Transcript Concepts of Physics

Concepts of Physics
A very, very simplified version
Why do we need physics?
Concepts give you a foundation of
knowledge for a ther. ex. Program
Use knowledge for stretching and
strengthening
Force
Form of energy that causes movement
and has direction and magnitude
Internal or external for body and creates push
or pull
Example: gravity
Newton’s Laws
https://www.youtube.com/watch?v=mn34
mnnDnKU
Basic Physics
Center of gravity- point of the body in
which weight is balanced
Generally around S2
Changes with
Gender
Children vs adults
Movement
Weight added
Stability & Fixation
Line of gravity- line running
vertically through the COG
Base of support- area between
and including objects points of
contact with supporting surface
Stable- when the line of gravity
falls within the base of support
Football lineman, riding a train,
manual muscle resistance
Fixation- state of stabilization in which
motion is restricted or prevented
Degree of stabilization optimal for efficient
muscle function
Occurs with active muscle contraction or
application of external force
• Keeps from substituting muscles (4 way theraband)
Levers
Contains a rigid bar and a fulcrum
Each of the 3 types has
Force arm (force point)
Resistance arm (resistance point)- distance
from fulcrum to resistance point
In body is the COG of the body part being moved
Adding weight moves COG
Fulcrum
Joint (bone is the bar)
First Class Lever
Fulcrum is located between the resistance
and the force.
Seesaw
What happens when one person moves closer?
Second Class Lever
Resistance point between fulcrum and
force
Always has a longer force arm
Wheelbarrow
Third Class Lever
Force between fulcrum and resistance
Inefficient due to force arm being shorter
than resistance arm
Levers
 1st triceps
 2nd brachioradialis
 3rd biceps
 Can increase or decrease forces produced,
speed of movement, range of movement
If one or more of these factors increases, the remaining
factors decrease.
 Conversely, if one or more decrease, the remaining
increase
Levers and Force
Torque
Ability of a force to cause rotational movement
Product of the fore and length of the force arm
Expressed in Newton-meters, foot-pounds,
inch-pounds
How this applies to Rehab
 Apply manual resistance to thigh during SLR vs
holding at ankle
At thigh: your torque is less
At ankle: your effort is less for the same torque
production because your lever arm is longer
 If a patient has hard time doing SLR vs gravity,
bend the knee to shorten the legs resistance
arm
 Torque changes throughout ROM
Line and Angle Of Pull
Line of pull- long axis of the muscle
Angle of pull- angle between long axis of
the bone (lever arm) and lone of pull of the
muscle
Why do we need to know this?
Avoiding limb positions that will exacerbate
problem
Dislocated shoulder avoid overhead or full ER
Angle of pull
To produce the max torque, joint must be
positioned so the muscle being worked
has 90 degree angle of pull on extremity
With free weights, max resistance occurs when
the pull of weight is perpendicular to the ground
regardless of position of extremity
Multi Joint Muscles
 When a muscle is
shortened, it will
affect all joints
crossed
Active insufficiencymuscle has shortened
as much as possible
Passive insufficiencymuscle elongated over
joint, antagonistic
muscle can’t shorten
anymore
 When a multi joint
muscle contracts,
should be elongated
at the stabilized,
unaffected joint
Ex: working HS during
knee flexion exercise
 Position Pt. sitting so
HS lengthened at hip
to allow better
contraction at the knee
• Prone: HS already
shortened
 HS already shortened
HS lengthened at hip
Summation Of Forces
Used during functional portion of rehab
Sequence of movements so that one
movement contributes to next to produce
desired outcome
Transfer of force will
fail if each joint not
correctly stabilized
Other Concepts
 Strength- ability to resist
or produce force
 Work- product of amount
of force (F) and the
distance (d) through
which the force is applied
 W= F x d
 Power- work per unit of
time (how fast work
produced
 P= Fd/t
 Energy
 Potential
 Kinetic
 Velocity- rate of change in
position
 Acceleration- rate in
which velocity changes
 Elasticity
 Stress and Strain
 Creep
 Friction
Try these
 1. sitting, perform shoulder flexion to 90 degrees
with #5 weight
Now put weight above the elbow
Which was easier
 2. Have partner lie supine, perform SLR, then
resist at mid thigh, knee, and ankle
Which was easier for clinician? Patient?
 3. Resist prone HS curl, seated HS curl
Which felt more HS concentrated?
 4. Standing bicep curl with weight, then supine.
Where was the hardest position in each?