Physical functioning is related to both an impaired physical ability and ADL disability: A ten year follow-up study in middle-aged and older persons

Abstract

Objective

Identification of measures of physical function that mediate or link impaired physical ability with disability in activities of daily living (ADL) is necessary to facilitate the development of interventions to prevent or delay the onset of ADL disability. We examined whether measures of physical function at baseline are determinants of the Short Physical Performance Battery, as measure of physical ability, and disability, at ten years follow-up.

Study design

Prospective cohort study in 625 middle-aged and older persons.

Main outcome measures

Physical ability was measured by Guralniks Short Physical Performance Battery (impaired physical ability: score <6) and ADL ability by the KATZ questionnaire (ADL disability: score ≥1). Physical function was measured by lung function (in men only), handgrip strength, leg strength, and physical activity. The associations between physical function and the dichotomized impaired physical ability and disability-score were estimated using Poisson regression.

Results

Better lung function and higher leg strength were associated with a lower risk of having impaired physical ability, RR = 0.98, 95% CI [0.96; 0.99] per 10 L/min and RR = 0.97, 95% CI [0.94; 0.99] per 10 Nm, respectively.

Higher handgrip strength, leg strength and level of physical activity were associated with a lower risk of having ADL disability, RR = 0.72, 95% CI [0.57; 0.92] per 10 kg, RR = 0.95, 95% CI [0.92; 0.98] per 10 Nm, RR = 0.98, 95% CI [0.96; 0.99] per point-score, respectively.

Additional adjustment for baseline ADL disability did not materially changed the point-estimates (except for handgrip strength).

Conclusion

Overall, leg extensor strength was associated with both an impaired physical ability and ADL disability. Other measures of physical functioning were either related to an impaired physical ability or ADL disability. ADL disability may be an intermediate factor for hand grip strength in the causal chain from impaired physical ability to ADL disability at follow-up. The results of this study show that leg strength might be a relevant parameter to consider for future intervention studies.

Introduction

Older persons (>65 years) are at risk of functional decline, which is one of the greatest threats for independency, as it can progress into functional limitations and eventually lead to disability [1]. Nowadays, as the general population is aging and the number of older persons is increasing, more people are at risk of disability in activities of daily living (ADL).

The prevalence of functional limitations and ADL disability in older persons is estimated at 20–30%, this percentage increases with age [2]. Disability is a dynamic process in which older persons both develop disability and recover from a period of disability [3], [4]. In a previous study, a recovery rate of 81% was reported within 12 months after the first episode of disability [5]. Still, the functional status at one moment in time is a strong predictor of the survival and future functional status in older persons [6].

ADL disability is often studied as the outcome. However, for preventive purposes it is also important to identify persons who are in a preclinical stage of disability. A previous study showed that the rate of progressing from intermittent disability to continuous disability is high and the likelihood of regaining sustained independence after an episode of continuous disability is low [4]. This stresses the importance of intervening in an early stage of the disabling process.

Physical impairment is an important component of disability, tends to occur early in the disabling process [7], and is characterized by irreversible changes in the sensory-motor performance of a person [8]. Hence, physical impairment may be a suitable target for preventive strategies. A potential measure of physical impairment is the Short Physical Performance Battery, as it objectively assesses the capacity of a person to perform activities of daily life and is useful in predicting disability [9]. However, the relations between measures of physical functioning and the Short Physical Performance Battery are still unknown.

The identification of measures of physical function that mediate or link impaired physical ability with ADL disability is necessary to facilitate the development of interventions to prevent or delay the onset of ADL disability. The aim of the present study is to examine whether measures of physical function (i.e., lung function, isometric handgrip strength, leg extensor strength and physical activity) at baseline are related to the Short Physical Performance Battery, as a measure of impaired physical ability, and level of disability, at ten years follow-up in middle-aged and older persons. In addition, we examine whether baseline ADL disability is an intermediate factor in the causal chain from an impaired physical ability to ADL disability at follow-up.