Average performance and performance variability on a brief functional fine motor test reflect distinct behavioral constructs in aging.

Prior work in older adults has developed a brief functional fine motor test, which involves repeated timed trials of an upper-limb task. Performance has been associated with global and domain-specific neuropsychological tests as well as putative markers of Alzheimer's disease when scored using variability in trial time; however, the extent to which task performance depends on motor ability has not been established nor quantified. This retrospective study examined whether mean trial time and trial time variability (measured as intrasubject standard deviation in trial time) were differentially associated with standard assessments of motor and cognitive function. Forty-eight older adults with no functional impairment completed the functional fine motor test, which was compared to grooved pegboard test performance, grip strength, and Rey-Osterrieth complex figure test (RCFT) delayed recall. Generalized linear models included age, sex, education, and both scoring methods on the functional fine motor test (mean trial time and trial time variability) as predictors. Longer mean trial time was associated with slower grooved pegboard performance and lower grip strength, whereas trial time variability was not associated with either standard motor assessment. These findings, along with patterns of partial correlations, suggest that mean trial time may predominantly reflect motor function while trial time variability does not. Together, these findings highlight the value of considering both mean performance and performance variability in tasks that include multiple trials, offering an efficient approach to assessing multiple domains in older adults.