Performance-Based Versus Patient-Reported Physical Function: What Are the Underlying Predictors?

Abstract

Functional limitations have been operationally defined for studies of rehabilitation science through measures of physical performance and patient-reported function. Although conceived as representing similar concepts, differences between these 2 modes of measuring physical functioning have not been adequately characterized scientifically. The purpose of this study was to compare the Short Physical Performance Battery (SPPB) with the function component of the Late-Life Function and Disability Instrument (LLFDI) with respect to their association with physiologic factors and other psychosocial and health factors potentially influencing rehabilitative care. This study was a cross-sectional analysis of baseline data from a sample of community-dwelling older adults (N=137) with mobility limitations enrolled in a randomized controlled trial of exercise. A performance-based measure of function (the SPPB) and a self-report measure of function (the LLFDI) served as functional outcomes. Physiologic factors included measures of leg strength, leg velocity, and exercise tolerance test (ETT) duration, which served as a surrogate measure of aerobic capacity. Psychosocial and health factors included age, sex, height, body mass index, number of chronic conditions, depression, and falls efficacy. Separate multivariable regression models predicting SPPB and LLFDI scores described 33% and 42% of the variance in each outcome (R(2)), respectively. Leg velocity and ETT duration were positively associated with both performance-based and patient-reported functional measures. Leg strength and age were positively associated with SPPB scores, whereas number of chronic conditions, sex, and falls efficacy were associated with the LLFDI scores. This study included older adults with mobility limitations and may not generalize to other populations. Performance-based and patient-reported measures of physical function appear to assess different aspects of an older person's functioning. The SPPB was associated with age and physiologic factors, whereas patient-reported function measured by the LLFDI was associated with these factors as well as with psychosocial and health factors.