Is there a threshold between peak oxygen uptake and self-reported physical functioning in older adults?

Purpose: Few studies have examined the relationship between directly measured oxygen uptake ((V) over dot O-2) and self-reported physical function (PF). The purpose of this study was: 1) to examine the relationship between peak (V) over dot O-2 and PF and 2) to determine whether a threshold or cut point exists that distinguishes between individuals reporting required assistance in the performance of functional tasks (low PF) and those who report ability to perform tasks independently (high PF). Methods: Participants were 161 community-dwelling adults, ages 65-90, who had a baseline evaluation for a clinical trial that included measurement of peak (V) over dot O-2 and PF. PF consisted of a summary score combining scores from the Older Americans Resources and Services Multidimensional Functional Assessment Questionnaire, Nagi Disability Study, Rosow-Breslau Scale, Physical Function Scale of the Medical Outcomes Study, and the Falls Efficacy Scale. Decision tree, cubic spline, and logistic regression analyses explored these relationships with age, gender, education, race, body mass index, depression, and total number of chronic diseases included as important covariates. Results: Among all covariates examined, peak (V) over dot O-2 was most strongly associated with (P = 0.004) with PF. There was no threshold effect. Decision tree analyses indicated that 18.3 mL . kg(-1) . min(-1) was the optimal cut point distinguishing between low PF and high PF (P < 0.0001). Between-gender differences in PF(P = 0.002) were no longer significant when peak (V) over dot O-2 was included in the PF model (P = 0.17). Conclusions: These data indicate that individuals with a peak (V) over dot O-2 < 18 mL . k(-1) . min(-1) report significant difficulty in the performance of daily tasks and that differences in peak (V) over dot O-2 may explain, in part, why women report more impairment in PF.