Sex Differences in Concomitant Trajectories of Self-Reported Disability and Measured Physical Capacity in Older Adults

Abstract

Background: Despite documented age-related declines in self-reported functional status and measured physical capacity, it is unclear whether these functional indicators follow similar trajectories over time or whether the patterns of change differ by sex.

Methods: We used longitudinal data from 687 initially nondisabled adults, aged 70 or older, from the Precipitating Events Project, who were evaluated every 18 months for nearly 14 years. Self-reported disability was assessed with a 12-item disability scale. Physical capacity was measured using grip strength and a modified version of Short Physical Performance Battery. Hierarchical linear models estimated the intra-individual trajectory of each functional indicator and differences in trajectories' intercept and slope by sex.

Results: Self-reported disability, grip strength, and Short Physical Performance Battery score declined over 13.5 years following nonlinear trajectories. Women experienced faster accumulation of self-reported disability, but slower declines in measured physical capacity, compared with men. Trajectory intercepts revealed that women had significantly weaker grip strength and reported higher levels of disability compared with men, with no differences in starting Short Physical Performance Battery scores. These findings were robust to adjustments for differences in sociodemographic characteristics, length-of-survival, health risk factors, and chronic-disease status.

Conclusions: Despite the female disadvantage in self-reported disability, older women preserve measured physical capacity better than men over time. Self-reported and measured indicators should be viewed as complementary rather than interchangeable assessments of functional status for both clinical and research purposes, especially for sex-specific comparisons.

Keywords: Disability; Physical capacity; Sex differences; Trajectories.

Figure 1.

Trajectories of disability* and physical capacity^† by sex and length-of-survival (1998–2012). Dotted lines show estimated trajectories for participants who died after 6 years of follow-up. Continuous lines show estimated trajectories for participants who were alive at last assessment. *Disability assessed as “self-reported need for help.” ^†Upper-extremity capacity assessed using grip strength and lower-extremity capacity assessed using Short Physical Performance Battery (SPPB) score.