Applied Biomechanics and Kinesiology

• Applied biomechanics applies the principles of mechanics to biological systems such as the human body
• Kinesiology is the study of human movement
• These fields are foundational for understanding how the body functions during various activities and under different conditions

Biomechanical Principles

• Biomechanics uses physics principles to study movement and posture
• These principles include:
  • force
  • motion
  • leverage
  • stability
• Understanding these principles is essential for analyzing human movement

Kinetics vs. Kinematics

• Kinetics:
  • focuses on the forces that cause motion
  • examines internal forces, such as muscle force, and external forces, such as gravity and ground reaction force
• Kinematics:
  • describes motion without considering the forces that cause it
  • includes displacement, velocity, and acceleration

Types of Motion

• Linear motion: movement in a straight line
• Angular motion: rotation around an axis
• General motion: a combination of linear and angular motion (most human movement)

Force

• A force is a push or pull that can cause a change in an object's motion
• Forces have both magnitude and direction, making them vector quantities
• Key forces in biomechanics:
  • gravity
  • muscle force
  • joint reaction force
  • external resistance

Levers

• Levers are rigid structures that pivot around a fixed point (axis or fulcrum)
• They are used to increase the mechanical advantage of muscle force
• The human body contains three classes of levers:
  • First-class levers
    • the fulcrum is located between the force and the resistance (e.g., seesaw)
  • Second-class levers
    • the resistance is located between the fulcrum and the force (e.g., wheelbarrow)
  • Third-class levers
    • the force is located between the fulcrum and the resistance (e.g., bicep curl)
• Most levers in the human body are third-class, which favor speed and range of motion over force production

Stability

• Stability refers to the resistance to disruption of equilibrium
• Key factors affecting stability:
  • Base of support
    • larger base of support increases stability
  • Center of gravity
    • lower center of gravity increases stability
  • Line of gravity
    • stability is greatest when the line of gravity falls within the base of support
  • Mass
    • greater mass increases stability

Kinematic Variables

• Displacement:
  • change in position
  • a vector quantity
• Velocity:
  • rate of change of displacement
  • vector quantity
• Acceleration:
  • rate of change of velocity
  • vector quantity
• Speed:
  • rate of motion
  • scalar quantity
  • magnitude of velocity

Kinetics: Forces and Motion

• Newton's Laws of Motion:
  • First Law (Inertia)
    • 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 a force
  • Second Law (Acceleration)
    • the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass (F = ma)
  • Third Law (Action-Reaction)
    • for every action, there is an equal and opposite reaction
• Momentum:
  • product of mass and velocity
  • important in analyzing collisions and impacts

Work, Power, and Energy

• Work:
  • force applied over a distance (Work = Force × Distance)
• Power:
  • rate at which work is done (Power = Work / Time)
• Energy:
  • capacity to do work
• Types of energy:
  • kinetic energy (energy of motion)
  • potential energy (stored energy)

Muscle Biomechanics

• Muscle force:
  • force generated by muscle contraction
  • depends on factors such as muscle size, fiber type, and activation level
• Muscle moment arm:
  • distance between the muscle's line of action and the joint center
  • affects the muscle's ability to produce torque
• Force-velocity relationship:
  • muscle force decreases as contraction velocity increases

Joint Biomechanics

• Joint reaction force:
  • force exerted by joint surfaces on each other
  • includes both magnitude and direction
• Joint stability:
  • resistance to abnormal joint displacement
  • influenced by factors such as ligament integrity, muscle force, and joint geometry
• Range of motion:
  • angular distance through which a joint can move
  • varies depending on joint structure and individual factors

Gait Analysis

• Gait:
  • manner of walking
  • involves a cyclical pattern of movements
• Gait cycle:
  • sequence of events from one heel strike to the next heel strike of the same foot
• Phases of gait cycle:
  • stance phase
    • when the foot is in contact with the ground
  • swing phase
    • when the foot is not in contact with the ground
• Gait parameters:
  • stride length
  • step length
  • cadence (steps per minute)
  • walking speed
• Analyzing gait can provide insights into:
  • musculoskeletal function
  • neurological disorders
  • effectiveness of interventions

Techniques for Biomechanical Analysis

• Motion capture:
  • uses sensors to track body movements
  • provides data on joint angles, velocities, and accelerations
• Force plates:
  • measure ground reaction forces during activities such as walking or jumping
• Electromyography (EMG):
  • measures electrical activity of muscles
  • provides information on muscle activation patterns
• Computer modeling:
  • creates simulations of human movement
  • allows for analysis of complex biomechanical systems