Biomechanics Introduction Week 2.1

Biomechanics definition

mechanical concepts applied to human body/function

• application of anatomy & kinesiology to produce movement

Break down the word Biomechanics

Forces and mechanisms. Movement related to function, forces and physics

Arthrokinematic motion

Manner in which joints move in relation to each other

Osteokinematics

Manner in which bones move in space (flexion, extension)

Arthro- prefix definition

joints

Osteo- prefix definition

Bones

Force equation

F = mass x acceleration

Force definition

magnitude of push or pull action

Mass definition

the amount of matter a body contains

• How big?

Scalar

Describes only magnitude, and NOT direction, will be a single number of units

• has no direction

Example of scalar things

• Mass

• Temperature

• Distance

• Time

Vector definition

Measure of magnitude or direction

Example of vector things

• Velocity

• Force

• Acceleration

Inertia

A resistance to a change in motion

Kinetics

forces causing movement in a system

Torque

Force that produces rotation around axis

Friction definition

Force developed by 2 surfaces rubbing, sliding, or rolling against one another

• works to prevent motion

Does Friction exist when 2 objects are in contact?

Potentially

Does Friction exist when 2 objects are rubbing together?

Yes, Always!

Give an example of Vector vs. Scalar as it pertains to speed.

60mph is scalar, but 60mph North is a vector because it includes direction as well

Velocity definition

the speed of an object combined with a certain direction

When is movement created with force?

When one force becomes greater than another

Types of Force

• Compression or Push

• Tension/Distraction or Pull

• Shear

Linear force definition

Can push or pull along a straight line on an object. Forces act along the same linear path.

• Push and pull line

Examples of Linear force

• Pulling a rope

• Pushing a box

• muscles pulling on a bone

What does linear force result in?

• Causes an object to move, stretch, or compress in one direction

Parallel force definition

Occur in the same plane in same or opposite directions

• NOT on the same line/level

In a parallel force, where is the opposite force located?

Between the two parallel forces

Example of parallel force

3 point splint

Concurrent forces definition

Act on a common point, but in different directions

Resultant force definition

Overall effect of the 2 concurrent forces

Examples of biomechanics/concurrent forces

• Two people pulling a boat from different points in order to achieve the same action

• 2 person transfer

• Using two hands to turn while sitting in a wheelchair

Force Couple

Two or more forces acting in different directions

• resulting in a turning effect

What type of movement does a force couple result in?

turning effect

Give an example of a force couple

Raising the shoulder

• movement of upper trapezius, lower trapezius and serratus anterior

Vector composition

2 or more forces can be added together

What does the amount of torque depend on?

Torque = distance x force

• The more distance, will require more force. The same vice versa.

Stability

When all torque is even, and gives you a state of equilibrium

Center of Gravity

a point at which all planes of the body intersect.

• Currently is at your waist when standing up.

What are the 4 types of Equilibrium

• Stable equilibrium

• Unstable equilibrium

• Neutral equilibrium

• Static equilibrium

Stable equilibrium

When an object is in a position where disturbing it would require it’s Center of Gravity to be raised

• ex: a brick

Unstable equilibrium

Only a slight force is needed to disturb an object

• ex: pushing over a phone that is balanced upright

Neutral equilibrium

an object’s Center of Gravity is neither raised nor lowered when it’s disturbed

• ex: a ball rolling on a flat surface

Static equilibrium

The object is not moving

• the additive of all forces acting on a mess is equal to ZERO

BOS definition

Base of support

• part of the body that is in contact with supporting surface

LOG definition

Line of gravity

• imaginary vertical line through the center of gravity toward the earth

What can you do to improve stability?

• Lower COG

• Keep COG and LOG over BOS

• Make BOS wider

• Increase mass

• Increase friction

• Focus on stationary object

Do smooth surfaces or rough surfaces make more friction?

Rough surfaces make more friction

The greater the friction between two surfaces the greater the _____ .

Stability

Law of Inertia - Newton’s First Law

A body at rest will remain at rest, and a body in motion will remain in motion in a straight line with constant velocity unless acted on by an outside force

• net force acting on the object should be 0

How do you move an object out of its state of inertia?

Need to generate force that is a greater mass than inertia

The greater a body’s inertia the ______ it is to change its velocity

harder

Force equation

F = mass x acceleration

Law of Acceleration - Newton’s Second Law

an object with a force acting on it will accelerate in the direction of that force

• magnitude of acceleration is directly proportional to the force applied, and in the exact direction of the applied force

Law of Action - Newton’s Third Law

For every force there is an equal and opposite reaction force

• equal in magnitude (strength), and opposite in direction

6 types of Simple Machines

• Incline plane

• Wedge

• Screw

• Wheel and Axle

• Pulley

• Lever

What are the components of a Lever?

A (axis) > Joint

R (resistance) > Weight

F (force) > Muscle

What is the lever?

Bone in the body

First Class Lever

Axis is in the middle

• Like a seesaw

• Fulcrum : middle

• Effort: one end

• Load: other end

Real Example of First Class Lever

Neck extension

• Balancing the weight of your head. The fulcrum is in the middle, head weight is going back one one end, the effort is pulling down tilting your head up

Force arm (FA)

Distance between the axis and force

Resistance arm

Distance between the Resistance (R) and Axis (F)

How can you use splinting to reduce pressure?

Make a longer splint, this will increase the area of force application

How can you use splinting to increase the mechanical advantage?

Control parallel force systems

Short term stretch is _____

elastic - return to pre-morbid state

Long term stretch is ______

plastic - deformation retains some degree of stretch position

Too much force on tissue can do what?

• May tear tissue, stimulate inflammation, increase edema, increase fibrosis

Second class Lever

• Resistance is between axis and Force

• From left to right

  • Fulcrum > Resistance pushing down > Effort lifting up

    • Wheelbarrow

Which lever is found the most in the body?

Third Class Lever

Example of the Second Class Lever

• Wheelbarrow

• Tweezers, Chopsticks

• Ankle joint when going into plantar flexion

  • Gastrocnemius is the effort

  • Resistance is the weight going down onto the toe

Third Class Lever

Force is between axis and resistance

• From left to right

  • Fulcrum/axis (Joint) > Effort (Muscle) > Load (Resistance)

Third Class Lever Example

• Hammer curls

• Bicep Curls

• Hamstring curls

Mechanical Advantage (MA)

Ratio between force arm and resistance

• Shorter arm requires more force

• Longer arm requires less force

Pulley definition

a spool or wheel that turns around the axis. Pulley amplifies the muscle movement

• Pulleys increase force, as in hoisting or pulling heavy weights

Example of a Pulley

• Patella is a pulley for the quads

• amplifies the muscle movement

Wheel and Axle

Central axle, and wheel revolves around the axle

Force magnified when applied farther from axle

Example of Wheel and Axle

• Pirate ship steering wheel

• Car driving wheel

Inclined Plane

Surface with one end higher than other

• Provides a way to lift a weight that is too heavy to lift directly

• less force but the object must be moved over a longer distance

Inclined plane examples

• Slide board for transfer

• Using a ramp to load a piano onto a truck