Forces/ Joint Reaction Forces
Define a force and recite Newton's 2nd law
Force is a push/pull that initiates, modifies, or stops a movement
Newton's 2nd law is F=ma.
Where is the center of mass of the body?
Anterior to S2
Draw the 3 different types of levers?
1st class: EF then fulcrum then IF
2nd class: fulcrum, EF, IF
3rd class: fulcrum, IR, EF
What are the 2 types of internal forces? Provide an anatomical example of both.
Active forces are generated by muscle.
Passive forces provide tension when stretches. Ex include connective tissues, ligaments and joint capsules.
If a person raises their arms above their head, where does their COM move to?
Superior
Why does the body have mostly 3rd class levers?
It gives us ROM and speed to complete functional tasks.
What is the most common external force that acts on the body?
Gravity
What happens when our COM moves outside of our bass of support?
We will fall down....ouch! Unless we move our body in a way to get our COM back into the bass of support.
Define mechanical advantage and what type can be found in each class of levers.
Mechanical advantage is the ratio of Ima to Ema.
1st class can be either =1, >1, <1
2nd class is >1
3rd class is <1
Describe a joint reaction force (JRF) and why they are important.
A JRF is a force that exists at a joint, developed in reaction to the net effect of internal and external forces.
JRF prevents segment translation to create a potential for rotation at joint.
True or False. Torque is generated if the external or internal force is applied directly at the axis of rotation.
False. There must be a moment arm in order to create the rotational direction of the force.
You are bicep curling a 45lb dumbbell in the GTC, your forearm length is 40cm, and your bicep inserts 10cm from your elbow. How many pounds of force does your bicep has to exert in order for you to curl the dumbbell?
Over 180lbs of force!!
Name 3 ways we as therapists can decrease JRF's to decrease pain?
Decrease external forces like making a purse lighter; water therapy, using a cane or walker
Describe how we could reduce the JRF of the tibiofemoral joint when doing a leg extension with a cuff weight.
Since we are not able to change the moment arm of a muscle insertion, we must change the EF or Ema. This can be changing the weight on the machine or putting the cuff weight closer to the knee.
Create a 1st class lever, then describe what mechanical advantage it has and how to place it into static equilibrium.
You can use items in the classroom or people.
This will vary. Up to teachers transgressions.