8.3 Steady State Balance

Question 1

What is steady-state balance?

Answer 1

The ability to control the center of mass relative to the base of support under predictable, unchanging conditions.

Question 2

Why is “static balance” sometimes misleading when describing steady-state balance?

Answer 2

Because even in quiet stance, there is continuous small postural sway.

Question 3

What is optimal alignment?

Answer 3

The body position that allows maintenance with the least energy expenditure.

Question 4

Where does the line of gravity pass in ideal standing alignment?

Answer 4

Through the mastoid process, in front of the shoulders, slightly behind the hip joints, in front of the center of the knees, and just in front of the ankles.

Question 5

Which muscles are active in maintaining ideal standing posture?

Answer 5

Erector spinae, iliopsoas, glute medius, gastrocnemius, and tibialis anterior.

Question 6

What two factors contribute to steady-state balance?

Answer 6

Muscle tone and postural tone.

Question 7

What three main factors contribute to background muscle tone in quiet stance?

Answer 7

Muscle stiffness, background neural muscle tone, and postural tone.

Question 8

How is muscle tone tested clinically?

Answer 8

By passively flexing and extending a relaxed limb and feeling for resistance.

Question 9

What are neural and non-neural mechanisms that contribute to muscle tone?

Answer 9

Non-neural: free calcium causing cross-bridge cycling; Neural: stretch reflexes resisting muscle lengthening.

Question 10

What is postural tone?

Answer 10

Activation of anti-gravity muscles to counteract gravity during quiet stance.

Question 11

Which muscles are active during quiet stance?

Answer 11

Soleus, gastrocnemius, tibialis anterior, glute medius, tensor fascia latae, iliopsoas, thoracic extensors, and intermittent abdominals.

Question 12

What two movement strategies are used to maintain steady-state balance?

Answer 12

Ankle strategy and hip strategy.

Question 13

Describe the ankle strategy.

Answer 13

The leg and trunk move in phase around the ankle joint to control balance.

Question 14

Describe the hip strategy.

Answer 14

The leg and trunk move out of phase, with larger hip motion and higher sway frequencies.

Question 15

What sensory systems contribute to steady-state balance?

Answer 15

Visual, somatosensory, and vestibular systems.

Question 16

What information does vision provide for postural control?

Answer 16

Head position, body motion relative to the environment, and vertical orientation.

Question 17

What is an example of visual misinterpretation during postural control?

Answer 17

Feeling like you are moving when a car next to you moves at a stoplight.

Question 18

How does vision affect sway amplitude?

Answer 18

Sway increases with eyes closed compared to eyes open.

Question 19

What is the Romberg quotient?

Answer 19

The ratio of body sway with eyes closed to sway with eyes open; used clinically to assess stability.

Question 20

What information do somatosensory receptors provide?

Answer 20

Position and motion of the body with respect to the support surface.

Question 21

When are somatosensory inputs less reliable?

Answer 21

When standing on unstable or moving surfaces like a boat or ramp.

Question 22

How can reduced somatosensory input affect balance?

Answer 22

It increases center of pressure motion during quiet stance.

Question 23

What does the light touch experiment demonstrate?

Answer 23

Light touch alone (without support) reduces body sway by providing somatosensory orientation cues.

Question 24

What does the vestibular system provide information about?

Answer 24

Head position and movement relative to gravity and inertial forces.

Question 25

Why can the vestibular system be inaccurate by itself?

Answer 25

It cannot distinguish between head motion alone and combined head-trunk motion.

Question 26

How do sensory systems work together for balance?

Answer 26

The CNS integrates visual, vestibular, and somatosensory input to maintain postural control.

Question 27

What is sensory reweighting?

Answer 27

The CNS adjusting the importance of sensory inputs depending on environmental conditions.

Question 28

What happens when visual input is removed (eyes closed)?

Answer 28

Body sway increases slightly, but balance can be maintained using vestibular and somatosensory cues.

Question 29

What happens when somatosensory input is inaccurate (e.g., moving platform)?

Answer 29

Body sway increases further, requiring greater reliance on vestibular and visual cues.

Question 30

What condition results in the most body sway?

Answer 30

When both visual and somatosensory inputs are inaccurate, leaving only vestibular input available.

Question 31

How does the CNS adapt when learning a new motor skill?

Answer 31

Initially increases weighting of visual input, then decreases visual reliance as the task becomes automatic.