Movement Science Week 10

Attentional demands

vary in function

-type of postural task and sensory context

-performance of secondary task not always detrimental to postural control

-important to assess balance under both single and duel task conditions

Steady-State Balance

- Body alignment can minimize effect of gravitational forces

- Muscle tone keeps body from collapsing in response to the pull of gravity (Intrinsic stiffness of muscles, background muscle tone, postural tone)

Muscle Tone

-Force with which a muscle resists being lengthened

-certain level of muscle tone is always present in conscious, relaxed people

-non neural contributions to muscle tone

-neural contributions to muscle tone

SSB movement strategies

-stability limits point at which a person will change the configuration of BOS to achieve flexibility

-not fixed boundaries; change according to task and characteristics of person and environment

-affected by position and velocity of COM at any given moment

Attentional resources

information processing resources required to complete a task

Dual-task interference

two tasks performed simultaneously; attentional resources may decrease in performance on one or more tasks

Spinal Contributions

-orientation component of postural control: tonic activation of extensor muscles for weight support

-directionally specific responses to perturbations present at spinal cord level

Brainstem contributions

-regulation of postural tone and automatic postural synergies

-nuclei contribute to restoration of equillibrium

-regulation of anticipatory postural control

Basal ganglia and cerebellar contributions

- cerebellum controls adaptation of postural responses

- basal ganglia control postural set, react to changing environment quickly

Alignment

-midline of mastoid process

-just in front of shoulder joints

-close to midline of the hip joints

-anterior to center of knee

-just infront of the ankle joint

Postural tone

-activity in antigravity postural muscles increases to counteract the gravity

-Sensory inputs from multiple systems are critical to postural tone

-trunk and limb muscle activation is critical to the maintenance of steady state balance when sitting in a quiet stance

AP stability

ankle, hip, change in support strategies

ML and multidirectional stability

alignment of body segments and muscles requires activation of forces at different joints and in different directions to recover stability

Refining and tuning muscle synergies

-Postural synergies not fixed, stereotypical reactions

-They are refined and tuned in response to changing demands in task and environment

-Adaptation: refining and tuning movements in response to task demands

Reactive balance control in sitting

-recovery of stability in seated position controlled similarly to that in stance

-individual muscles change their relative activation depending on direction of instability

Proactive balance control

CNS uses anticipatory processes in controlling action

-Critical to lower-extremity activites

-Postural activity anticipates voluntary movement

Optimal Postural control

-ability to maintain a vertical orientation in regard to gravity

-ability to maintain balance in presence of both internal and external challenges

Postural control

Controlling body's position in space for dual purposes of stability and orientation

Postural orientation

ability to maintain relationship between body segments and between body and environment for a task

Postural stability

ability to control the COM in relationship to the BOS

Center of mass

a point at the center of the total body mass

center of gravity

Vertical projection of the COM

Base of support

area of the body in contact with the support surface

Task constraints to postural control

Balance control: steady state, reactive, and proactive

-Feedback control: occurs in response to sensory feedback from an external perturbation: REACTIVE

-Feedforward control: anticipatory postural adjustments made in anticipation of a voluntary movement: ANTICIPATORY

Environmental constraints to postural control

-Changes in support surface

-differences in visual and surface conditions

-multiple tasks

SSB Visual contributions

-Position and motion of head with respect to surrounding objects

-reference for verticality

-info for steady-state postural control

SSB Somatosensory

-Provides CNS with position and motion info about the body with reference to support systems

-Reports info about the relationship of body segments to another

Task-dependent sensory reweighting

-CNS reweights sensory info under task changing conditions

-occurs during learning of new motor skills

Sensory inputs for reactive balance

- Visual information: gathered as person enters environment to form a map of environmental affordances

- Somatosensory inputs: controlling body sway when imbalance caused by rapid displacements of support surface

- Contribution of vestibular system: smaller than somatosensory inputs

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