

·      The flight phase

·      The release

Figure 1. A basketball player performing the jump shot without a basketball (Struzik et al, 2014).

The power production/take-off

This phase is concerned primarily with applying a force strong enough to lift the athlete off the ground. To achieve this the athlete utilises Newton’s 3 laws of motion.

Newton’s first law states that-

“An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force” (The Physics Classroom, 2015).

This means that an athlete standing still will remain in that state of motion unless they are able to overcome this inertia by applying a force. This is where Newton’s second law of motion comes in.

“The acceleration of an object is proportional to the net force on it and inversely proportional to the mass of the object: F=ma” (Blazevich, 2012).

This law tells us that in order to accelerate faster or jump higher, an athlete needs to exert a bigger force upon the ground, as per Newton’s third law which states-

“For every action, there is an equal and opposite reaction” (Blazevich, 2012).

So, when an athlete applies a force downwards, whatever the athlete is applying the force to (in this case, the ground) will exert an opposite and equal reaction force against the athlete. It is important to note that as there is an equal and opposite reaction the force should be produced straight down to avoid the athlete jumping to the side (See figure 2).

 

 Fig. 2-The force should be produced straight down to avoid the athlete jumping to the side

So in order to jump higher and therefore have a greater chance of taking the shot out of reach of the defender the athlete needs to maximise force production downwards. This force is produced by the actions of the muscles. By utilising multiple muscle groups applied in the same direction and in the correct sequence an athlete is able to achieve the greatest force possible (Wuest and Bucher, 2009). This is known as the summation of forces. This summation of forces should utilise every major muscle group in the body in order to exert as much force as possible, however while arm-swing executed prior to take-off allows for athletes to reach greater heights (Hara et al, 2006) in the sport of basketball this arm swing is minimised due to the need to maintain control of the ball. 



Flight

While in the flight phase of the jump shot it is advantageous to the athlete if they are able to extend the period of time spent in the air. This is sometimes referred to as the “hang” time. This can be achieved by the athlete manipulating their centre of mass.

The centre of mass of an individual refers to the point at which the mass of the body is evenly distributed in all directions (Blazevich, 2012).

As described earlier, when an athlete jumps, a force (F) is applied to the ground to accelerate (a) their mass (m) upwards (Blazevich, 2012). The “hang” time often mentioned in sports is achieved by the athletes bringing their legs up underneath their body after leaving the ground. As the athlete’s centre of mass begins to move downwards, the legs are rapidly extended causing the upper body to remain stationary in relation to the lower body (Blazevich, 2012). This movement also allows for greater accuracy of the shot by keeping the head and eyes stationary throughout the shot (figure 3).

Fig. 3- A depiction of how the centre of mass (red circles) moves upwards when the legs of the athlete are brought up while the eye-line remains the same (adapted from Blazevich, 2012). 

Release

Projectile motion of an object refers to the motion of an object (in this case, a basketball) projected at an angle into the air (Blazevich, 2012). So what is the optimum projectile angle to release the ball at in order to score?

Figure 4 depicts the relationship between the projection angle of the ball and the entry angle of the ball into the hoop. It clearly shows that the higher the projectile angle of release (up to 90 degrees) the larger the target (shown as T).

 

Fig. 4- depicting the relationship between the projection angle of the ball and the entry angle of the ball into the hoop (Okazaki and Rodacki, 2012).

One factor that comes into the projection angle of an object is the relative height of projection. The relative height of projection is the vertical distance between the projection point of an object and the point where it lands (Blazevich, 2012). As a basketball ring has a height of 10 feet (3.048 metres) the relative height is negative. However this can be manipulated due to the height that the athlete releases the ball from. Therefore, the projection angle of the ball is largely dependent on the relative height of the projection with between 50-7 degrees being the best in order to maximise the entry angle of the ball.

One of the major factors that affect the success of a basketball jump shot is the spin that is applied to the ball at the release. By imparting backspin onto the ball through wrist flexion the horizontal velocity is decreased after it hits the backboard (Knudson, 1993).  This means that if the ball hits the rim/backboard it is less likely to bounce away from the basket and more likely to fall into the basket. This backspin imparted on the ball also has an influence in relation to the Magnus effect. The Magnus effect is a pressure differential caused by placing spin on the ball (in this case backspin). This pressure differential causes the ball to swerve or in this instance, lift. This lift produced by imparting backspin on the ball increases the angle of entry of the ball into the basket, which as seen in figure 4, increases the target size enabling for more accurate shooting. 

Where else can we use this information? 

These biomechanical principles have found their way into a wide variety of sports. The Magnus effect is used extensively in the application of swing bowling in cricket as well as a means of explaining the inevitable hook or slice an amateur golfer may unwillingly impart upon their shot. The knowledge of this effect has led to athletes gaining a greater understanding of what they can achieve with a balls flight pattern as extensively demonstrated in profession soccer with free-kicks. The knowledge of how to manipulate an athletes centre of mass can be seen in a wide variety of sporting situations such as the high jump and evasion sports while the understanding of projectile motion has impacted on at what angle and trajectory that are used to gain the most distance.



References

Blazevich, A. (2012) Sports Biomechanics the Basics: Optimising human performance. (2nd ed.). London, UK.

Gels, J. 2015. Basketball Jump Shot. The Coaches Clipboard Basketball Playbook. Retrieved from <http://www.coachesclipboard.net/JumpShot.html>

Hara, M. Shibayama, A. Takeshita, D. Fukashiro, S. 2006. The effect of arm swing on lower extremities in vertical jumping. Journl of Biomechanics. 2006;39(13):2503–2511.

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.

Okazaki, V. H. A., & Rodacki, A. L. F. (2012). Increased distance of shooting on basketball jump shot. Journal of Sports Science and Medicine, 11, 231-237

Struzik, A., Pietraszewski, B., & Zawadzki, J. (2014). Biomechanical Analysis of the Jump Shot in Basketball. Journal of Human Kinetics, 42, 73–79. doi:10.2478/hukin-2014-0062

The Physics Classroom. 2015. Newton's Laws - Lesson 1 - Newton's First Law of Motion. Retrieved from < http://www.physicsclassroom.com/class/newtlaws/Lesson-1/Newton-s-First-Law>

Wood, R. 2010. Sports Biomechanics and Kinesiology. Top End Sports. Retrieved from <http://www.topendsports.com/biomechanics/>

Wuest, D. A., Butcher, C. A. (2009). Foundations of Physical Education, Exercise science, and Sport. New York, NY: McGraw-Hill