L26- Ageing of motor function and mobility

what is gait

the manner or pattern of how someone walks or moves on foot

• in biomechanics and clinical contexts, gait describes the coordinated movements of the limbs and body during walking or running

• it is proxy for mobility

what things affect gait

-Walk or Run

• Speed

• Terrain (uneven)

• Surrounding obstacles

• Weather (slippery)

• Attention

• Muscle strength & stamina

Why is gait important in ageing research?

• Proxy for overall mobility and health

• Common, everyday activity → easy to measure

• Developmentally important

  • Related to falls in older persons

  • Related to longevity

  • Activity that remains with decline

  • Cyclic patterns  balance

  • Complex integration of musculoskeletal and

  nervous systems

  • Well-developed animal and human models

what are the phases of gait

what are the temporo spatial parameters of gait

Cycle duration (stance+swing)

• Cadence (steps/minute)

• Step / stride length

• Gait speed

• Step width

• Asymmetry

• Variability

what are the other parameters of gait (not temporo spatial)

-Push-off force on the ground (asymmetry)

• Leg muscle co-contraction

• Knee angle swing (kinematics)

• Gaze direction

how can the temporo-spatial parameters of gait be measured

Markers, IMU, pressure insoles

how can the other parameters of gait (not temporo spatial) be measured

Push-off force on the ground (asymmetry)- force plates

• Leg muscle co-contraction- EMG

• Knee angle swing (kinematics)- markers, IMU

• Gaze direction- eye tracker

how many people are affected by gaot issues

35% of adults over 70 yr have clinically diagnosable gait abnormalities

what changes in gait do we commonly see with age

• Shorter steps

• Longer double support

• Shorter swing length

• Lower speed

• Less push-off power

• Hunched posture

• Reduced balance/stability

• Wider steps

• Problems navigating, turning

what causes gait speed to reduce with age

What causes this decline in speed?

- Decline in propulsive muscle strength?

Hiding by shifting ankle and hip muscles?→ sooner fatigued

what can speed and age predict

survival

• Gait speed is a simple accessible indicator of health/brain function of the older adult

what are the contributions of the CNS to gait control

what bodily functions contribute to feedback of gait control

• Visual

• Vestibular

• Auditory

• Cutaneous

• Proprioceptive

what bodily functions contribute to support of gait control

• CVS

• Pulmonary

• Bones

• Joints

• Ligaments

• Feet

Goal-directed locomotor control — brain regions & ageing effects

• Controlled by:

  • DLPFC (dorsolateral prefrontal cortex)

  • SMA (supplementary motor area)

  • Frontal cortex + associative basal ganglia loops

• Role: planning, decision-making, flexible movement

→ More sensitive to ageing → declines earlier

Habitual locomotor control — brain regions & ageing effects

• Controlled by:

  • Sensorimotor cortex

  • Sensorimotor basal ganglia loops

• Role: automatic, stimulus–response movements (habits)

→ Less sensitive to ageing → relatively preserved basic movement

what are some CNS abnormalities in older adults that contribute to mobility and cognitive decline

• White matter hyperintensities

• Brain atrophy

• Small vessel disease

• Cerebral infarcts

• Lewy Bodies

• Neuritic

• Neurofibrillary tangles

how is cognition in gait control demonstrated

• Continuous gait disturbance

• Episodic (freezing of gait)

what is cognition in gait control assed by

• Association task

• Dual-task protocols

what is the dual task principle in gait control

• Walking uses shared cognitive resources

• When doing a second task (e.g. counting + walking):

  • ↓ cognitive performance (more mistakes, slower responses)

  • ↓ gait performance (reduced walking speed)

→ Called dual-task interference
→ Shows gait requires cognitive input, not just automatic control

What does dual-task walking demonstrate about cognition and gait?

• Example tasks: naming animals, counting backwards

• Gait speed ↓ under dual-task conditions

• Strong link between gait speed and executive function + attention

• Demonstrates in real-time:

  • Attention/working memory used to compensate

  • Task prioritisation (executive function)

  • Limits of compensation

→ Sensitive to task difficulty → useful for detecting cognitive decline

what is the risk of dual task walking

falling

what 3 ways ca brain activity during walking be measured

1. Functional near-Infrared spectroscopy (fNIRS)

• measures oxygenated and deoxygenated haemoglobin

2. Electroencephalography (EEG)

• measures voltage changes

3. Functional magnetic resonance imaging (fMRI):

• imagined walking measures changes in blood oxygenation level

What does the fNIRS study show about brain activity during dual-task walking in young vs older adults?

• Dual-task (walking + talking) → ↑ PFC activity (↑ HbO₂)

• Older adults (OA):

  • ↑ HbO₂ across all walking conditions

  • BUT less efficient PFC use

  • Reduced cognitive control

• Young adults (YA):

  • Greater PFC activation specifically during dual-task

→ Ageing = less efficient neural recruitment + compensatory overactivation

what findings have been found correlating gait speed with cognitive decline

• gait speed predicts dementia

• gait speed differentiates dementia disease subtypes

• gait speed predicts MCI-mild cognitive impairment

• faster gait- associated with slower cognitive decline

how does gait and cognition interact

→ Gait and cognition are bidirectionally linked; both predict dementia and falls → assess together and target both in interventions.

what are our gaps in knowledge regarding gait and ageing

• How gait changes during the lifespan and age- related diseases – what is normal?

• Which gait deviations are biomarkers for different diseases?

• Underlying mechanism from neuropathology to gait impairment not clearly understood

• How brain reserve compensates for neuropathology

what is balance

the ability to control the position of your body above your feet

• keeping yourself upright and not fall

what is stability

the ability to resist or recover from disturbances to prevent a fall

• disturbances can be internal or external

static- standing

dynamic- moving

what are some facts regarding balance related to falls

• 1 in 3 people above 65 yrs of age fall yearly

• Increases to 50% of those above 80 years of age

• Falls are leading cause of injury in older persons

what is the fall cycle

1. increased fear of falling again

2. decreased physical activity

3. decreased physical ability

4. increased risk of falling

5. fall

• cycle repeats

what is used to make a clinical assessment of balance

the berg balance scale

14 items, 15-20 mins

• Assesses changes in static and dynamic sitting and standing balance

1. No reactive balance

2. No specific balance problems (one score)

3. Limited sensitivity: 5-point scale

What clinical tests are used to assess balance?

• short physical performance battery / SPPB → includes 30s sit-to-stand

• Berg Balance Test → gold standard, 14 static + dynamic tasks, score 0–4

• Timed Up & Go (TUG) → mobility test requiring static + dynamic balance, scored on time

• Tinetti / POMA → assesses STS + gait, rates symmetry & trunk posture

• Single Leg Stance (SLS) → ability to stand ≥5 seconds

• Functional Reach Test → distance reached (inches)

What aspects of balance do these tests measure?

• Combination of static + dynamic balance

• Functional tasks:

  • Standing

  • Walking

  • Sit-to-stand (STS)

• Assess:

  • Mobility

  • Postural control

  • Gait performance

  • Symmetry & trunk control
    → Mostly performance-based scoring

What are the limitations of clinical balance assessments?

• Subjective scoring

• Non-specific to balance systems

• Not sensitive to change

• Poor for guiding targeted interventions

• Limited distinction: standing vs movement

• Do NOT assess reactive balance (no perturbation/recovery testing)

How is balance assessed biomechanically during standing?

• Postural control assessed via:

  • Body trajectory / sway

• Challenges:

  • Many interacting variables

  • Complex relation between motion and stability
    → Focus = control of COM relative to base of support (feet)

How is balance assessed biomechanically during walking?

• Measures of dynamic stability:

  • Step variability

  • Step width (↑ width = larger support base)

  • Margin of stability (MoS)

  • (Lyapunov exponents – less commonly used)

• Limitations:

  • Ambiguous interpretation

  • Internal variability

  • Requires periodic movement

How is reactive balance assessed in perturbed walking?

• Recovery response after perturbation

• Key measures:

  • Number of steps to return to baseline

  • Margin of stability (MoS)

• Characteristics:

  • Discrete events (clear baseline vs perturbation)

  • Requires full-body motion capture

→ Captures real-world balance recovery ability

How is reactive balance (recovery response) experimentally assessed?

Perturbations applied during standing or walking:

• Standing:

  • Cable-release perturbations

  • Robot-controlled moving plate

• Walkway:

  • Obstacles from floor

  • Disappearing floor

  • Slippery surface / moving tiles

→ Used to assess balance recovery strategies after perturbation

What perturbation methods are used in treadmill-based balance assessment?

• Objects on belt

• Cable pulls (ankle or pelvis)

• Active orthosis / boot

• Split-belt treadmill

• Belt acceleration / deceleration

• Sideways treadmill translation

→ Used to create controlled mechanical perturbations during walking

What non-mechanical perturbations are used to assess reactive balance?

• Visual perturbations (VR screens, cues)

• GVS (galvanic vestibular stimulation)

• Vibrations

→ Target sensory systems involved in balance control

→ All methods assess reactive balance (ability to recover after perturbation)

how does postural control change with age

there is an increase in postural sway

how does dynamic balance change with age

• increase in step width

• increase in step variability

• body closer to / more within support area

what are our gaps in balance and ageing

• How balance changes during the lifespan and age- related diseases – what is normal?

• How to best assess balance to identify fall-prone individuals to offer fall training

• What are the underlying mechanisms of different balance problems?