DPT 6140 Biomechanics Quiz 4 Kinetics Pt. 3

Levers

Levers

What requires at least two linear forces each acting at a distance from the pivot point or axis?

1) Muscle force/Effort (EF in drawings)

2) Moment arm for the muscle force/Effort (EA)

3) Resistance in the form of gravity/external force/load pulling on segment/system (RF)

4) Moment arm for the resistance (RA)

What are the 4 variables of simple levers?

First Class Lever

What type of lever is this?

- Two sides, at some distance from the axis

- The forces will attempt to cause rotation in opposite directions

- The forces are applied on opposite sides of the fulcrum or axis

Second class lever

What type of lever?

- The (external) resistance force/load is in between (muscle) effort force and axis

- Both forces act at a distance from the same side of the axis

- Strength lever

Third class lever

What type of lever?

- The (muscle) effort force is between the (external) resistance force/load and axis

- Fast (speed) lever

First class lever

What type of lever?

Second class lever

What type of lever?

third class lever

What type of lever?

first class lever

What type of lever?

second class lever

What type of lever?

third class lever

What type of lever?

Mechanical Advantage (MAd)

_______________ = Effort Arm (EA) /
Resistance Arm (RA)

advantage

If MAd > 1.0, the internal (muscle) force has the _______________. A small amount of force can overcome a larger amount of resistance

larger

If MAd < 1.0, a _____________ amount of internal force is needed to overcome a smaller resistance - or - a small amount of external resistance can overcome a larger amount of internal force

Mechanical disadvantage
- joints are at a disadvantage

- The further the therapist's hand is pushing from the axis the less of an advantage the patient has

Are your patient's Quadriceps and Deltoids at a mechanical advantage or disadvantage during knee extension/shoulder abduction manual muscle test?

Force couple

What are forces acting together to move an object around a pivot point?

third class lever

- HF = Hamstrings Force (EFFORT IS IN THE MIDDLE SO 3rd class)
REMEMBER:
1st - F (force in middle)
2nd - R (resistance in middle)
3rd - E (Effort in middle)

- G1 is gravity pulling on the straight leg
- W1 is an ankle weight added to the leg

What class lever?

third

Most joints are _______ class levers

Resistance

does not

does not

For 3 class levers:

- _____________ has advantage

- Segment/system weight DOES or DOES NOT change (RF)

- Moment arm for muscle at a given joint angle DOES or DOES NOT change

If want to have muscle (EF) work harder (create more force):
o↑ RA

If want to have muscle (EF) work less (decrease force):
o↓ RA

Only 2 variables left are EF (muscle force) and RA (moment arm for resistance RF)

If want to have muscle (EF) work harder (create more force):

↑ or ↓ RA

If want to have muscle (EF) work less (decrease force):

↑ or ↓ RA

Moment arm is longer in supine, muscles wont have to work as hard in standing compare to in supine.

Which would be easier?

static equilibrium

What is activity but no visible movement?

Gravity
Quad

For the knee in this position:

1) ________ should produce flexor moment

2) _______ should produce an extensor moment

Extensor

If system is in static equilibrium:

Flexor moment = __________ moment

(Force x Distance) = (Force x distance)

QLf = 352

Assuming:

GWbLf = 88 N (about 20 lbs)

MAGWbLf = 20 cm

MAQLf = 5 cm

QLf = ???

Inertia

What is the property of object that resists initiation or change of motion?

greater, greater

Inertia is proportionate to the mass of an object --> greater the mass, the _________ the inertia and the __________ force needed to overcome the inertia

Radius of gyration (r)

The distance between the center of mass and the axis of rotation?

Newton's 1st law
- Applies for both linear and angular velocity

What law of Inertia?

- Bodies at rest tend to stay at rest; bodies in motion tend to stay in motion unless either is acted upon by an external force (unbalanced force)

2nd law

- Increasing time to lessen the effect of stopping a force

- Using momentum to decrease the force required to accomplish the motion

What law of inertia?

- a force applied to an object at rest causes it to accelerate in the direction of the force.

- The acceleration for a body of constant mass is proportional of the resultant forces causing it and the change takes place in the direction in which the force acts.

acceleration

The ____________ is inversely proportional to the mass of the body

lesser

Looking at relationships of F, m, and acceleration, both in linear and angular applications --> With everything else equal, part with _________ mass will move when acted upon

Linear Moment/Force

_________ Moment/Force = M x A

Angular Moment/Force

_________ Moment/Force = I x a

third law: Action-reaction

What law of inertia?

- To every action, there is an equal and opposite reaction

Impulse

What is the combination of force and time that is what is required to change the momentum of a body?

work

If there is movement and displacement that occurs then mechanical __________ has been done.

mechanical

No ___________ work is done if there is no movement

Power

What is work done over time?

_________ developed through angular motion tends to be related to muscle performance

Positive Power

What is the rate of work done by muscles during concentric contractions?

When...
- Internal muscle forces over external force
- Considered as generation or acceleration

Negative Power

What is the rate of work accomplished by muscles undergoing eccentric contractions?

When...
- External load over internal muscle force
- Considered an absorption or deceleration

Application of Newton's 3rd law of motion

Which of Newton's laws is at work?

Pressure

What is defined as ratio of force and area on which the force is applied?

•Units: N/m2