Movement Science week 1

## Motor Control: Definitions and Framework

What is motor control, and what does the motor system component involve?

Motor control is the ability to regulate/direct the mechanisms essential to movement (Shumway-Cook 2023). The motor system = how the CNS organises muscles/joints into coordinated movement

What do the sensory/perceptual and cognitive systems of motor control involve?

Sensory/perceptual system = how sensory info is used to select/control movement (integrating vision, tactile, vestibular input into meaningful info). Cognitive system = how attention, planning, problem solving, motivation and emotion contribute to control - movement always requires intent, so must be initiated by cognition

What 3 factors interact to shape movement, and what does the individual's motor/action system include?

Task, individual, and environment interact to produce movement behaviour. The individual's motor/action system = neuromotor component (muscle selection/activation, timing) + musculoskeletal component (strength/power, soft tissue compliance, joint stability, injury/repair)

Define the Degrees of Freedom Problem

The problem of choosing among equivalent solutions and coordinating the many muscles/joints involved in a movement

How do task type and environmental features shape movement?

Task type strongly affects neural organisation (e.g. open/unpredictable task like soccer vs closed/predictable task). Regulatory environmental features shape the movement itself (e.g. floor surface, object size/weight); non-regulatory features may affect performance without movement needing to conform (e.g. noise, crowds, low light)

## Motor Control in Early Years

What 5 features characterise development in early years?

Changes from conception to full maturity; an orderly but broad progression; a unique pattern in every child; a complex interactive process; progression from simple to complex function

List the key motor milestone ages

1 month: lifting head. 4-7 months: sitting with support / independently. 8-10 months: creeping/crawling. 9-10 months: pulling to standing. 12-13 months: independent standing. 14-18 months: walking

Why are newborns unable to achieve steady sitting, and what happens as postural stability develops?

Newborns lack organised muscle activity to control the head (strength, vision, vestibular and somatosensory input also contribute). As postural stability develops, newborn reflexes (e.g. Moro - arm abduction/extension response to a falling sensation) are inhibited and voluntary control emerges, leading to more mature, refined behaviours

Define steady state, anticipatory, and reactive balance control (with timing)

Steady state sitting balance = learning to control trunk segments. Anticipatory balance control = muscle activation before movement starts, present from ~3 months. Reactive balance control = early reactive response to a balance perturbation

What does walking require, and how does gait mature from infancy to childhood?

Walking requires practice, postural control/stability/orientation, coordination of reciprocal movements, and strength to control COG over base of support. Alternating leg movements occur ~16 weeks pre-natally. By 7 years, gait kinematics resemble adult patterns; from 7 to puberty, strength/coordination/speed continue improving efficiency

## Sensory & Cognitive Systems in Gait Development

How do vision and vestibular systems contribute to developing gait?

Vision guides locomotion via environmental layout and body orientation - without it, children walk more slowly/cautiously and can't walk straight. Otolith function development is key to walking emergence. Children under 6 use the support surface as a reference for head stability; children over 6 rely more on the vestibular system

How does cognitive load affect children's gait (dual-tasking)?

Infants fall less carrying objects because they adopt a more careful walking pattern (smaller steps, more variability) under divided attention. Children under 7 prioritise a cognitive task over gait in dual-task conditions; children (like adults) manage limited processing resources by performing tasks sequentially, not in parallel

How do toddler gait kinematics compare to a mature walker?

Toddlers show later swing onset, smaller hip flexion/extension range, and generate less ankle power compared to a mature (adult) walking pattern

## Motor Control in the Older Adult: Musculoskeletal Changes

What are the categories of contributors to healthy ageing (Park & Park 2018)?

Biological, mental, behavioural, nutritional, and socioeconomic factors

What skeletal muscle changes occur with ageing, and what are the outcomes?

Decreased number/size of motor units, contraction speed, alpha motor neurons, myosin content, nerve conduction speed and nerve terminals, plus denervation of type IIb fibres. Outcomes: decreased strength/power, sarcopenia, reduced fatigue resistance, and impaired walking/stairs/chair transfers/balance

What happens to grip strength and joint ROM with ageing?

Declining grip strength predicts future disability, morbidity and mortality. ROM loss: hip and spine ~20-30%, ankle ~30-40%, due to connective tissue changes (thicker/rougher collagen, more intertwined elastin with mineral deposits, reduced synovial fluid/viscosity, reduced cartilage water content)

## Motor Control in the Older Adult: Sensory & CNS Changes

What visual changes occur with ageing?

Decreased visual acuity (40s-60s), decreased contrast sensitivity/edge perception (40s-50s), reduced colour discrimination, slow pupillary light reflex, difficulty with depth perception/estimating vehicle speed. Common conditions: macular degeneration, cataracts, glaucoma

What somatosensory changes occur with ageing?

Decreased muscle spindle size/sensitivity, reduced GTO and cutaneous receptors, declining from 40s/50s with further significant decline (joint position sense, tactile sensation) by 60s/70s

What vestibular changes occur with ageing?

Reduced sensory cells, decreased VOR gain, hair cell degeneration after 70 years, altered gaze fixation with head movement - impacts balance, gait and QoL, more common in women

What CNS changes occur with ageing and what are the functional results?

CNS changes: decreased brain volume, loss of myelinated fibres, decreased nerve conduction velocity, altered executive functioning, motor cortex hypo-excitability. Results: decreased processing efficiency and sensory integration, altered attention capacity, decreased dual-tasking ability, more attention required for balance/mobility

## Balance in Older Adults

How does the balance response differ in older vs younger adults?

Increased reaction time, delayed muscle response (increased latency), a reversed sequence (distal before proximal muscles), and greater reliance on hip vs ankle movements

What are the causes of balance impairment in older adults?

Musculoskeletal (joint changes, weakness), sensory (vision, hearing, vestibular, somatosensory), neurological, cardiovascular, environmental (poor lighting, uneven surfaces), and iatrogenic (drugs, dehydration, over-sedation) factors

What did Patla et al (1993) find comparing 18 vs 70 year olds' stepping responses?

Older adults showed increased reaction time (31-36%), increased weight transfer time (50%), and decreased peak vertical force, all in response to a light cue to step

What balance strategies are used in response to perturbation, and how do older adults adapt?

Anterior perturbation: ankle, hip, step, or step-and-grasp strategy. Medial-lateral: one hip abducts while the other adducts, or a crossover step. Older adults may bend at the knees to lower COG, use arms sooner, step early, or take multiple steps to regain balance

What is the significance of single leg stance time with age?

Single leg stance time declines fairly linearly with age; a stance time under 10 seconds is associated with an increased hazard ratio for hip fracture

## Gait Changes with Ageing

What kinematic and spatiotemporal gait changes occur with ageing?

Kinematic: reduced step length, more flexed posture, reduced swing, more anterior pelvic tilt, increased lumbar lordosis. Spatiotemporal: decreased speed/step length, increased cadence relative to speed, increased step width/stance time/double support, and increased variability

How does gait speed change with age, and what speeds matter functionally?

Gait speed is fairly well maintained until ~70, then declines ~10-15%, while energy cost of walking increases past 70. Speeds under 1.0 m/s significantly impact community mobility; crossing roads safely requires over 1.2 m/s (Grim Reaper's preferred speed = 0.82 m/s, max = 1.36 m/s)

What is the relationship between walking speed and mortality, and what are the causes of reduced gait speed?

Walking faster than the median for one's age is associated with longer life expectancy (and vice versa). Causes of reduced gait speed span MSK, neurological, sensory, cardiovascular, environmental, psychological and iatrogenic factors

How do hip/ankle joint contributions to gait change with ageing?

Wider base of support, increased external rotation of the lower limb, decreased hip/knee/ankle flexion in swing, decreased hip extension/ankle plantarflexion in stance. Hip joint moments contribute more to the support moment (74% vs 37% in young), while ankle moments contribute less (12% vs 28%)

## Introduction to Observational Movement Analysis (OMA)

What is the purpose of OMA, and what is a 'hypothesised contributing factor'?

OMA's purpose is to understand how a person moves and the strategies they use, using a structured approach to increase validity/reliability. A 'hypothesised contributing factor' is a hypothesis about the impairments contributing to a movement disorder, to be confirmed later via impairment assessment

Describe the OMA clinical reasoning process

Observe functional task performance -> is movement normal? -> is there a disorder? -> hypothesise why -> test hypotheses with impairment assessments

Compare instrumented vs smartphone-based gait measurement systems

Instrumented systems (video capture, force plates, EMG - e.g. Vicom, GAITRite) are the 'gold standard' but very expensive (6 figures) and mostly in specialist centres. Smartphone apps are increasingly available, generally less accurate but with acceptable validity - a rapidly developing field

What should be standardised when preparing for OMA, and how many repetitions should be observed?

Standardise the environment/starting position (e.g. flat 10m walking surface; chair height/hand use for sit-to-stand) and your instructions, while minimising interference and maintaining safety. Observe at least two repetitions - use the first to check understanding/safety/goal achievement, and the second to narrow focus onto essential movement components

How can motor skills be divided into phases for observation?

Skills can be divided into phases (e.g. gait: stance phase - initial contact, loading response, mid-stance, terminal stance, pre-swing; and swing phase - initial swing, mid-swing, terminal swing; sit-to-stand: 2 or 4 phases). Skills without named phases can be thought of as initiation, execution, termination

In what orders can you observe a movement during OMA?

By sides, by phase, by joint, or from distal to proximal (or vice versa), depending on the movement being assessed

## Characteristics of Movement (OMA)

Define the 3 'A' characteristics of movement observation

Amplitude = range of motion used to achieve the movement. Alignment = relationship between body segments or to the base of support. Accuracy = amount of measurable error in the movement (e.g. cm of error reaching to a target)

Define the 5 'S' characteristics of movement observation

Sequencing = order of movements used to achieve the task. Symmetry = similarity of movement right vs left. Stability = ability to maintain COM relative to base of support. Speed = velocity of a body segment or time to complete the movement. Smoothness = movement without disruptions to velocity or direction

## Movement Compensation and Problem Solving

Define movement compensation, and how does it differ kinematically from a primary problem?

A movement compensation is a new movement adopted (often after injury/illness) to still achieve the task goal - e.g. restricted knee flexion leading to greater trunk flexion in sit-to-stand. A primary problem typically looks like a decrease in expected movement; a compensation looks like an increase (an added movement)

Why is it important to distinguish a primary movement problem from a compensation?

Treating the compensation instead of the primary problem is unlikely to improve the person's ability to complete the movement

What can you do if a patient can't perform a movement, or performs it too easily?

If they can't do it: modify the task (e.g. more thigh support) and/or environment (e.g. higher chair), or add verbal cues/prompts. If they do it easily with no deviations after 2+ reps: increase task/environment complexity (e.g. faster gait speed, head turns, or a secondary task) to reveal deviations

How do observations inform hypotheses about contributing impairments?

Reduced amplitude -> hypothesise restricted joint ROM/muscle length, loss of strength, or pain. Movement that's not smooth or inaccurate -> hypothesise altered proprioception or impaired motor control/strength. Altered movement sequencing -> hypothesise a motor control problem

## Biomechanics of Sit to Stand: Phase Models

Why is sit-to-stand demanding, and what did Hughes, Myers & Schenkman (1996) find about chair height and strength?

Standing up translates body weight from a large base of support (buttocks/back/feet) to a small one, requiring lower limb strength, coordination and ROM. Elderly participants used 97% of available knee extensor strength to rise from the lowest chair they could manage (40cm), vs only 39% for younger people from a 30cm seat

Describe the two-phase model of sit to stand

Phase 1 = pre-extension phase (ends when buttocks leave the seat). Phase 2 = extension phase (ends when the body is upright and stable)

Describe Phases 1 and 2 of Schenkman's four-phase model of sit to stand

Phase 1 = flexion momentum phase (starts at initiation of standing, ends just before buttocks leave the seat; body remains stable, supported by chair). Phase 2 = momentum transfer phase (buttocks leave seat to max ankle dorsiflexion; high stability demand as COM moves to limits of stability)

Describe Phases 3 and 4 of Schenkman's four-phase model of sit to stand

Phase 3 = extension phase (to max hip extension; moves head/arms/trunk to vertical; reduced stability demand vs Phase 2). Phase 4 = stabilization phase (starts after max hip extension, ends when all balance-related movement has ceased)

## Biomechanics of Sit to Stand: Kinematics, Kinetics & EMG

What are the essential kinematic components of standing up?

Feet back behind knees (ankle dorsiflexion ~30 degrees); trunk forward flexion with anterior pelvic tilt (max velocity reached here); anterior tibial translation; hip and knee extension with feet moving to plantar flexion; maintaining hip/knee extension

What are the essential kinematic components of sitting down?

Hip and knee flexion with trunk inclination from the hips; ankle dorsiflexion with forward tibial translation

Describe the kinetic demands of sit to stand and COM velocity timing

Sit-to-stand requires horizontal and vertical force generation, with eccentric braking forces at the trunk/hip controlling horizontal trajectory. Horizontal COM velocity peaks just before thighs-off; vertical velocity peaks at thighs-off, followed by controlled deceleration

Which muscles initiate sit to stand, and what are their roles?

Tibialis anterior initiates movement (anticipatory postural activity, stabilises the foot, translates tibia forward). Iliopsoas initiates trunk flexion at the start

What are the roles of rectus femoris and biceps femoris in sit to stand?

Rectus femoris contributes to hip flexion and knee stabilisation. Biceps femoris slows hip flexion before movement reverses to extension, then (with foot fixed) helps pull the shank back to assist knee extension alongside vastus lateralis

How do seat height and using the arms affect sit to stand biomechanics?

Increasing seat height decreases hip/knee forces required; using the arms decreases knee/hip extensor forces required

How does foot position affect sit to stand efficiency?

Feet placed further behind the knee are more efficient than plantar-grade ankles; asymmetrical foot placement increases load on the more posterior foot

How do balance, ROM, body weight, pain and vision affect sit to stand?

Balance disorders increase movement time; knee flexion under 100 degrees requires higher hip angular velocity; heavier body weight requires more vertical force and reduces hip flexion (needing more knee extensor force); pain increases apprehension; intact depth perception/contrast sensitivity increases safety