locomotion

3 fundamental types of movement

  • ambulation: brainstem (subconscious adaptation) and SC (reflexive)

  • posture: brainstem

  • reach/grasp: cerebral cortex

locomotion vs. ambulation: locomotion is how we move our body through space in whichever way is most efficient vs ambulation is walking

3 motor control requirements of ambulation

  • progression: moving body/COM in desired direction

  • postural control: maintain appropriate posture and dynamic stability to generate movement in a meaningful way

  • adaptation: to meet goals of individual and demands of environment/task

motor control of ambulation: descending control

  • cerebral cortex

    • provides a goal

    • control of overall movement plan

    • lateral corticospinal tract: goal directed motor program

    • medial corticospinal tract: posture through neck & trunk

  • brainstem (descending tracts)

    • posture and gross limb movements

    • reticulospinal: adjusts strength of muscle contractions

    • lateral & medial vestibulospinal tracts

  • basal ganglia (modulator)

    • force, amplitude, coordination modulation

  • cerebellum (modulator)

    • timing, coordination, error correction

  • spinal cord

    • stepping pattern generators (reflexive patterns) in lumbosacral

  • sensory information

    • adapt motor output related to environmental conditions (afferent input)

descending input pathway

  • supraspinal input from the brain (descending control)→spinal cord→reflex and central pattern generator→effector muscles

  • afferent input contributes to reflex arc and continues up to the brain

stepping pattern generators

  • ipsilateral side: flexor activated=extensor inhibited; extensor activated=flexor inhibited

  • contralateral side: flexor activated on IL=flexor inhibited on CL; extensor activated on IL=extensor inhibited on CL

    • IL flexors activated=extensors activated on CL side

  • cycles of these 2 SPGs coordinated by signals in anterior commissure of spinal cord

  • basic rhythmicity of stepping is produced by neuronal circuits contained entirely within SC

  • afferent input is processed at SC: joint position during swing, loading response during stance (via GTO)

  • descending input helps modulate and refine SPG movement

  • descending command centers=plans for and adjusts movement (ex. vision): environment and timing

  • afferent input to SC=proprioception and loading—not necessarily relying on input to initiate gait

  • terminal stance facilitates the transition from stance to swing

gait initiation

  • COP moves posterior & lateral over swing limb: bilateral ankle strategy against backward sway (TA, quads)

  • COP shifts toward stance limb and forward: TA causes DF in stance ankle→pull shank over foot as body moves forward in preparation for toe off

  • steady state velocity reached within 1-3 steps

    • not seen consistently in children until 4-5 y/o

adaptation

  • SPGs are adaptable

  • spontaneous recovery of SPGs

  • experience dependent adaptive neuroplasticity of SPGs

  • low variability—not able to adapt to environment very well (stepping over/around objects)

  • can train/modify coordinated control

  • stairs

    • adapting to environment (steps)

    • requires feedforward (descending) and feedback (afferent) pathways for adaptation

    • SPG alone are not sufficient to produce stair climbing

    • movement patterns/strategies

      • step to pattern

      • reciprocal pattern

    • 2x greater forces and ROM needed compared to level ground walking

      • ascent: force generation is 2x> concentric quads/knee extension

      • descent: GRF=2x BW with WA on descent (quads, gastroc)

    • ascent phases

      • stance: WA, pull up, forward continuation

      • swing: foot clearance, foot placement

    • descent phases

      • stance: WA, forward continuation, controlled lowering

      • swing: leg pull-through, preparation for foot placement

development of ambulation

  • stepping patterns

    • present in newborns

    • disappears ~2 mo

    • reappears

    • assisted ambulation ~10 mo

    • progress to indep walking ~12 mo

  • infant stepping

    • increased hip flex, fwd trunk lean, co-contraction

    • forward and backward progression of knee, rapid COM progression, stagnant & vertical movement in COM, excessive foot clearance

  • adult stepping

    • normalization of hip flex/upright trunk posture

    • reciprocal pattern of muscle activation, linear pattern

  • healthy older adults >65 yo

    • slower speeds, decr stride length, vertical head movement smaller, lateral movement larger

    • aging or pathology?

      • fall risk: gait variability, changes in feedback/reactive control

      • cognitive factors

      • sensory impairments (vision, proprioception, vestibular)

      • decr muscle strength

    • studies show excs can improve amb fx in OAs

walking speed: functional vital sign

  • not a great measure of ability to walk

  • related to mortality rate

  • is pt likely to walk safely only at home b/c they walk slow, or are they likely to be more able to get around community in short distances or are they truly community ambulatory (requires greater gait velocity ex. crossing the street)

considerations with impairment of neurologic system

  • decreased automatic processing of ambulation: motor or sensory impairments

  • cognitive processing impairments (attention)

    • decreased capacity for appropriate attention to ambulation

    • decreased ability for appropriate selection of attention on tasks

  • effects on ambulation

    • decreased gait speed, increased DL support, decr stride length, incr variability—regardless of pathology, all can be expected with any neuro pathology