Week 5 Kinetics and Kinematics

Biomechanics: The application of the principles of mechanics to the living human body.
Kinesiology: Combination of art and science; the study of human movement.
- Clinical Kinesiology: Application of kinesiology to environments of the health care professional.

To understand movement and the forces acting on the body and to learn how to manipulate these forces to:
- Prevent injury
- Restore function
- Provide optimal performance

Kinetics: Forces that produce or resist movement.
- Ground Reaction Forces: Forces exerted by the ground on a body in contact with it that can be monitored during a gait cycle. Example data:
- A graph showing load force during a normal gait cycle indicates that ground reaction forces peak around heel-strike and toe-off.

Kinematics: Types of motion or movement without regard for the forces producing the motion.
- Types of Motion:
- Linear Motion: Motion along a line where frictional forces play a role, influenced by the direction of translation.
- Curvilinear Motion: A path that curves like a wheel traveling on a rough surface, affecting the high and low points of translation.
- Osteokinematics: Movement of segments that make up a joint (e.g., tibia moving on femur).
  - Types: Translatory (movement in a straight path) and Rotary (movement around an axis).
- Arthrokinematics: Minute movements occurring within a joint and between joint surfaces. Examples include roll, slide, and spin movements.
- Degrees of Freedom: Number of axes about which a joint can move, categorized as uniaxial, biaxial, or triaxial joints.
- Joints include:
  - Uniaxial: Hinge or pivot (e.g., elbow).
  - Biaxial: Condyloid, ellipsoid, and saddle joints (e.g., thumb).
  - Triaxial: Ball-and-socket joints (e.g., hip).

Clinical Goniometry: Measurement used to quantify joint motion.
End Feel: Sensation perceived by the clinician when assessing passive range of motion at the end of a joint's range of motion; classified into three normal types: hard, soft, and firm.

Open Kinematic Chain (OKC): Distal segment is free to move (e.g., throwing).
Closed Kinematic Chain (CKC): Distal segment is fixed (e.g., pushing against a wall).

Kinetics: Study of forces that produce, stop, or modify motion.
Forces can be internal (within the body) or external (acting on the body from the environment).

Five variables to describe motion include:

Type: Translatory (linear displacement) or rotary (motion around an axis).
- Examples:
  - Translatory: Dropping a pen, rolling a ball, sliding hand.
  - Rotary: Flexing/extending the elbow.
Location: Defined by a plane of motion perpendicular to the axis of motion (z-axis, y-axis, x-axis).
Magnitude: Linear motion measured in meters or feet; rotary distance measured in degrees.
Direction: Can use terms like anterior, medial, lateral in the context of joints.
Rate of Motion or Rate of Change:
- Velocity: Rate at which motion occurs (measured as meters/sec for translatory and degrees/sec for rotary).
- Acceleration: Change in velocity (positive when speeding up, negative when slowing down).

Force: A push or pull that produces a displacement.
Torque: Force causing motion occurring about an axis; calculated as $T = F imes d$ , where $d$ is the distance from the location of force on a body segment to the joint (axis).
Four types of forces that affect body motion:
- Gravity
- Muscles
- Externally applied resistances
- Friction

First Law (Inertia): A body at rest will stay at rest, and a body in motion will stay in motion until acted on by an outside force.
- Inertia is the reluctance of a body to change its current state.
Second Law (Acceleration): Acceleration is proportional to the magnitude of the net forces acting on it and inversely proportional to the mass of the body,
- Expressed mathematically as $F = ma$ , where $F$ is net force, $m$ is mass, and $a$ is acceleration.
Third Law (Action-Reaction): For every action force, there is an equal and opposite reaction force (e.g., a basketball player jumping).

Multiple forces on a body can be combined into a resultant vector showing the overall effect. The resultant vector is the simplest force that produces the same effect as all forces acting on the body.

Levers: Rigid bars rotating about an axis, consisting of three main elements: Axis, Resistance force, and Moving force.
- In the human body, the axis represents joints and body segments act as levers.

First-Class Lever: Axis located between the force and resistance arm (e.g., seesaw).
- Example: Weight of the head acted on by muscle force.
Second-Class Lever: Axis occurs at one end with the force arm larger than the resistance arm (e.g., wheelbarrow).
Third-Class Lever: Axis located at one end with a force arm smaller than the resistance arm; most common lever type in the human body.
- This design allows for producing speed of the distal segment, able to move small weights over large distances.

Mechanical Advantage: Ratio between the length of the force arm and resistance arm, calculated as:
- $MA = rac{Force ext{ Arm Length}}{Resistance ext{ Arm Length}}$ . MA may be greater than, less than, or equal to 1.

Understanding forces helps to reduce stress to injured joints through gravity-minimized motion, like in hydrotherapy.
Center of Mass (COM): The point about which an object is balanced and the origin of gravity’s force vector, typically anterior to the S2 vertebra in adults.

Stable Equilibrium: Body returns to its original position after light perturbation.
Unstable Equilibrium: Body seeks a new position after perturbation.
Neutral Equilibrium: Center of gravity is displaced but remains at the same level.

Factors affecting stability include:
- Height of center of gravity above base of support
- Size of base of support
- Location of gravity line within the base of support
- Weight of the body.

The Star Excursion Balance Test is frequently used in clinical settings to assess balance and stability.

Pressure is defined as force per unit of area; optimizing pressure application can aid in tissue growth but excessive force may lead to injury.
Pressure is modulated by:
- Decreasing force magnitude
- Increasing area of application
- Reducing application time.

Calculations for tipping a cow involve forces with varying contributions from a person’s gravitational force through levers and angles.
Exemplar calculation shows that significant force is necessary as the mass of a cow and lever placements determine tipping success.

Understanding these concepts of forces, levers, motion, and the application of gravity is crucial for effective clinical practices and aiding patient rehabilitation. Emphasized were the influences of forces on the human body and practical applications that inform kinesiology and clinical kinesiology practices.