| Multiple cross-sectional studies have shown a positive association between cognitive decline and physical functional decline in demented older adults, and new research has begun to look at the temporal ordering of decline in physical and cognitive functioning prior to and following physical disability and diagnoses of mild cognitive impairment (MCI) or dementia. With the physical and mental health fields moving toward a preventative treatment approach, it will be necessary to identify modifiable factors that influence progression to physical disability and dementia in older populations. Due to difficulties recruiting older adults for clinical research trials, the inequitable geographic distribution of clinical research trials for older adults, and limitations imposed by financial problems on many of the nation's elderly, it will be important to identify clinical interventions that can be implemented by clinicians across a broad array of clinical settings. In addition, because of increasing job commands faced by many of today's clinicians, future research must provide improved metrics for the clinical assessment of cognitive and physical functioning in everyday clinical settings in ways that are not only efficacious, but also efficient and cost-effective. However, our current understanding of the association between physical functioning and cognitive status is insufficient. A gap in the existing literature exists with regard to the interplay between cognitive functioning and physical proficiency in the absence of pathology. Little research has examined the association between cognitive and physical functioning in cognitively and physically healthy older adults. What is also unclear is how the variance in demographic variables (age, gender, years of education) affects the association between cognition and physical proficiency. The present study used retrospective data from the National Alzheimer's Coordinating Center (NACC), a national database of data from participants participating in ongoing standardized clinical research at the nearly 30 Alzheimer Disease Centers (ADCs) nationwide. Data from 119 cognitively healthy, community-dwelling older adults were analyzed using confirmatory factor analyses (CFA) within a structural equation modeling (SEM) format. First, one-factor models evaluated cognitive functioning and physical functional speed as two individual latent constructs. Cognitive functioning was defined with four reflective indicators: Category Fluency -- Animals, Stroop Color Naming, Digit Symbol, and Block Design. Physical functional speed was defined as a latent factor with five reflective indicators: Step Test, Time Up and Go, Walk 50 Feet, and 5-Second Chair Rise. Both one-factor models had adequate model fit, with all indicators significantly loading on their respective factors. A two-factor model then examined the relationship between the two latent constructs, and fit indices showed adequate model fit. The final model included multiple indicators multiple causes (MIMIC) to examine the moderating effects of three indicators (age, gender, and years of education) on the strength of the relationship between cognitive functioning and physical functional speed and overall model fit. After adjusting for covariates, model estimates were smaller but still demonstrated acceptable model fit. Finally, Differential Item Functioning (DIF) was employed to examine direct effects of covariates on specific indicators selected based on modification indices. Findings from the present study demonstrate an association between cognition and physical functioning without evidence of pathology, and highlight the ways in which the interplay between both factors are affected by demographic characteristics. The study also illustrates a parsimonious way of assessing for cognitive status and physical ability in older adult populations. These findings are significant as they contribute to the improved understanding of the interplay between physical and cognitive health among older adult populations. This information serves to better inform research directed toward better defining characteristics of the normal aging process, improving interventions for cognitive and physical functional decline, and continuing existing efforts to maximize the overall functioning of older adults. |
