NM CH 12

Trips: -Strategy used to maintain stability depends on when in the swing phase the trip occurs:

-Early swing=> elevation strategy -Mid swing=> varies; either strategy could be used -Late swing=> lowering strategy

Preferred step rates appear to be related to:

-Minimizing energy requirements per unit distance (meaning walk @ the speed that is best for you!!) -Using momentum (passive pendular properties that can be required @ higher or lower speeds)

Muscles in the swing limb do what?

-Not as much muscle activation as opposed to stance limb -muscle activity is largely confined to the beginning & end of the swing phase, since leg swings much like a jointed pendulum under the influence of gravity (so early on firing to get it going & toward end more firing to slow it down)

Vestibular System: -how do adults appear to stabilize head/gaze? -what is hypothesized during complex moments of postural control?

-Stabilizes head -by covarying the pitch (forward) rotation and vertical displacement of the head to give stability to the head in the sagittal plane -top-down theory=> in this mode, head mvmts are independent from trunk mvmts

Muscles in the stance limb do what?

-Support the body (postural control) -Propel it forward (progression)- in horizontal direction

CPG vs Adaptive Center Mvmts:

-crude mvmts -smooth, refined, adaptable mvmts

Vision: Visual flow helps:

-determine speed of locomotion (how fast we are walking) -influences alignment of body with reference to gravity & environment during walking g

Slips: -Muscle response patterns to balance threats occur: -What if their are multiple slips? How do we adjust?

-distal to proximal (wt arm mvmts used commonly) -adapt their strategy of recovery (YOUNG NORMAL PPL) by incorporating practice adjustments in subsequent trials ex: (walkingover icy side walk- first time have big slip response. Overtime, able to adapt and have smaller response to slip)

When is the gait cycle spent in double support?

-first & last 10% of stance phase

Heiarchy of postural & gait tasks based on attentional processing requirements from lowest level (least attention) to hight level (most attention)

-sitting -standing wt feet shoulder width apart -standing in tandem -walking -obstacle avoidance while walking -recovery from external perturbations

Somatosensory systems: -sensory info from limbs contributes to.. -What are very important, especially for onset of swing phase? what muscles is activated & how? -What can influence timing of the locomotor rhythm? how? -What else can influence Spinal PG? How? -What are integrated into the different phases of gait?

-to appropriate stepping frequency -Joint receptors and muscle spindle activity are important, especially for onset of swing phase (activated by stretched hip flexors). The muscle spindle afferents from hip flexors influence the rhythm-generating neurons by exciting hip flexor activity -GTO afferents from the leg extensors can also influence the timing of the locomotor rhythm by inhibiting flexor burst activity and promoting extensor activity. They may also provide a mechanism for automatically compensating for changes in loads carried by extensor muscles. (note GOT activity during locomotion is opposite to its activity when activated passively) -Cutaneous information also influences spinal pattern generators The response depends on the phase of gait when the cutaneous input is received Stretch reflexes are also modulated according to the phase of gait. -Automatic postural control

Stance Phase: Muscle Activation Patterns 1. What happens @ the initiation of stance phase? 2. Eccentric activation helps control what other muscles? 3. Postural stability during the stance phase involves activation of what? 4. Activation of the hip extensor muscles controls: 5. By mid stance, what muscles become PREDOMINANTLY INACTIVE?

1. -Knee flexion occurs= foot strike impact from heel contact to foot-flat stance -Eccentric activation of the knee extensors to control small knee flexion used to absorb the impact of foot strike 2. ankle DF to decelerate the foot on touchdown, opposing & slowing the PF that results from heel strike 3. activation of extensor muscles of the hip, knee & ankle 4. forward motion of the head, arm, & trunk segments 5. Quads & pre-tin muscles

Proactive Visual control 2 strategies:

1. Avoidance -Changing the placement of the foot -Increasing ground clearance to avoid an obstacle -Changing the direction of gait, when it is perceived that objects cannot be cleared -Stopping 2. Accomodation=long term modifications -Reducing step length when walking on an icy surface -Shifting the propulsive power from the ankle to hip and knee muscles when climbing stairs

Lesions & Impact on Descending Influences: So what if all that was intact was.... 1. SC 2. Decerebrate (Cerebellum; BS) 3. Decorticate (motor & visual cortex) 4. Completely Intact (no lesion)

1. Near normal inter/intralimb rhythmic activation patterns (have reflexes & rhythmic mvmts concurrently) 2. Improved coordination of activation patterns; weight support; active propulsion 3. dynamic stability; initiates reasonably normal goal-directed behavior in neonatally decorticate animals 4. Adaptable locomotor control systems to meet goals of animals in any environment

What are 3 essential requirements of locomotion? -these 3 requirements must be achieved with strategies that are:

1. Progression -Pattern that produces coordinated rhythmic patterns of muscle activation in the legs/trunk that successfully move the body to desired direction -requires ability to initiate & terminate locomotion as well as to guide toward endpoints that aren't always visible 2. Postural control -Ability to establish/maintain appropriate posture for locomotion & demand for dynamic stability 3. Ability to adapt -in order to meet goals of individual and demands of the environment -Energy efficient & effective in minimizing stress to the locomotor apparatus (AKA the body... if we have very weak quads, can hyperextend knee to compensate. THIS IS NOT THE BEST STRATEGY bc tears up knee)

How is normal equilibrium controlled during gait?

1. Reactive mode=> unexpected disturbances 2. Proactive mode=> anticipates potential disruptions to gait & to modify the way to sense & move in order to minimize the disruption (we know its coming.. ex: running up hill so we lean forward to help us get up hill)

Swing Phase: Muscle Activation Pattners 1. What is the goal? 2. During preswing, what muscles are used to accelerate knee into flexion? -what other muscles are activated to assist in forward acceleration? 3. What become active @ end of swing? Why? 4. What occurs @ the end of swing phase? What type of forces are these?

1. Reposition the limb for continued forward progression -accelerating the limb forward -making sure toe clears the ground 2. hip flexors & biceps femoris -concentric contraction of quads=> assist in FA of thigh in early swing phase 3. hamstrings=> help slow the forward rotation of the thigh 4. Knee extension=> passive nonmuscular forces

2 Level model (more recent model)

1. Rhythm Generator=> independently regulates gait speed 2. Pattern formation network=> independently regulates motor neuron activity -Basically regulates how fast firing is happening- how quickly are they alternating back & forth (flexible network for both sensory & descending control that 1CPG could not really do)

Phases of Gait: -what are each phases goals?

1. Stance/Support -generate horizontal forces against support surface (progression) -vertical forces to support body (Postural control) -adaptability=> flexibility in changes in speed/direction due to changes in the support surface 2. Swing -move swing leg forward (progression) -reposition limb in reparation for weight bearing (postural control)- for next stance -Adaptability=> flexibility to swing foot to avoid obstacles in its path & promote foot clearance

Proactive Strategies: 1. Foot Placement: 2. Step over or move around? 3. Experience affects avoidance strategy chosen? 4. look @ slide 51 to continue

1. Step length is increased when possible; The foot is placed inside rather than outside of the obstacle, as long as the foot does not need to cross the midline of the body 2. Decision related to object size as compared with the body size 3. Perceived fragility of an obstacle influences the amount of toe clearance with clearance being larger for the more fragile objects

Temporal & Distance factors affecting gait?

1. Velocity= average horizontal speed of the body measured over 1 or more strides -m/s; or either distance or mph -ex: 6MWT 2. Cadence= # of steps per unit of time -steps/minute 3. Step length= distance from 1 foot strike to the foot strike of the other foot 4. Stride length= distance covered from 1 heel strike to the next heel strike by the same foot

Mobility:

Ability to independently & safely move oneself from 1 place to another ex= walk, jump, etc

During Stance Phase, what is the primary strategy used to propel the body forward during locomotion? -Which theory is correct?

Active push off vs controlled roll off theories -APO= concentric contraction of the plantar flexors at the end of stance phase generates energy that is transferred to the trunk to provide support and forward progression (hip flexors provide pull-off; hip extensors give the body a "push from behind) -RO= forward progression is accomplished passively as the body moves forward as a result of momentum and inertia (the primary action of the plantar flexors is to decelerate tibia rotation and prevent knee flexion and the body rotates over the stance leg) BOTH!!!

Determinants of Gait Theory: Back in the day vs now

Back in the day= minimization of vertical COM motion is responsible for maximizing energy efficiency Today= smooth mechanical transfer of energies (1 legs to the other as we move thru swing phase) contributes to reducing metabolic cost of walking (more energy efficient)

Half Center Model: -CPG have... -Inhibitory connections btwn half-centers allow only: -How do you switch between extensor & flexors?

CPG responsible for alternating flexor & extensor movements -each limb separately controlled by its own CPG -2 groups of excitatory interneurons (half centers) for the flexor and extensor motor neurons -1 center to be active @ a time -interneurons fatigue quickly & run out of transmitters. So sends message & then fatigues which reduces excitation & allows other half center to take over (process just repeats)

What are "Kinematics of the gait cycle"

Coordinated movements of joints/segments (rolls/glides) of the body thru space -coordination allows for a smooth forward progression of the COM

Explain dynamic stability

Counteracting not only the forces of gravity but also other expected & unexpected forces -ex of unexpected forces= wind, crowds, etc

Reactive Strategies for Modifying Gait:

Humans adjust muscle stiffness according to the surface they are moving across 1. Somatosensory systems 2. Slips 3. Trips 4. Vision 5. Vestibular System 6. Proactive Strategies

Proactive Visual control of locomotion does not require : Proactive Visual Control can be used in:

Repeated exposure to a situation (never stepped over rock, can probaly do it. Use vision to help with this) Any environmental Setting

CPG of Gait located within: -is the CPG in SC able to adapt?

SC -plays important role in production of basic rhythmic mvmts that underly locomotion (produces stereotyped mvmts) Adaptive functions of SC don't come from CPG but from descending PWs from higher centers & sensory FB from periphery

What do we look for in a normal gait pattern?

SYMMETRICAL ALTERNATING PATTERN -this provides dynamic stability for normal bipedal gait with minimal control demands -described by a phase lag of .5 (meaning cycles are half way form each other- opposite) -0= not together at all -1= both legs together

Joint Kenetics?

Stance Phase -Net extensor moments (means net force needs to be in extension to hold themselves up)=> ppl use wide variety of strategies to achieve this Swing Phase -more stereotypical mvmts (we all pretty much move in the same way)

Proactive Strategies:

Uses sensory inputs to modify gait patterns -Vision is used to identify potential obstacles in the environment and to navigate around them -Prediction is used to estimate the potential destabilizing effects of simultaneously performing tasks like carrying an object while walking -Anticipatory modifications to the step cycle are made accordingly

Normal Young Adult Temporal & Distance Factors:

Walk= 1.46 m/sec (3.26 mi/hr) Mean Cadence= 1.9 steps/secs (112.5 steps/min) -110 steps/min for men -115 steps/min for women Mean Step length= 76.3 cm (30.5 in)

How does sensory feedback loss impact adaption of gait?

often leads to ataxia

As walking speed increases, proportion of time spend in swing & Stance phases changes with...

stance phase becoming progressively shorter in relation to the swing phase

As walking speeds slows..

stance time increases, while swing time remains relatively constant (time in double-support stance increases the most) -variability increases @ lower speeds (so the slower you go, the more variability you get with mvmts)

Walking is a function of:

step length & step frequency (cadence)

When people increase their walking speed, they typically lengthen:

their step & increase their pace (take larger steps & increase their cadence) Pathologies where they shorten steps when they go faster=> Parkinsons

Swing Phases:

~40% of cycle duration -intial swing -mid swing -terminal swing

Stance Phases:

~60% of the cycle duration -Initial contact -loading response -midstance -terminal stance -preswing