Chapter 3 Biomechanical Properties

Biomechanics

study of the mechanics as it relates to the functional and anatomical analysis of biological systems

study of human movement

mechanics

the study of physical actions of forces and energy of bodies (static and dynamic)

Static

Constant state of motion (at rest or constant velocity without acceleration)

Dynamics

systems in motion with acceleration (unequal and unbalanced forces)

Kinetics

study of forces that inhibit, cause, facilitate, or modify motion of a body (gravity/friction)

Kinematics

study of the spatial and temporal characteristics of motion (velocity)

Kinetic Perspective

How much force was absorbed? (HOW)

Kinematic Perspective

How fast? (WHY)

Machines

used to increase or multiply the applied force in performing a task or provide a mechanical advantage

Machines function in four ways

- balance multiple forces

- enhance force in an attempt to reduce the total force needed to overcome a resistance

- enhance range of motion and speed of movement so that resistance may be moved further or faster than the applied force

- alter the resulting direction of the applied force

3 types of machines in producing movement

- levers

- wheel-axles

- pulleys

Levers

- Lever: rigid bar that turns about an axis of rotation or a fulcrum

- Axis: point of rotation about which lever moves

Levers in the body

Bones are the bars, joints are the fulcrum, muscles apply the force

First Class Lever

- When the axis (A) is placed anywhere between the force (F) and the resistance (R)

- designed to produce balanced movements when the axis is midway between force and resistance (ex. seesaw)

• when axis is close to force, lever produces/multiples speed and range of motion/distance (triceps in elbow extension)

• when axis is close to resistance, lever produces/multiples force motion (crowbar)

Second Class Lever

- resistance is between axis and force

designed to produce/multiply force movements, large resistance can move relatively small force

Third Class Lever

- force is placed between axis and resistance

- designed to produce/multiply speed and range of motion/distance

most common lever type in the human body

Torque and Length of Lever Arms

longer the lever, more effective it is in imparting velocity (produce more linear force)

Quickness and Lever Arms

shorter is better

Wheels and Axles

When wheel turns, axle turns

ex. glenohumeral joint (internal and external rotation)

• wheel: forearm, wrist, and hand

• axle: shaft of humerus

Single pulleys

Single pulleys have fixed axle and function to change direction of force application

Friction

force that results from resistance between the surfaces of two objects moving on each other

ex. running (increase friction of feet and the ground to exert force and propel forward)

ex. skating (decrease friction to slide across ice with less resistance)

Balance, equilibrium, stability

base of support

• larger base of support, greater stability of object