Exam 3 Week 14/15 ppt 16 & 17: Balance: Perturbation & Response pt 1 & 2

Question 1

What happens as a response to purturbation?

Answer 1

• •When COM falls outside the BOS as a result of a sudden perturbation, postural compensatory strategies are needed to compensate for this imbalance or a fall will occur
• •Compensatory strategies include:
  
  1. –Controlling postural sway
  2. –Feedback control
  3. –Feedforward Anticipatory Control

Question 2

Response to Perturbation: Three types of compensatory strategies

Answer 2

•Compensatory strategies include:

1. –Controlling postural sway
2. –Feedback control
3. –Feedforward Anticipatory Control

Question 3

What are three responses to increasing magnitude of anteroposterior instability due to increasing amounts of perturbation?

(these are the three that Dr. Bringman taught us)

Answer 3

1. –Ankle strategy
2. –Hip strategy
3. –Stepping strategy

Question 4

When is the ankle stratagy effective?

Answer 4

When there are Small or low velocity perturbations producing small or slow deviations of the COM out of the BOS the situation can be easily Corrected for with the use of the the Ankle Strategy pattern

Question 5

Explain how the ankle strategy works:

Answer 5

•Ankle Strategy

1. –If the body sways forward the ankle goes into dorsiflexion
   
   • –Muscle action must pull the body back posteiroally
2. –If the body sways backward the ankle plantar flexes
   
   • –Muscle action needs to pull the body forward

Question 6

Explain the details of how the ankle strategy compensates for a perturbaiton that pushes the body forward:

Answer 6

1. –Sequence of muscle activation beginning with gastrocnemius
   
   • –Producing a plantar flexion at the ankle
   • –Occurs within 80 msec after perturbation
2. –Sequence of muscle activation continues with hamstring activation
   
   • –Occurs at about 100 msec after perturbation
3. –Sequence of muscle activation ends with activation of the paraspinals
   
   • –Occurs at about 120 msec following the perturbation

Question 7

Explain the details of how the ankle strategy compensates for a perturbaiton that pushes the body backwards:

Answer 7

1. –Sequence of muscle activation beginning with tibialis anterior
   
   • –Producing a dorsiflexion at the ankle
   • –Occurs at about 80 msec after perturbation
2. –Sequence of muscle activation continues with quadriceps femoris contraction
   
   • –Occurs at about 100 msec following perturbation
3. –Sequence of muscle activation ends with contraction of the abdominal muscles
   
   • –Occurs at about 120 msec following the perturbation

Question 8

Summarize the Ankle Stratagy

Answer 8

In summary where there is a small magnitude or slow velocity perturbation the ankle strategy is initiated. So when leaning forward produces a forward shift of the COM, which we have to correct by bringing the COM back over the BOS. This is done by sequential contraction of the gastrocnemius/soleus, hamstring and then paraspinals in sequence. When leaning backward produces a backward shift of the COM, which we have to correct by bringing the COM back forward over the BOS. This is done by sequential contraction of the tibialis anterior, quadriceps femoris and finally the abdomnals

Question 9

when is the hip stratagy effective?

Answer 9

• –Greater magnitude or higher velocity perturbations producing large or fast deviations of the COM out of the BOS
• –Corrected when the Hip Strategy pattern is initiate

When there is a Greater magnitude or higher velocity perturbations producing large or fast deviations of the COM out of the BOS and that are greater than can be handled by the ankle strategy, they are Corrected using the Hip Strategy pattern

Question 10

Explain the details of how the hip stratagy compensates for a perturbaiton that pushes the body forwards:

Answer 10

If the body sways forward & the COM goes forward, Muscle action must pull the COM back over the BOS.

1. –Sequence of muscle activation beginning with quadriceps femoris
   
   • –This produces a knee extension
   • –Occurs within 80-90 msec following the perturbation
2. –Sequence of muscle activation continues almost immediately by the abdominals
   
   • –Produces a hip flexion pulling the COM back over the feet (BOS)

Question 11

Explain the details of how the hip stratagy compensates for a perturbaiton that pushes the body backwards:

Answer 11

If the body sways backward & the COM moves backwards, Muscle action needs to pull the COM forward.

1. –Sequence of muscle activation beginning with hamstrings
   
   • –Produces knee flexion
   • –Occurs within about 80-90 msec after perturbation
2. –Sequence of muscle activation continues almost immediately by paraspinal activation
   
   • –This extends trunk pulling the COM back over the feet (BOS)

Question 12

Summarize the Hip Stratagy

Answer 12

In the Hip Strategy If the body sways forward & the COM goes forward and Muscle action must pull the COM back over the BOS The compensatory response is contraction of the quadriceps femoris producing a knee extension and contraction of the abdominals to push the COM backward. If the body sways backward & the COM goes backward and Muscle action must pull the COM forward over the BOS The compensatory response is contraction of the hamstrings producing a knee flexionand contraction of the paraspinals to push the COM forward.

Question 13

When is the Stepping Strategy effective?

Answer 13

• •If an even greater or higher velocity perturbations producing an even larger or faster deviation of the COM out of the BOS occur
• •Deviation may be so great that it cannot be compensated for by either the ankle or hip strategies
• •The person steps forward or backward to widen the base of support in a Stepping Strategy.

If an even greater or higher velocity perturbations producing an even larger or faster deviation of the COM out of the BOS occur, the Deviation may be so great that it cannot be compensated for by either the ankle or hip strategies. So the person steps forward or backward to widen the base of support in a Stepping Strategy.

Question 14

what can have a large effect upon which stratagy is selected to respond to a purturbation?

Answer 14

Environmental factors

Question 15

Explain Environmental Effects on response to perturbation:

Answer 15

•Environmental Effects

1. –Postural strategies adaptive to different environmental conditions
2. –On flat ground ankle strategy can be used for moderate perturbations
3. –If person standing on irregular or compliant surfaces, they have to move to higher level strategy sooner

Which strategy that is selected will depend upon Environmental factors. Postural strategies adaptive to different environmental conditions. For instance On flat ground ankle strategy can be used for moderate perturbations but If the person standing on irregular or compliant surfaces, they have to move to higher level strategy sooner

Question 16

Explain the body’s response to mediolateral perturbations:

Answer 16

• –Adaptation to mediolateral perturbations occurs at hip & trunk because of little movement in those directions at knee & ankle
• –Pattern of response begins with head/trunk followed by hip with head movement opposite to hip movement
• –Monoarticular muscle response occur before biarticular muscles are activated

In addition to the antero-posterior strability we have been discussion there are also issues of Mediolateral stability. Adaptation to mediolateral perturbations occurs at hip & trunk because of little movement in those directions at knee & ankle. Pattern of response begins with head/trunk followed by hip with head movement opposite to hip movement. Monoarticular muscle response occur before biarticular muscles are activated

Question 17

Explain the body’s response to multidirectional perturbations:

Answer 17

•Multidirectional Stability

• –Continuum of response patterns that control stability in the 360-degree continuum of possible perturbation directions
• –Each muscle can belong to more than one synergy or strategies
• –Within a synergy an individual muscle has a unique or fixed level of muscle activation for the different synergies

So a person must maintain Multidirectional Stability with a Continuum of response patterns that control stability in the 360-degree continuum of possible perturbation directions. Each muscle can belong to more than one synergy or strategies. Within a synergy an individual muscle has a unique or fixed level of muscle activation for the different synergies

Question 18

Chart of multidiretional stability with one pattern of muscle activation

(not really a question)

Answer 18

Chart of multidiretional stability with one pattern of muscle activation

(not really a question)

Question 19

How do subjects without neuroal pathology adapt to various perurbations or threats to balance?

Answer 19

•Adapting by applying different motor strategies

1. –Subjects without neural pathology can shift relatively quickly from one postural movement strategy to another
2. –Repeated exposure to a given postural task causes subjects to refine their response characteristics to optimize response efficiency

Humans will Adapt by applying different motor strategies. Subjects without neural pathology can shift relatively quickly from one postural movement strategy to another. Repeated exposure to a given postural task causes subjects to refine their response characteristics to optimize response efficiency. At the end of the bus ride the strategies and shift in strategies is well worked out so are initiated in a quicker and smoother way than at the beginning of the bus ride