Major findings and implications

Can we use the GaitRite walkway to accurately measure gait initiation?

(Chapter 3) Significance

The 4.6m, 80Hz GaitRite walkway was investigated as an alternative device with which to measure gait initiation (GI). The accepted gold standard of measuring GI is the force platform, which is costly and not readily transportable. The GaitRite

walkway is increasingly being used in gait research and its ease of use warranted investigation of its potential as a lower-cost alternative to the force platform.

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Findings

There was only moderate correlation between measurements of GI time on the GaitRite walkway and the force platform because measurements by the walkway systematically over-estimated GI time by fast initiators and under-estimated GI time by slow initiators. The predictive validity of the GaitRite walkwaymeasurements for falls-risk was relatively poor in comparison to that of the force platform.

Implications

This particular type of GaitRite walkway cannot be recommended for use in measuring GI, and the investigation of GI that is reported in Chapter 5 had to be confined in consequence to measurements made with the force platform for a subset (n = 128) of subjects. Advances in technology may enable later models of the GaitRite walkway to be used to measure GI, but the validity of the improved measurements will need to be verified before adoption.

Cognitive function, gait and gait variability in older people – a population-based study. (Chapter 4)

Significance

This is the first population-based study to investigate the associations between a range of cognitive tests across multiple domains and a variety of gait measures including the variability of those measures.

Findings

Consistent with previous research, the fundamental functions of executive function / attention and processing speed were found to be independently associated with each of the average gait measures. Results for gait variability showed that double support phase variability – a measure of stability and balance – was the key measure

independently associated with cognitive functions, specifically with executive function / attention, processing speed and visuospatial ability. Memory was not independently associated with any gait or gait variability measure.

Implications

Executive function / attention and processing speed, the fundamental cognitive functions that are exercised through frontal-subcortical connections, are associated not only with gait speed but with each phase of the gait cycle. These fundamental

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cognitive functions also operate to limit variability in gait, if this is the direction of causation, and particularly in double support phase. There is a hitherto unsuspected role for visuospatial ability in this regard.

Gait initiation in older people – time to first lateral movement may be the measure of choice. (Chapter 5)

Significance

There are few empirical data to guide the choice of a measure of gait initiation (GI) in older people. We investigated the statistical characteristics of the components of GI measured with a force platform, their inter-relationships and associations with sensorimotor variables, and the effect of cognitive loading on these

relationships.

Findings

There is considerable intra-individual variation in measurement of GI, and learning effects were observed under both single and dual-task conditions with marked

reductions in time taken over the first three or four trials under dual-tasking. Multiple trials are required to capture information on GI in customary circumstances and the median of trials per participant is the best summary measure. Time to first lateral movement (FLM) was most consistently associated with age, height and weight, sensorimotor variables, falls-risk score and cognitive speed, and was most responsive to dual-tasking. This component was strongly related to executive function,

processing speed and visuospatial ability, and with memory under dual-tasking. Transfer time and swing time were associated with relatively few other study factors.

Implications

Multiple trials (at least 6 per task condition per subject), summarised by the median, are recommended for GI measurement. Time to FLM may be the GI measure of choice in older people due to its relationship with the other factors and its

responsiveness to cognitive loading. Its strong associations with function in each of the four cognitive domains suggest that GI is an important target for future gait research.

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Visuospatial ability and memory are associated with falls-risk in older people – a population-based study. (Chapter 6)

Significance

This is one of the few population-based studies to examine the associations of measurements of cognitive ability in a range of cognitive domains with the PPA z- score, a physiological measure of falls risk, allowing for confounding due to age and interdependence between cognitive abilities.

Findings

In addition to the known effects of executive function / attention, visuospatial ability and memory predictors of the composite falls-risk score in this population-based study. Verbal and visual memory both contributed to the effect of memory on the falls-risk score. The associations of falls-risk with each of the cognitive functions were confounded by age, and that with processing speed was no longer statistically significant after adjustment by age.

Implications

In addition to the effects of deficiencies in the executive abilities and memory, older people seem to have a higher risk of falling if they are unable to navigate effectively between two places by judging distances and avoiding objects. Furthermore,

structural brain changes – such as age-related white matter abnormalities or neurodegeneration involving mesial temporal structures – may be relevant to the mechanisms underlying falls by older people.

Poorer cognitive function modifies the effect of poorer physiological function on multiple falls. (Chapter 7)

Significance

This is the first population-based study to examine the associations of a wide range of cognitive functions on the risk of single and multiple falls, and to investigate the combined effects of cognitive function and sensorimotor measures on the risk of falls.

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Findings

Overall, 24.4% of older adults had a single fall, and 20.2% had multiple falls. Neither cognitive function nor sensorimotor measures predicted the risk of single falls. However, the risk of multiple falls was increased by poorer visuospatial ability and some aspects of executive function. The adverse effects of greater sway, less

ambulatory activity, slower reaction time and gait speed, weaker muscle strength and poorer visual contrast on the risk of multiple falls were all greater in the presence of poorer function in any cognitive domain.

Implications

Recurring falls involve a complex interplay of cognitive deficits with deterioration in sensorimotor function. Cognitive function may be less relevant in the causation of a sporadic fall.