DEFINING BIOMECHANICS

Biomechanics: involves the study of how the body moves

• Relates body motion to the anatomical and physiological processes in the human body

Mechanics: the study of physical movement that results from forces

• Contains two divisions

• Statics : the study of systems that are in a consistent state of motion. This could mean at rest or in motion. In homeostasis

• Dynamics: study of systems that are in motion with acceleration. Entire system is not in homeostasis

Kinematics and Kinetics: additional components in the field of biomechanics

• kinematics : describing the characteristics in motion (displacement, velocity, time, etc.)

• Kinetics: study of forces that are associated with movement of the human body

The human body acts as a machine

• Bones and muscles work together to create movement

• The goal of the machine is to work in a cohesive unit to provide a mechanical advantage

• Ability to apply small amount of force in order to overcome a large amount of resistance

• Mechanical advantage = force or resistance

Four functions of machines

• Balance multiple forces

• Reduces the amount of force needed to overcome a given resistance by enhancing the force

• Increases the speed and/or distance of the given resistance enhancing range of motion

• Alters the overall direction of the force being applied

Simple machines

In the human body there are three types of machines that provide movent

• Each machine balances a rotational force about the axis

• Levers ( most common )

• wheel/axles

• Pulleys

Levers (most common) : rigid bars that turn about an axis of rotation

• Axis of rotation is the same thing as a fulcrum

• Force against a resistance causes the lever to rotate

• Include  force, resistance, axis

• First class levers

• Purpose : assist in balanced movements

• Location of the axis in relation to the force and resistance changes the mechanics of the movement

• The type of lever can change for any given body part by altering the body's position

• If the axis is in the middle it is first class

• see-saw

• Second class lever

• Produce force movements

• Move a larger resistance with relatively little force

• pushup

• Third class lever

• Produce speed and range of motion movements

• A great amount of force is required in order to move a relatively small amount of resistance

• Most common type of lever

Factors that influence anatomical levers

• Torque

• Length of lever arm

• Wheels and axles

• Pulleys

Torque: the tendency of a force to cause a rotational movement around the axis.

Effects the eccentric force

→ eccentric force is an off-balance force. Applied away from the center of rotation

→ rotation does not occur without the presence of an eccentric force

→ muscles put eccentric force on the bones causing them to rotate on the axis (joint)

→ calculated as - force magnitude X force arm

• Force magnitude = amount of force

• Force arm = distance between application of force and axis

→ resistance arm: distance between axis and point of resistance application

Wheels and Axles: used to enhance range of motion as well as speed of movement

→ basically function as a lever

→ center of wheel and axle = fulcrum

→ radii = force arms

→ mechanical advantage = radius of the wheel/radius of the axle

Pulleys: a single pulley has a fixed axle

→ changes the effective direction of force application

→ a single pulley has the mechanical advantage of one

• Using more than one increases the mechanical advantage