Gravity & BOS Flashcards
Where does the COG lie in a non-uniform object?
Closest to the area with the most mass
Where is the COG in humans?
6 inches from the pubis symphysis (around the belly button)
Where is the COG located in women, when compared to men?
COG is lower in women than men
In terms of COG & BOS, when is someone most stable?
When COG is over BOS
Can the COG change with movement? What causes it to change?
Yes. Changes according to the mass and where it’s moving
Humans move in between stability and mobility. Good balance allows us to _______ easily. Poor balance will cause us to ______.
Transition Fall
Where is the COG in uniform objects? (i.e. balls or cubes)
In the exact center; part where all 3 planes meet
How do adaptive device changes influence COG?
Causes the COG to move in the direction where the mass has increased
What is the benefit of a lower COG height?
More stability
How can we lower COG height?
Widen stance or BOS
What is a COG projection?
Where the COG is going to go when we move (i.e. sit to stand)
What happens when the COG projection falls outside of our BOS?
Lose our balance
With spinal cord injuries, what body position is used to achieve a larger BOS? Describe the position of the legs. Why is this position used?
Long sit Legs are extended out in front Provides more stability. The person uses the upper body to maintain COG over BOS (flex trunk forward, use head)
Case Study: Iris’ MS affects her sensation, response to weight bearing, and righting reactions. This compromises her ability to reach overhead cabinets. When Iris moves her R hand over her head and forward to reach into the cabinet, where does her COG move? What will happen if she continues to move in this way? What should she do to prevent this?
upward & forward COG will move outside of her BOS and will be at risk for falling (condition of instability) Prevention: use left hand to balance on the counter, long handled reacher, rearrange cabinets (also conserves energy)
What is the hallmark of safe transfers?
Imagine where the person is going to go & make it as safe as possible
In transfers & transitional BOS what should we do with the person’s body position to make sure they have a stable BOS?
Make sure the feet are directly under the new COG
What should the therapist’s position be during transfers?
Bent knees, straight back, COG over BOS, close to the patient Ensure their own stability by not leaning too far forward or back
Describe the relationship between COG and BOS in reclining wheelchairs
WCs normally have a large BOS (very stable) If the chair is reclined too far, the COG moves backwards & the front wheels come off the floor (no longer stable)
What is a “Tilt in Space” wheelchair? What is it used for?
Reclining wheelchair, but the chair slides forward over the BOS so there is no risk for falling Used for spinal cord injuries, quadriplegics Important for pressure relief
Where does the COG lie for a person seated in a wheelchair?
Forward and slightly higher
Where does the COG lie in a person with an amputation that is seated in a wheelchair? Why does it move? What are they at increased risk for?
COG moves backwards because the counter balance from the weight of the leg is not there - Loss of anterior mass, COG moves backward Increased risk for falling backwards
What can happen if you push a person with an amputation in a wheelchair too quickly? How can we bring the COG forward & increase the BOS?
Front of chair can tip up (dangerous) Temporary fix: weights on footrest Long term fix: rear axel extender (attach to rear wheels) Anti-tippers
What does a rear wheel extender do to the BOS & COG?
Extends BOS and causes the COG to move more towards the center
What is rear-wheel camber?
The bottom of the wheelchair rims are further apart than the top of the rims Looks like this: / \
Why is a rear-wheel camber beneficial?
Makes chair easier to maneuver Shoulders are in a more relaxed position (less shoulder ABD & scapular elevation) Creates a wider BOS (more stability) More lateral stability + greater maneuverability = good for sports!
