lecture 2

Question 1

why should we study balance?

Answer 1

balance serves as a platform to support and facilitate volitional movements: goal-directed, episodic, rhythmical.

Question 2

what is mobility?

Answer 2

the ability to move independently and safely from one place to another

Question 3

how does balance affect mobility?

Answer 3

balance affects locomotion. Poor locomotion affects independent and safe movement

Question 4

what are the discussed consequences of mobility dysfunction?

Answer 4

1. Physical and social activity restrictions.
2. Loss of independence.
3. Reduced quality of life.
4. falls.

Question 5

what is a fall?

Answer 5

unplanned, unexpected contact with a supporting surface

Question 6

what is postural control

Answer 6

Ability to control the body’s position in space to maintain stability and orientation

Question 7

define postural orientation

Answer 7

• Alignment of body parts and body orientation with respect to the environment.
• Commonly oriented relative to gravity in daily life.

Question 8

what are the 3 coordinate systems for postural orientation

Answer 8

1. egocentric
2. exocentric
3. geocentric

Question 9

define egocentric

Answer 9

Relative position of body parts to one another.

Question 10

define exocentric

Answer 10

Relative position of body parts to the environment.

Question 11

define geocentric

Answer 11

Relative position of body parts to the gravitational field

Question 12

why is postural orientation important

Answer 12

Good postural orientation minimizes muscle activity needed to counteract gravity

Question 13

what are anti gravity muscles?

Answer 13

muscles that are tonically active when maintaining posture

Question 14

what is postural tone

Answer 14

level of anti gravity muscle activity

Question 15

what are some causes of poor postural orientation?

Answer 15

1. musculoskeletal deficits (e.g. osteoporosis)
2. neurological deficits (e.g., stroke, Parkinson’s).

Question 16

what is postural stability

Answer 16

process that controls the body’s center of mass (COM) with respect to its base of support (BOS)

Question 17

how is balance related to postural stability?

Answer 17

Balance is the process of maintaining postural stability

Question 18

define center of mass

Answer 18

• COM is the point equivalent of total body mass in a global reference system.
• if multi segmented, the total COM
  is the weighted average of the COM of each body segment

Question 19

what happens to COM in uniform gravity?

Answer 19

COM = center of gravity (COG)

Question 20

define line of gravity

Answer 20

the vertical projection of COM on the ground

Question 21

define base of support (BOS)

Answer 21

the area enclosed by the outermost edges of supporting structures
that contact the environment and thereby allows ground reaction forces
to be generated

Question 22

how does the relationship between BOS and COM affect postural stability?

Answer 22

As long as the COM stays within the BOS, postural stability is maintained

Question 23

what is static equillibrium?

Answer 23

• when all opposing forces acting on the body are equal so that the body rests in an intended position
• COM must lie within BOS

Question 24

what are the 3 types of static equillibrium?

Answer 24

1. stable
2. unstable
3. neutral

Question 25

what is stable static equillibrium?

Answer 25

After a small force is applied, the object/body will return to its original equilibrium position

Question 26

what is unstable static equillibrium

Answer 26

After a small force is applied, the object/body will
not return to its original equilibrium
position and moves to a new equilibrium position

Question 27

define neutral static equillibrium

Answer 27

Even with a large force applied, the object will not change equilibrium position

Question 28

why is balance control difficult for humans

Answer 28

• 2/3s of bodyweight is located 2/3 of height above ground
• must maintain COM with large moment arm within small BOS

Question 29

what are two ways to make balance easier for humans?

Answer 29

• wider stance (larger BOS)
• lower stance (allows more angular displacement without exceeding BOS)