motor control

What is motor control?

The ability to regulate or direct the mechanisms essential to movement.

What 3 systems contribute to motor control?

1. Motor/action system 2. Sensory/perceptual system 3. Cognitive system

What does the motor/action system involve?

Neuromotor factors (muscle selection, activation, timing and coordination) and musculoskeletal factors (strength, power, soft-tissue compliance, joint stability and injury/repair).

What is the degrees-of-freedom problem?

The CNS must choose among many equivalent movement solutions and coordinate many muscles and joints to produce a functional movement.

What does the sensory/perceptual system do?

Integrates sensory input into meaningful information about the state of the body and features of the environment important for movement regulation.

What does the cognitive system contribute to motor control?

Attention/awareness, planning, problem solving, motivation, emotion, CNS processing/reaction time, memory/learning, dual-tasking and behaviour.

What factors interact to influence movement behaviour?

The individual, task and environment.

How does task type affect motor control?

Different functional tasks require different movement strategies and strongly influence the neural organisation of movement.

What are regulatory environmental features?

Features that shape or constrain movement, such as floor surface and the size, shape or weight of an object.

What are non-regulatory environmental features?

Features that may affect performance but do not require the movement itself to conform, e.g. background noise, crowds, distractions or low light.

What is motor development?

Changes occurring from conception to full maturity, progressing in an orderly but broad sequence; each child has a unique pattern and development progresses from simple to complex function.

What are motor milestones?

Predictable sequences of motor behaviours that emerge during development.

Why can't newborns achieve steady-state sitting?

They lack sufficiently organised muscle activity to control the head/trunk; strength and visual, vestibular and somatosensory contributions also influence head control.

What are the 3 stages of postural control described for sitting?

1. Steady-state sitting balance 2. Anticipatory balance control 3. Reactive balance control.

When is anticipatory balance control present?

From around 3 months of age.

What is reactive balance control?

The ability to respond to perturbations of balance; early responses are often stereotypical.

By what age are children's kinematic, joint torque and propulsion patterns similar to adults?

Around 7 years.

What changes from about 7 years to puberty?

Strength, coordination and speed of motor skills increase, improving gait efficiency.

How does vision contribute to locomotion?

It guides locomotion by providing information about environmental layout and the body's orientation relative to the environment.

How does reduced vision affect gait?

Walking becomes more cautious.

Why is head, arm and trunk (HAT) control important in infant mobility?

Control of HAT segments is a critical component of controlling mobility.

How do infants use the environment when learning to walk?

They use surfaces that provide stability, such as walls and rails, to support safe locomotion.

How does a secondary attention-demanding task affect infant walkers?

They become more cautious and have limited attentional resources available to maintain gait while performing a manual task.

How do children under 7 years manage dual tasks compared with adults?

They tend to prioritise the cognitive task over gait and manage limited processing resources sequentially rather than in parallel.

What factors contribute to healthy ageing?

Biological, mental, behavioural, nutritional, socioeconomic, genetic, gender, environmental and cultural factors.

What happens to skeletal muscle motor units with ageing?

Number and size of motor units decrease; alpha motor neurons/cells and nerve terminals also decrease.

What happens to muscle contraction speed with ageing?

It decreases.

What happens to myosin protein content with ageing?

It decreases.

What happens to motor nerve conduction speed with ageing?

It decreases.

What happens to type IIb fibres with ageing?

They undergo denervation; these fibres are strong and fast-twitch.

What are the functional outcomes of age-related muscle changes?

Reduced strength, power, muscle mass (sarcopenia) and fatigue resistance, affecting walking, stairs, transfers and balance.

How much ROM is typically lost with ageing at the hip, spine and ankle?

Hip: ~20–30%; spine: ~20–30%; ankle: ~30–40%.

Why does ROM decrease with ageing?

Collagen changes, mineral deposits in elastin, reduced synovial fluid, reduced cartilage water content and reduced activity levels.

What visual changes occur with ageing?

Reduced visual acuity, contrast sensitivity and edge perception; poorer colour discrimination; slower pupillary light reflex; reduced depth perception and difficulty estimating approaching vehicle speed.

How can shadows or colour changes affect older adults?

They may be interpreted as changes in floor level, increasing difficulty with navigation and balance.

What happens to muscle spindles with ageing?

Muscle spindle size and sensitivity decrease.

What happens to Golgi tendon organs (GTOs) with ageing?

GTO receptor number decreases.

What happens to cutaneous receptors with ageing?

Number and size decrease, including receptors such as Meissner's corpuscles.

How does joint position sense change with ageing?

It decreases, particularly in the lower limbs; impairment is typically greater at the foot than knee, then hip.

How does tactile sensation change with ageing?

Tactile acuity and two-point discrimination decrease.

What happens to the vestibular system with ageing?

Sensory cell numbers decrease and vestibular problems become more common, particularly after 60.

What happens to VOR gain with ageing?

VOR gain decreases, contributing to difficulty maintaining visual fixation during faster head movements.

What factors can worsen balance problems related to vestibular/visual ageing?

Poor or changing lighting, darkness, unstable surfaces and walking with head movement.

What CNS changes occur with ageing?

Reduced brain volume, loss of myelinated nerve fibres, reduced nerve conduction velocity, executive-function changes and motor cortex hypoexcitability.

What are the effects of age-related CNS changes on motor control?

Reduced central processing efficiency and sensory integration, reduced attention and dual-task capacity, and greater attentional demands for balance and mobility.

What is an example of reduced dual-task capacity in older adults?

An older person may stop walking while talking.

How does reaction time change with ageing?

It increases.

How does muscle response latency change with ageing?

Muscles take longer to respond.

How do balance strategies change with ageing?

The usual proximal-to-distal sequence may be disrupted; older adults tend to use hip strategies more than ankle strategies.

Why may older adults rely more on hip strategies?

Weakness, sensory changes and loss of ROM can reduce the effectiveness of ankle-based strategies.

What are musculoskeletal causes of balance impairment?

Degenerative joint changes and muscle weakness.

What are sensory causes of balance impairment?

Poor vision/hearing, vestibular problems and somatosensory decline.

What are neurological causes of balance impairment?

Seizures, drop attacks, TIAs, Parkinson's disease and reduced dual-task ability.

What are cardiovascular causes of balance impairment?

Postural hypotension and dysrhythmias.

What environmental factors can impair balance?

Poor lighting and uneven surfaces.

What iatrogenic factors can impair balance?

Medications/drugs, cardiac dysrhythmias, dehydration and over-sedation.

What happens to COM movement in older adults during a balance perturbation?

COM movement increases before stabilisation.

What happens to ankle movement during balance perturbation in older adults?

Ankle movement decreases.

What alternative strategies can older adults use when a perturbation is too large?

Bending the knees, using the arms or taking a step.

How does gait generally change with healthy ageing?

Walking becomes slower with shorter steps, reduced arm swing, wider base of support and more time spent in stance/double support.

What spatiotemporal gait changes occur with ageing?

Decreased speed and step length; increased cadence at the same speed, step width, stance time, double support and variability.

Why is increased gait variability concerning?

Greater within-person variability may be associated with morbidity.

What gait speed is generally needed for community mobility?

Gait speed below 1.0 m/s has a significant impact on community mobility.

What gait speed is needed to cross a road?

More than approximately 1.2 m/s.

What is the relationship between gait speed and mortality/morbidity?

Higher gait speed is associated with a higher likelihood of living longer and generally better health outcomes.

What musculoskeletal factors reduce gait speed?

Reduced muscle strength, arthritic pain, osteoporosis, podiatric pain and fractures.

What neurological factors reduce gait speed?

Stroke, Parkinson's disease and cognitive factors; reduced social interaction can also contribute.

What sensory factors reduce gait speed?

Vision impairment, reduced proprioception, peripheral neuropathies and vestibular dysfunction/dizziness.

What cardiovascular factors reduce gait speed?

Angina, congestive heart failure, peripheral vascular disease and pulmonary disease.

What environmental factors reduce gait speed?

Stairs, uneven surfaces, loose carpets, architecture and poor lighting.

What psychological factors reduce gait speed?

Fear of falling, attitudes/beliefs, depression and anxiety.

What iatrogenic factors reduce gait speed?

Sedation, prolonged inactivity/bed rest and medications.

What kinematic gait changes occur with ageing?

Wider BOS, increased lower-limb external rotation, reduced hip/knee/ankle flexion during swing, and reduced hip extension and ankle plantarflexion during stance.

What is the lower-limb support moment?

The combined extensor moments of the lower limb that help prevent collapse of the limb.

How does the hip contribution to the support moment change with age?

It increases: approximately 74% in older adults compared with 37% in young adults.

How does the ankle contribution to the support moment change with age?

It decreases: approximately 12% in older adults compared with 28% in young adults.

What is the key role of postural stability in young children?

It provides the foundation for development of movement and functional motor skills.

What systems contribute to development of postural control?

Multiple sensory and motor systems interact to develop postural control.

How does postural stability change in older adults?

Reaction time increases, responses to perturbations are smaller/altered, and different stabilisation strategies are used.

What are the major gait changes in older adults?

Reduced gait speed and step length, with broader changes in spatiotemporal, kinematic and kinetic patterns.

What domains can explain age-related changes in postural stability and gait?

Motor, sensory and cognitive domains.