Gravity & BOS

Question 1

Where does the COG lie in a non-uniform object?

Answer 1

Closest to the area with the most mass

Question 2

Where is the COG in humans?

Answer 2

6 inches from the pubis symphysis (around the belly button)

Question 3

Where is the COG located in women, when compared to men?

Answer 3

COG is lower in women than men

Question 4

In terms of COG & BOS, when is someone most stable?

Answer 4

When COG is over BOS

Question 5

Can the COG change with movement? What causes it to change?

Answer 5

Yes. Changes according to the mass and where it’s moving

Question 6

Humans move in between stability and mobility. Good balance allows us to _______ easily. Poor balance will cause us to ______.

Answer 6

Transition Fall

Question 7

Where is the COG in uniform objects? (i.e. balls or cubes)

Answer 7

In the exact center; part where all 3 planes meet

Question 8

How do adaptive device changes influence COG?

Answer 8

Causes the COG to move in the direction where the mass has increased

Question 9

What is the benefit of a lower COG height?

Answer 9

More stability

Question 10

How can we lower COG height?

Answer 10

Widen stance or BOS

Question 11

What is a COG projection?

Answer 11

Where the COG is going to go when we move (i.e. sit to stand)

Question 12

What happens when the COG projection falls outside of our BOS?

Answer 12

Lose our balance

Question 13

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?

Answer 13

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)

Question 14

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?

Answer 14

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)

Question 16

What is the hallmark of safe transfers?

Answer 16

Imagine where the person is going to go & make it as safe as possible

Question 17

In transfers & transitional BOS what should we do with the person’s body position to make sure they have a stable BOS?

Answer 17

Make sure the feet are directly under the new COG

Question 18

What should the therapist’s position be during transfers?

Answer 18

Bent knees, straight back, COG over BOS, close to the patient Ensure their own stability by not leaning too far forward or back

Question 19

Describe the relationship between COG and BOS in reclining wheelchairs

Answer 19

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)

Question 20

What is a “Tilt in Space” wheelchair? What is it used for?

Answer 20

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

Question 21

Where does the COG lie for a person seated in a wheelchair?

Answer 21

Forward and slightly higher

Question 22

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?

Answer 22

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

Question 23

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?

Answer 23

Front of chair can tip up (dangerous) Temporary fix: weights on footrest Long term fix: rear axel extender (attach to rear wheels) Anti-tippers

Question 24

What does a rear wheel extender do to the BOS & COG?

Answer 24

Extends BOS and causes the COG to move more towards the center

Question 25

What is rear-wheel camber?

Answer 25

The bottom of the wheelchair rims are further apart than the top of the rims Looks like this: / \

Question 26

Why is a rear-wheel camber beneficial?

Answer 26

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!