Control of normal mobility Flashcards
What are the three things we need for successful locomotion
- Progression (Move between two points)
- Postural Control
- Adaptation
Explain the phases of Gait
Goal during Stance Gait
- Generate horizontal forces (progression)
- Generate vertical forces (postural control; keep us upright)
- Adapt (speed, direction, support surface)
Goals during Swing Gait
- Advance the swing leg (progression)
- Position the swing leg (postural control)
- Adapt (obstacle avoidance, support surface)
Velocity - Gait
Average horizontal speed of body over 1+ strides
Velocity = step length X step cadence
Ave. adult velocity = 1.46 m/sec (3.26 mi/hr)
Step Length - Gait
- Distance from one foot strike to the next contralateral foot strike
- Ave. adult step length = 76.3 cm (30.05 in.)
- Heel to Heel or Toe to Toe
Step Frequency (Cadence)
- Number of steps per unit time
- Ave. adult walking cadence = 1.9 steps/second (112.5 steps/min) – differs for running
Step Width - Gait
Distance between the feet (base of support)
Normal range = 2.5 – 12.5 cm
If you see negative step width values, what does that mean?
They are ataxic and have a scissoring gait
If you see a step width outside normal, what could this mean?
They don’t feel stable thus create a larger BOS
When we increase walking speed, ____ time becomes shorter
stance
What is the difference between walking and running?
Running has flight time, no double support.
What happens when we decrease walking speed?
- Stance time increases
- Swing slows
- Decreased efficency, more time in single leg stance
- More variability (some is too too much is bad)
- COM displacement increases in the ML
- Contributes to instability
Why is some variability in movement/gait good?
Allows us to adapt to different circumstances and spreads out tissue stress.
A healthy amount of variability leads to…
- Smooth movements
- More stable control of center of mass through space
- Also allows for one joints loss of motion to compensate for the other (Although over time may lead to too much stress and causes injury)
When walking movement looks the same but ____ of the hip change 72% throughout!
muscle forces
How is locomotion efficiency maintained?
- COM fluctuates in a sinusoidal fashion (transfer of energy, goes up and down, side to side, nice continuous motion)
- Smooth transfer of mechanical energy reduces metabolic cost
Without sensory feedback what happens to gait?
- Gait is slow and stereotyped
- Difficult to maintain balance and modify patterns
- Ataxia is often observed
How does vision contribute to gait?
Optic flow
* Helps determine speed
* Influences alignment of body to gravity & environment
Focal vision
* Navigation and obstacle negotiation (need to look directly at something to avoid it)
How does vestibular contribute to gait?
- Detect angle of head with respect to gravity
- During locomotion, gaze stabilization is important
- Vestibulo-ocular reflex (VOR) important for stabilizing vision (sends signals to muscles to allow vision to be stable while moving)
- Tend to maintain a head position that ensures efficient VOR
What contributions does the somatosensory system give to gait?
Muscle Spindles and GTOs
* Stretched iliopsoas (muscle spindles) reset the locomotor rhythm
* GTOs influence timing of locomotor rhythm & allow adjustment to load carriage
Walking across room, hierarchical system for gait. SC gives basic gait patterns, brain gives vetibular and cerebellar then cortex gives visual information. The higher the more complex.
Every step hip goes into extension, muscle spindle and SC create locomotor rhythm.
Central pattern generation: connection in SC when triggered create a basic gait pattern.
Ex: Cat spinal cord cut in thoracic stretch gets them to do general walk.
All reflect controlled. No sensory so no adaptations available. Applies to SC
GTOs influence it with SC
EX: Backpack leads to muscles preparing for load on back
What is the crossed extensor reflex?
- Stetch reflex that leads to withdraw due to plantar cutaneous pressure or pain
- Ex: Step on nail
Dorsal foot cutaneous reflexes
Dorsal foot stimulated in…
Early to mid swing -> flex the swing leg and extend the stance
Late Swing -> Extend the swing leg and flex the stance
Reflex modulation in SC based on stretch reflex of plantar flexors
During platform perturbations while walking what reactive strategy is used?
Same basic principles as postural control (ankle strategy, hip strategy, etc.)
During typical slippery surface while walking what reactive strategy is used?
- Shorter strides, lower contact velocities and reduced stance time
While walking on soft or hard surfaces what reactive strategy is used?
- Adjust leg stiffness (to maintain efficency)
- This is important for sports return to play (Ex: Soccer)
Anticipatory (Feedforward) Strategies for Gait
We use vision to:
* Identify potential destabilizing effects of a task
* Anticipate modifications needed based on experience and predictive ability
* We sample the ground ~10% of the time
* Vision sampling increases on uneven surfaces, when specific foot placement is required or hazard in path (Ex: Hiking)
Neural control of gait
- Hierarchial
- SC
– Central pattern generators aka CPG (simple synergies for gait)
– Reflexes (cutaneous and muscular) - Brainstem
– Mesencephalic locomotor region (initiation of gair and soem vestibular adjustment patterns)
– Medial reticular formation (influence on CPGs in spinal cord activation) - Cerebellum
– Error detection and correction
– Externally triggered initiation (Access to all types of sensory information
Basal Ganglia and Supplementary Motor Area)
– Internally triggered initiation
– Gait pattern control (pattern, velocity and amplitude) - Cortex (Vision)
– What (perception) - Ventral
Where (action) - Dorsal - Parietal Cortex
– 3D representation of space (Vision) - Frontal Cortex
– Transforms information into functional, adaptable, goal directed behavior - Hippocampus
– Memory of properties of environment
What requires more attention an obstacle avoidance while walking or recovery from external pertubations?
obstacle avoidance while walking
Gait Initiation Specifics
Initiation
* Relaxation of gastroc and soleus to enable “fall” forward
* Followed by tibialis anterior activation to pull
Shift in center of pressure
* Midway between feet, then lateral toward swing limb, and then to stance limb and forward
When is steady velocity in gait reached?
Steady velocity is reached within 1-3 steps
Gait Turning Strategies
Spin Turn
- Narrow base of support (spinning on plant foot)
Step Turn
- Wider base of support
- Better option for older patients
Terminating Gait
- 1-2 step response with a short ste to decelerate the COM
- Muscle activation: Tibialis anterior, soleus, biceps femoris, vastus lateralis, gluteus medius and erector spinae
- Challenging due to eccentric control
What is so challenging about eccentric control?
Muscle firing pattern
* More reliant on large fiber motor units = less force resolution
Possible mechanical challenges
* Failure of actin/myosin linkage results in unpredictable force generation
Requires more neural resources
* Bottom line – fMRI shows increased neural resources required to control eccentric contractions
When analyzing mobility what do we need to consider?
- Motion in desired direction (progression)
- Stability (postural control)
- Ability to adapt to changing task and environmental conditions (adaptation)
More falls occur when ____ the stairs
Descending
