Unit 3 Kinesiology

Biomechanics

Science based (physics) field which focuses on movement efficiency and productivity and aims to understand and quantify the movement and function of the human body

Mass

Kg

Weight

N

Velocity

v, change in distance (m)/change in time (s)

Acceleration

a, change in velocity (m/s)/change in time (s). This means m/s/s or m/s²

Vector quantity

It has a magnitude (size) and direction

Force

A push or pull that acts upon a body, it is a vector quantity and it is measured in Newtons. 1N = 1 kg m/s2
Either external or internal

Gravity

A force that acts on objects pulling them toward the earth at a rate or acceleration of 9.8 m/s2

External forces

Originate outside the body or object being studied. Force acts on the body in a specific direction

Internal forces

Come from within the system. In our case the muscles of the human body. The muscles and skeletal structure provide a series of levers that are used to generate forces (Hint: Think concentric and eccentric contraction)

Newton's Three Laws of Motion

Sir Isaac Newton (1642-1727) described three laws of motion. These laws govern the relationships of how objects move. Form the basis for classical mechanics and therefore are important concepts to the field of biomechanics.

The First Law of Motion: Inertia

A body in motion tends to stay in motion and a body at rest tends to stay at rest unless acted upon by an external force. When an object is at rest, all of the forces acting upon it are balanced. Ground reaction force and gravity.

Inertia

The resistance for an object to change its state of motion, the bigger the mass the bigger the inertia

The Second Law of Motion: Acceleration

A force applied to an object causes an acceleration of that object of a magnitude proportional to the force and in the direction of the force, but inversely proportional to the object's mass. This is expressed as F=ma. F (N) = m (Kg) x a (m/s2)
(If the mass is the same, the bigger the force then the bigger the acceleration. If the acceleration is the same, the bigger the mass, the bigger the force. If the force is the same, the bigger the mass, the lower the acceleration and vice versa.

The Third Law of Motion: Action & Reaction

For every action, there is an equal and opposite reaction

Linear (or translational) motion

Movement occurs in the same direction as the force.
Examples are projectile motion. Human movement is relatively complicated, often many forces act in many different directions. Because forces are vectors, they can be added to provide a resultant force vector.

Angular (or rotational) motion

It is much more complicated to calculate and involves the movement or rotation about an axis. Human activities can involve rotation in three ways:
Rotation of projectiles or objects - Topspin in tennis.
Rotation of the entire body about one of the three axes - Gymnastic somersault.
Rotation of individual body segments - Movements about a joint when running.

General motion

A combination of both rotational and linear motion, human movement is normally general motion

Centric force

It will result in linear motion in the direction of the applied force

Eccentric force

(off-centre) force, can lead to rotational motion and also some linear motion. The resultant effect of this off centered force is often referred to as torque.

7 principles of biomechanics

Physics Concept:
Stability

Maximum Effort

Linear Motion

Angular Motion

Biomechanics Principles:
1. Stability

2. Production of Maximum Force
3. Production of Maximum Velocity

4. Impulse and Momentum
5. Direction of Application of the Applied Force

6. Production of Angular Motion (Torque)
7. Conservation of Angular Momentum

Principle 1: Stability

The greater the mass, the lower the center of mass to the base of support, the larger the base of support, and the closer the center of mass is positioned to the base of support, the more stability increases.

Center of Mass

(COM) is the imaginary point around which mass of an object is concentrated

Base of support

(BOS) is the area beneath an object that includes every point of contact that the object makes with the supporting surface

Principle 2: Maximum Effort

The production of maximum force requires the use of all possible joint movements that contribute to the task's objective

Principle 3: Maximum Effort

The production of maximum velocity requires the use of joints in order - largest to smallest

Impulse

As a force acting over a period of time or F 𝚫 t (equal to momentum, mv). The greater the force or the longer the time the force is applied leads to a greater impulse.

Momentum

The quantity of motion of a moving object or mass x velocity (mv). It is a vector and has quantity and direction. It is measured in kg.m/s

Inelastic collision

Ex. catching a ball, there will be some loss of kinetic energy within the system (heat, sound)

Elastic collision

Ex. ball bouncing

Collision

Occurs when an moving object makes contact with another object (moving or stationary)

Perfectly elastic collision

There will be no net loss of kinetic energy within the system

Conservation of momentum

The total momentum of a system is the same before and after the collision

Principle 4: Linear motion

The greater the applied impulse, the greater the increase in velocity

Principle 5: Linear motion

Based on Newton's 3rd Law (Action/Reaction), movement of the human body usually occurs in the direction opposite to the applied (action) forces

Lever

Simple machines that perform tasks using the physics principle of Torque (turning force). Consists of 3 parts - Fulcrum, Load and Force.
Balancing 2 or more forces, providing a force advantage where a heavy load can be lifted with less effort, and provide a speed advantage where a load is moved farther and faster than effort
1st, 2nd, and 3rd Class Levers

Principle 6: Angular motion

Angular motion is produced by the application of a force acting some distance from an axis; that is, by torque. An eccentric force that applied to a body/object makes it rotate about an axis.

Torque

An eccentric force that applied to a body/object makes it rotate about an axis. The resulting force created by the "turning effect". It will produce angular motion and depends on 3 factors:
- Magnitude of the applied force.
- The length of the lever arm.
- The angle at which the force is applied to the lever arm. Optimal angle would be perpendicular to the lever arm.

Principle 7: Angular motion

It's constant when an individual or object is free in the air. Also, it's created when a mass is rotating (angular velocity). This is a very similar concept to linear momentum (P=mv).

Moment of inertia

Just as in Newton's 1st Law the resistance of a body to rotate or rotate constantly without external forces acting upon it is known as moment of inertia.
Changes in the distribution of mass, change the moment of inertia.

Functional movements

These are based on real-world situational biomechanics. They are the types of movement patterns that we make each day and involve multi-planar and multiple joint movements. Can be done qualitatively through observation or quantitatively through measurement. Experts in the field will normally use a combination of both methods in order to make recommendations about movement patterns.

Qualitative analysis

Description and analysis of movement by using non-numerical methods. Observation and evaluation of the execution of a specific individual skill. Visual observation is the most common method. However, this relies on the expert and thorough understanding of the biomechanical principles and movement patterns being assessed. Comparison between the individual movement performance with an expected or ideal skill or movement pattern, acquired through years of experience. Use a framework

Framework

A tool used to systematically evaluate performances

Pros of qualitative analysis

- Easy to conduct in many different settings.
- Little or no equipment required.
- Immediate verbal or visual feedback can be required about the quality of performance.
- Over time with repetition the performer can begin to assess their own performance based on feedback provided.

Cons of qualitative analysis

- Dependent on the observer's knowledge. Reliability and validity can be questionable.
- Observer bias can influence the outcome.
- The nature of the skill or movement may be difficult to observe with the human eye.

Quantitative analysis

Relies on use of instruments to generate numerical data to measure and quantify movement being observed.
Often relies on video software and other equipment which will be able to assign numerical values to the movement. Focuses on aspects such as time, distance, velocity, acceleration, angles and power.

Computerized Motion Analysis

Coach's Eye is a great example of the many software programs that simplify quantitative analysis for everyday users. Allows skills to be "biomechanically" broken down and replayed in slow motion. Can make qualitative feedback more "quantitative".

Key to Video Capture in Analysis

- Use Tripod
- Film from distance to capture all of desired movements in frame without having to move (pan) camera.
- Use appropriate analysis software where possible.
- Capture distances and other measurements to be used in analysis.

Pros of quantitative analysis

- Don't rely on immediate knowledge that an observer has stored in their head. Experts can operate equipment to extract objective data.
- Instruments in good working order can provide high degree of accuracy and reliability.
- Can capture complex movements at rapid speeds for later analysis.

Cons of quantitative analysis

- Often expensive equipment and software.
- High degree of technical and skill required by analyzer.
- Might be restricted to laboratory use. Dependent on skill and equipment.
- More time-consuming to complete.