Background and purpose: Age-related loss of muscle mass and cardiovascular endurance can lead to impairments in muscle force production and cardiac function that, in turn, limit performance in activities essential to everyday living. The purposes of this study were: (1) to identify the "breakpoint" or threshold of maximal voluntary performance and performance in ordinary daily function and (2) to evaluate the predictive validity of the threshold to identify the ability to live independently without self-reported functional limitation.
Subjects and methods: Men and women (N=192; mean age=76 years, SD=7, range=65-97) were recruited from single-family community dwellings or retirement communities with multiple levels of care. Physical function was measured with the Continuous-Scale Physical Functional Performance Test (CS-PFP). Maximal voluntary performance measures included peak oxygen consumption (VO(2peak)) and isokinetic knee extensor torque (KET). Segmented linear regression models of the CS-PFP on the physical performance measures were used to determine the threshold values and their confidence intervals. A logistic regression model was used to evaluate the ability of the CS-PFP scores to identify those living independently and to further illustrate the concepts of threshold and physical reserve.
Results: Threshold values identified for VO(2peak) (20 mL x kg(-1) x min(-1)) and KET (2.5 N x m/[kg x m(-1)]) were associated with an average of CS-PFP score of 57 units. The threshold accurately predicted individuals reporting functional limitations.
Discussion and conclusion: The thresholds provide a mechanism for easily estimating an individual's physical reserve, predicting dependency in living status, and providing unbiased guidance for intervention in late-life independence.