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 mnnDnKU 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 1 st triceps 2 nd brachioradialis 3 rd 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 insufficiency- muscle has shortened as much as possible  Passive insufficiency- muscle 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?