Postural control - Task requirements: Feedback and feedforward mechanisms
Proactive balance control relies on feedforward (“open loop”) mechanisms
- Anticipatory postural adjustments (APAs) in advance of a voluntary movement that is potentially destabilizing
Reactive balance control relies on feedback (“closed loop”) mechanisms
- Corrective postural control strategies in response to detected sensory errors after external perturbation
Postural control
Controlling the body’s position in space for dual purposes of stability and orientation
Postural stability: ability to control COM in relationship to BOS
Postural orientation: ability to maintain appropriate relationship between body segments and between body and environment for a task
Stability and orientation requirements vary with task and environment
Postural control - Ankle strategy (small pertubations)
Forward sway: Activation of posterior musculature in a caudal to rostral pattern
- Ankle in trunk in phase
Backward sway: Activation of anterior musculature in a caudal to rostral pattern
- Ankle and trunk in phase
Postural control - Hip strategy (larger perturbations)
Forward sway: Activation of anterior musculature in a rostral to caudal pattern
- Ankle and trunk out of phase
Backward sway: Activation of posterior musculature in a rostral to caudal pattern
- Ankle and trunk out of phase
Postural control - Stepping strategy (COM outside BOS)
Change in support
Realign BOS under changing COM
Theories of sensory integration - Sensory weighting hypothesis
- Each sense provides unique contribution to postural control
- Postural control system can reweight sensory inputs to optimize stability in altered sensory environments
Gait and mobility - Motor systems
Essential requirements of gait:
- Progression: Basic locomotor pattern that produces and coordinates rhythmic patterns of muscle activation
- Postural control: Organization of multiple body systems to achieve orientation and stability (steady -state, reactive, proactive/anticipatory)
- Adaptation: Accomplishing progression and postural control within changing task and environmental demands (stop/start, change in direction, incline, etc)
Gait and mobility - Somatosensory system
Somatosensory feedback, especially from hip flexors in terminal stance, have a key role in progression by activation in the swing phase of gait
Joint receptors and muscle spindle afferents (from stretched hip flexors) influence rhythm-generating neurons and contribute to onset of swing phase
Gait and mobility - Motor systems: Control mechanisms
Continuous interaction between CPGs and descending signals
Higher centers contribute to locomotion through feedforward modulation of patterns in response to goals of individual and environmental demands
Nervous system takes into account non-neuromuscular forces in control of gait
Gait and mobility: Musculoskeletal contributions to gait
Both muscular and non-muscular forces generate gait dynamics
Clinical connection: Changes in passive properties of musculoskeletal system that occur with neuropathology or aging can influence gait
