Lecture 11: Balance and Stability Flashcards
Equilibrium
All forces and torques add to ZERO
Static equilibrium
NO acceleration (isometric position)
Dynamic equilibrium
There is acceleration but everything is equal to zero
W + 2F - m x a = 0
Inertial Forces
act to oppose any accelerations of the centre of mass
Ex. runner who is turning to his left will feel the inertial force downward and to his right
- opposite of the acceleration of his centre of mass
Equilibrium and stability
Equilibrium has NOTHING to do with stability
Equilibrium means adding up to zero (you are always in equilibrium)
Stability
How close the system is to “wiping out”
- wiping out: accelerating at a magnitude or direction that you don’t want
Often related to the size of the base of support
Base of support
region between edges of the points of contact
Larger region = more stable system
As long as weight vector goes through base of support, then the object is stable
Is walking stable?
Walking is BOTH stable and unstable
- when you lift foot, you become unstable
- uses lack of stability to move forward
- go from static stability to instability and back to static stability
Posture control
Posture is maintaining upright position
At ankles, knees, hips and spine, your EXTENSOR muscles maintain posture (anti-gravity muscles)
Anti-gravity muscles
Maintain upright position
EXTENSOR muscle groups at ankles, knees, hips and spine
Fainting and posture
When you faint, the extensor muscle groups relax and “buckle” into flexion
Ankles dorsiflex, knees flex, hips flex and spine flexes forward all at the same time
Postural sway
You know where your centre of mass is via 4 systems:
- Pressure on soles of feet
- Proprioceptive system (jt. sense)
- Vision
- Vestibular system of inner ears
Testing Postural Stability
The 4 systems involved in postural sway can be independently tested during a tilt test
- Chilling feet = turns off pressure sensors of feet
- Local anesthetic/nerve blocks = turns off proprioceptive system/ jt sense
- Virtual reality or closing eyes = turns off vision
- Chilling or heating ear canal = turns off vestibular system of inner ears
Landing/Rapid Stop
When landing a jump, the body’s inertia makes it want to continue doing what it was doing in the air (Newton’s 1st Law)
How you manage the inertial force on landing determines if you lose control
Banked corners
Can help maintain stability during a turn
