Normal Mobility

Mobility Defined

The ability to independently and safely move oneself from one place to another. It includes rolling, sit to stand, walk, run, etc..

Mobility according to the ICF

• Activity and Participation

• Body structure and function (Gait pattern)

Essential requirements of Gait

• Progression: Includes ability to initiate and terminate movement

• Postural control: Stability

• Adaptation: Ability to maintain progression/postural control while:

  • Avoiding obstacles

  • Anticipate and react to changes

  • Adaptation is what qualifies mobility in the activities and participation section of the ICF

Note: These 3 requirements cause Energy Efficiency with Minimal System Stress

Normal Velocity

1.46 m/sec

Normal Candence

90 -120 steps/min

Normal Step and Stride length

• Step: 28in

• Stride: 56 inc

Gait changes with slow walking

• Stance time increases

• Swing time remains constant

• Variability Increases

• Increased medio-lateral COM displacement

Goals of Stance Phase

1. Stabilizing the limb for weight acceptance

2. Shock absorption

3. Propulsion

Goals of Swing Phase

1. Reposition the limb

2. Clearing the ground

Braking forces

Why is gait so smooth?

Excellent mechanical transfer of gravitational and kinetic forces

Brain regions that contribute to gait

▪ SMA

▪ Medial primary sensorimotor areas

▪ Striatum

▪ Cerebellum

▪ Visual cortex and visual processing centers

▪ Brain stem

▪ With gait speed increase: increased prefrontal and premotor cortex activity

What happens when a cat is spinalized?

The cat was still able to walk due to central program generators

• CPGs: Dedicated networks of nerve cells that generate

  movements and that contain the information that

  is necessary to activate different motor neurons in

  the appropriate sequence and intensity to

  generate motor patterns. They are innate but can be adapted and

  perfected with experiences

Role of CPG

• Neural networks within the brainstem and spinal cord

• Produce specific, rhythmic movements

  • without conscious effort

  • without peripheral afferent feedback

• Brainstem examples: Chewing, breathing, swallowing

• SC example: Locomotion

CPG 2- Level Model

• Rhythm generator

  • Regulation of gait speed (step-cycle periods and phase durations)

• Pattern formation

  • Level of motor neuron activity

  • Has its own independent mesencephalic locomotor region input

Note: Although a key element that characterizes CPG is the capacity to cause movement without sensation: CPG’s are strongly influenced by central and peripheral information. Circuits exist at birth but final organization is dependent on experiences provided to the system

Locomotion after a spinal cord injury

▪ No descending influences

▪ No contact with the cerebellum

▪ External, afferent information is needed to generate movement

▪ Gait without descending influences even with stimulation will not be smooth: caricature gait

▪ Ideas: treadmill training, electrical stimulation, robotics

2 key reflexes in gait

• Stretch reflex: involved in extreme ranges of motion

• Extensor thrust: Facilitates the extensor muscles of the LE during weight bearing

Role of the Mesencephalic locomotor region (Brainstem) in gait

• Descending control of gait

• Activates the medial reticular formation

• Reticular formation activates the spinal locomotor system

Role of the cerebellum in Gait

• Automatic aspects of gait control

• Adjusts gait in novel contexts and when visual guidance is critical

Input: Somatosensory, visual and vestibular

Output: Reticular formation in the brainstem

Role of the basal ganglia in gait

▪ Maintains appropriate postural muscle tone

▪ Modulates rhythmic stepping movement

▪ Initiates locomotion

▪ Cognitive component

▪ Attention to task

Role of Posterior parietal cortex and posterior temporal cortex in gait

• Help visual recognition of objects and events from different viewpoints and process to move efficiently in space

• These and the superior colliculus are involved in orienting to novel stimuli in the visual field

• Hippocampus codes topographical information, parietal cortex codes into 3-D metrics

Role of supplementary motor area in gait

• Connections to the reticular formation

• Believed to assist with postural control during gait

• Planning and programming of locomotion with the premotor cortex

Muscle and Non-muscle contributions

• Muscle contributions: use of concentric and eccentric control

• Non- muscular contributions: torque - Passive extensor torques that occur during gait. Muscles are often counteracting these passive., non-muscular forces

Two critical things to consider about adaptation

1. Reactive strategies for modifying gait

2. Pro-active strategies for modifying gait

Note: Without intact sensory systems:

▪ ADAPTATION will be impacted

• Loss of appropriate reactive strategies

• Less efficiency with movement

Somatosensory system

▪ 1. Contributes to appropriate stepping frequency

▪ 2. Strongly influences inter-limb coordination

▪ 3. Joint receptors and muscle spindle afferents play a role in normal locomotion

▪ 4. Influence of cutaneous information assists with obstacle navigation and postural control (reactive strategies), even at the CPG level

At what level does somatosensation affects gait?

At the reflex level

Role of Visual system in gait

1. Helps us determine our speed (visual flow)

2. Gives cues to adjust body to maintain HAT upright against gravity

3. Avoid objects

4. Prediction

Piloting strategy

A mental representation of the spatial environment = topological information + metric information.

Visual system- inclines

UP:

▪ Increase in step length

▪ Increased muscle activity

▪ Reduced cadence

DOWN

▪ Decreased in step length

▪ Increased cadence

Turning Strategies

Depends on which foot is in front and which way you are turning.

▪ Step turns

▪ Spin turns

Role of vestibular system in gait

• Head must be stabilized during locomotion

• Head movements are independent from the movements of the trunk

• Eyes will move to keep targets in the fovea as part of the VOR – allows for steady vision during gait.

Cognition ad gait

• Dual-task is harder when obstacles are in the way

• Dual-task will also slow down the transition from walking to running’

Posture/locomotor skill vs cognitive skills

Initiation of Gait

• It is more than a controlled fall

• Swing limb will push onto the stance limn (both limbs will need to bear weight)

• Steady velocity is reached within 1-3 steps

What defines running?

Both feet are off the ground. A.K.A “Flight” or “Float”

Walk vs Run

Running causes

• Increased velocity

• Increased GRF

• Stance to swing ration 40:60

• Increased ROM at all joints

• Increased Eccentric control

• Change in initial contact of foot depending on speed (no heel strike)

• No double limb stance

• Decreased BOS

• Decreased COG

Stair walking requirements

• Progression - Muscle Forces

• Stability - Control the COM with a changing BOS

• Adaptation: Different heights, carpet, poor lighting etc

Stance/swing = 64%:36%

Stair walking- Ascent

• Stance

  • Weight acceptance: Front of foot

  • Pull-up: 2x the force to step up

  • Forward continuance: Most unstable as the contralateral toe lifts off- MOST LIKELY TO FALL HERE

• Swing

  • 1. Foot clearance and appropriate placement

  • 2. Tibialis anterior df the foot and hamstrings flex the knee

  • 3. Rectus femoris eccentric control at midswing for

  • 4. Hip flexion brings thigh up

  • 5. Foot placement controlled by hip extension and ankle df

Stair walking - Descent

Stance

• 1. Weight acceptance

  • Energy absorption

    • GRFs are 2x body weight

    • Gastrocnemius activation

• 2. Forwards continuance

• 3. Controlled- lowering

  • Primarily quadriceps muscle and some eccentric contraction of the soleus

Swing

• 1. Pull through - Hip flexors

• 2. Preparation for foot placement

  • Midswing, extension dominates at all 3 joints

  • Contact made first with lateral border of foot with tibialis anterior and gastrocnemius activity prior to contact

Sensory cues that can “Make or break” stair walking skills

Vision can alter ability for foot clearance and placement which are critical to safe movement strategies on the stairs

Transfer tasks- What should we be aware of?

▪ 1. Essential characteristics of the task you are asking of them

▪ 2. Sensory and motor strategies that normal individuals typically use to accomplish the task

▪ 3. Adaptations required for changing environmental characteristics

▪ 4. What impairments are hindering the patient from completing the task

3 essentail task requirements for transfers

1. Progression

2. Postural control (Stability)

3. Adaptability

They still aply to transfers and rolling

Sit to stand order of events

• Pre-Phase: scoot forward in chair

• Phase 1: forward lean of the trunk (flex at hips)

• Phase 2: buttocks leaves seat – critical event where the body is unstable

• Phase 3: extension phase when hip and knee extend to get the body vertical

• Phase 4: stabilization phase once upright

What environmental things can be altered to assist with this transition?

Order of muscle activation in sit to stand

1. Erector spinae

2. Rectus femoris

3. Vastus mediales

4. Biceps femoris

5. Gluteus MAc

6. Rectus abdominus

Analyzing supine to stand

• Analyzed by UE, LE, axial (trunk and head)

Rising from a bed

Strategies for rising from bed are highly variable:

▪ Still requires: progression, postural control (stability), adaptation

Rolling

Variable patterns are used. Essential features of the most common patterns:

▪ the head must come off the surface