Biomechanical Principles

Base of Support and COM:

In stage one, by having the correct stance and positioning it achieves a more stable base. It is more stable because the centre of mass (COM) is closer to the ground. The COM is described as the point of the body in which the mass is evenly distributed in every direction; and it moves out of the base of support the body is less stable and may cause the body to be unbalanced (Blazevich, 2017). So, by having the COM closer to the ground it results in a more stable base so the athlete is more balanced.

Levers

In stage two and stage three, they involve flexion and extension of the upper body and lower body muscles which relates to lever systems and lever length. Majority of the movements in the human body are classified as 3rd class lever systems. In the 3rd class lever system, the effort is the middle component which lies between the load and the fulcrum. One example of a 3rd class lever system is both flexion and extension of the knee joint and biceps brachii. A basketball free throw uses 2 types of 3rd class lever system to gain power and shoot the ball in the rim. A 3rd class lever is shown in Figure 2. The fulcrum is in the elbow joint, the effort is where the triceps muscle connects to the forearm and the load is where the ball is being held. The second type of 3rd class lever mainly focuses on accuracy of the shot. It is like the first type, however the effort is where the tendon from the forearm connects to the hand and its load is where the ball is held. The lever length is an important factor because depending on the lever length it can be either a biomechanical advantage or a biomechanical disadvantage. For a basketball free throw it would be more advantageous for the athlete to have longer levers so they can produce more height so the shot will be easier to make. On a side note, being taller in basketball is generally more advantageous as the additional height would help with defending positions when trying to intercept the ball and for attacking positions when trying to score.

Figure 2. 3rd class lever system.

Torque

Torque or momentum of force is the magnitude of the force causing the rotation of an object. Momentum of force refers to applying a force at a distance from the pivot point which are the force caused by the movement of the knees, arms and elbows. For example, biceps brachii is a muscle that produces forces during a free throw as the arm flexes and extends to apply force for the ball to travel a certain distance.

Potential Energy to Kinetic Energy

Potential energy is the energy that is associated with position and kinetic energy is the energy that is associated with motion. Within potential energy, elastic energy is stored within the tendons. So, in stage three, the elastic energy is stored in the tendons in the arms during the flexion phase in Stage 2 and is transferred into kinetic energy during the arm extension in this phase.

Kinetic Chain Movements

A kinetic chain describes the different body segments and the connected joints and muscles that work together to produce different movements (Sanchez, 2019). The kinetic chain can either be open or closed depending on whether the distal end of the body segment is fixed or if it can move without restrictions. In stage four the optimal technique is using a push-like movement rather than a throw. This is a closed kinetic chain because all joints are extended at the same time in a single movement. The push-like movement is easier to control and has a higher level of accuracy as the ball will be thrown using two hands. According to Blazevich (2017), it produces more force due to the torques that are generated at each joint resulting in the overall force being higher. The push-like movement generally results in a straight line (Blazevich, 2017) so this means that the ball being thrown will be straight and result in a more accurate score. On the other hand, a throw is much less accurate as the ball is thrown with one hand and it is faster than a push-like movement. A throw is an open kinetic chain which means that all of the joints are extended in a sequence one after the other (Blazevich, 2017) and is less accurate. A throw has a higher velocity due to the quick flexion of the wrist. Bartlet (2000) states that this type of throw is one of the quickest joint rotations in the human body. While a throw can reach higher velocities than a push-like movement, it is much less accurate to use for a basketball free-throw and therefore a push-like movement is the optimal technique to use when performing this skill. This type of movement also results in the ball having a backspin.

Magnus Effect

Magnus effect occur when the ball grabs the air that flows past it because of the friction between the air and the ball. The air particles start to spin the ball causing it to slow down or move faster and further (Blazevich, 2017). Slow-moving air is associated with higher pressure whereas faster-moving air is associated with lower pressure which is called pressure differential (Blazevich, 2017). A ball without a spin will continue to be at a high speed causing the ball to bounce back out over the front of the rim. However, a shot with a backspin will slow down as it hits the rim and will have a high chance of going in the rim (Orzel, 2017).

 

 

 Figure 3. Magnus Effect on the basketball free throw.

Figure 1 shows the pressure differential on the basketball free throw. The basketball is travelling through the air in the right direction towards the basketball with a weight vector going both up and down. The backspin producing force pushing the ball in the upwards direction, but the mass of the ball is heavier so gravity still pulls it in a downwards direction.

Relative Release Height

Relating to stage four, the relative release height is an important factor to consider when performing a basketball free throw. The relative release height is defined as “the vertical distance between the projection point of an object and the point at which it lands” (Blazevich, 2017). If the point in which the object is released is lower than the surface that the object will be landing on, then the relative height of projection is negative (shown in Figure 3.). If the height of the release point is higher than the point where the object will be landing, then the relative height of projection is positive (Shown in Figure 4.). For the basketball free throw, the relative height of projection is negative because the ball is being thrown into the basketball ring, which is much higher than the height of release when the ball is being thrown by the player. Figure 3 and Figure 4 model the two different relative release heights with the different landing positions. For our videos of an athlete doing 10 attempts from the free throw line and the 3 pointer line, the relative release height will be the same due to having the same athlete perform each attempt. The relative release height was calculated by measuring the athlete’s height (from feet to collarbone) and then added the arm length (shoulder to finger tips). This means that the optimal release and would stay the same. However, if the athlete was taller than the optimal release angle would slightly decrease and if they were shorter the optimal angle would slightly increase to improve their performance of this skill.

Figure 4. Negative relative release height.

Figure 5. Positive release height.

Angle of Release

This biomechanical principle relates to stage four where the ball is released with a push-like movement, with a negative relative release height. The optimal angle of release is determined by the range and the relative height of projection. The optimal release angle for a basketball free throw is generally 55 degrees. This is supported by (Blasevich, 2017) who states that the optimal angle for a negative release height is more than 45 degrees, but can be between 45 and 60 degrees. This is shown in Figure 6.

Figure 6. The effect of the release height on optimal projection angle (Blazevich, 2017).

In relation to the results in Table 1 for the free throw attempted from the free throw line, this optimal angle of release showed to be mostly accurate. For example, all of the attempts that had the ball land in the basketball ring ranged from the angles of 48 degrees to 58 degrees with the release velocity ranging from 4.78m/s and 5.60m/s. However there were 3 other attempts that were in between those optimal angles and yet did not score, and the release velocities were also in similar so that did not help with the explanation. Usually if the velocity was higher than it would affect scoring because the ball would have more force behind it and would most likely be thrown at a lower angle and would rebound off of the backboard; whereas if the ball was thrown softer, it would usually be thrown at a higher angle and go straight into the basketball ring. But, neither of these factors help to explain why some of the attempts from the free throw line went in and some did not even when the release angle and release velocities were similar. This also happened with the attempts from the 3 pointer line, where the attempts that scored had angles that ranged between 47 degrees and 51 degrees, with release velocities ranging between 4.84m/s ad 6.03m/s. This shows that the release angles were slightly lower and the velocities were slightly higher to make up for the longer distance that needed to be covered. There was no reason we could find that would explain these results.