Motor Control 5

Question 1

What is Equilibrium?

Answer 1

If the sum of forces and moments acting on the system is zero (no net forces or moments)

Question 2

What is Stability?

Answer 2

The resilience to change in response to a perturbation

Question 3

What is stability in terms of potential energy?

Answer 3

If perturbation leads to an increase in potential energy, the system is more stable. If Perturbation leads to a decrease in potential energy, the system is less stable

Question 4

What is the base of support?

Answer 4

The area of support surface defined by straight lines drawn between the points of contact between the object and the surface

Question 5

What is the Centre of Pressure?

Answer 5

The point where resultant ground reaction force is applied

Question 6

What are the characteristics of the CoP?

Answer 6

• CoP is always within the base of support.
• CoP isn’t necessarily at a contact point (E.g. CoP between your feet)
• When static, CoP is directly beneath the CoG

Question 7

What is an inverted (compound) pendulum?

Answer 7

The model used to represent your body when balancing; a series of jointed segments that can rotate relative to eachother

Question 8

What is the element in the inverted compound pendulum that allows it to not collapse to the ground in quiet standing?

Answer 8

Muscles creating torques at each joint

Question 9

What is the ankle strategy of balancing?

Answer 9

Intermittent muscle activity at the ankle, mostly typical of quiet standing

Question 10

What is the hip strategy of balancing?

Answer 10

Based on adjustments made at multiple joints (especially the hip) mostly typical of larger perturbations

Question 11

What are Sway factors?

Answer 11

A variety of factors that can affect type and amount of sway in quiet standing

Question 12

What are the main categories of sway factors?

Answer 12

• Physical characteristics (e.g. age, fatigue)
• Body posture (e.g. feet position)
• Support surface (hardness, friction)
• Availability of sensory feedback

Question 13

Apart from visual, vestibular and proprioceptive feedback, what are the other strategies to improve postural stability?

Answer 13

-Cutaneous vibrations, light touch

Question 14

What are the two main types of activation strategies that occur, depending on perturbation characteristics (e.g. magnitude, speed)

Answer 14

Stereotyped activation patterns (distal to proximal)

Muscle Synergies