This study investigated the consistency of IC models based on different locomotion assessments with the WHO IC model. Our results indicated that IC models based on FTSST, GS, and TUG assessments of locomotion were in good agreement with the WHO IC model, while the consistency of the HG model was poor. As HG only reflects muscular strength in the upper extremity, it cannot provide insights into the functioning of other organs and systems, such as the skeletal, nervous, and vestibular systems. Our findings support the notion that HG alone should not be used to evaluate the locomotion dimension of IC. In contrast, the FTSST, GS, TUG, and SPPB are comprehensive assessments that include measures of lower limb muscle strength, joint function, and balance ability. Further, these assessments have demonstrated good test-retest and inter-rater reliability [13]. When compared with the WHO IC model, the FTSST IC model was most consistent. In the old-old, the FTSST may be more appropriate than other indicators of physical performance given that it is simple to perform, does not require much space, and is easy to assess. There are also some drawbacks to the FTSST, which may not be suitable for older people with knee disease. The WHO recommends the SPPB given that the test is comprehensive and can avoid floor effects in different populations. However, due to the relatively long evaluation time and the need to calculate scores, it may not be suitable for widespread promotion in community-dwelling older people.
In terms of predicting adverse health outcomes, IC decline based on FTSST, GS, and TUG models had similar predictive power for falls and functional decline when compared with the WHO IC model, validating the feasibility of these three models. IC decline based on the HG model was not significantly associated with falls or functional decline after adjusting for age, sex, and CCI. HG has been identified [24] as a strong predictor of all-cause mortality and cardiovascular events. The end points selected in the present study mainly reflected a decrease in comprehensive coordination and were designed to screen for those at high risk of disability. Our results suggest that HG is not suitable for early prediction of functional decline in the old-old.
In China, the management of community-dwelling older people has always been centred on disease. Zhao et al. [25] found that IC decline was associated with higher odds of 1-year functional decline than multimorbidity in community-dwelling adults ≥ 65 years old. Our findings also indicated that IC decline can predict falls and functional decline in the old-old after adjusting for comorbidity, which is in line with the concept of healthy aging proposed by WHO and provides a reference for developing value-centred medicine. The selection of appropriate methods for assessing IC, multi-domain interventions, and integrated care [26] may reduce the incidence of adverse health outcomes in older patients.
In this study, the proportion of IC decline was 76.9%, mainly reflected as impairment in the locomotion dimension. Zhao et al. [25] reported that the proportion of IC decline increased with age among community-dwelling older people in China, increasing from 58.7% in those aged 65–74 years to 72.0% and 80.6% in those aged 75–84 years and ≥ 85 years, respectively, which was consistent with our findings. However, the main dimensions contributing to IC decline have varied among studies, which may be explained by the different methods used to assess each dimension and differences in external environmental support or demographic characteristics. Locquent et al. [27] assessed only four dimensions of IC, excluding the sensory dimension, reporting that most impairments occurred in the psychology dimension (GDS, 32.0%), followed by the locomotion dimension (SPPB, 27.2%). Zeng et al. [8] adopted the same method used in the current study and reported that most impairments occurred in the sensory dimension (self-reported, 62.0%), followed by the locomotion dimension (GS, 58.4%). However, in their study, the sensory dimension was assessed as only good or poor, which may have increased the proportion of residents reporting impairments in this dimension. As we only examined the consistency of IC models based on different measures in the locomotion dimension, it may be necessary to test the consistency of methods for evaluating other dimensions, especially vitality. This may help to provide a standardized reference for different studies in various countries and may provide insight into the epidemiological characteristics of IC decline.
Strengths And Limitations
This study is one of the few studies to evaluate the consistency of IC models based on different locomotion assessments and the relationship of each model with adverse health outcomes using a cohort design. First, our data provide more options for the clinical application of methods for assessing IC, as well as a reference for the standardization of methods across different studies. Second, the study was conducted among a population of the old-old, filling a gap left by previous research related to IC. Third, as functional ability is determined based on both IC and the environment, our study is advantageous in that all participants resided in a Continuing Care Retirement Community with a relatively consistent external environment, helping to avoid the interference of some confounding factors.
However, our study had some limitations. First, the cut-off value for decline in locomotion dimension may not apply to the old-old, and there is a lack of evidence regarding reference values for this population in China. Second, data from more communities should be collected for verification in the future. Third, the adverse health outcomes in this study only included falls and functional decline, and more adverse health outcomes, such as all-cause mortality, should be included in future studies.