The present study is the first to report sex-specific reference values for SPPB among community-dwelling adults aged 21–80+ years old in Singapore. Furthermore, SPPB cut-off score of ≤11 was optimal for discriminating sarcopenia in this Asian cohort of community-dwelling older adults, based on AWGS19 definitions. The study results also suggest that regardless of sex, the GS subtest could be useful in assessing sarcopenia in our population.
In our study population, more than half of participants aged 21–80 years and over a third participants aged >80 years achieved the maximum SPPB score of 12. This implies a ceiling effect for SPPB in our population, as >20% of men and women across all age groups achieved the highest possible score (23). Our findings agree with a Norwegian study which reported ceiling effects of SPPB, across age groups 40–80+ years (3). However, such a ceiling effect of SPPB was not observed in Colombian adults aged >80 years, with 19.8% of males and 7% of females with an SPPB score of 10–12 (4). Across ages 40–80+ years, mean SPPB scores in men and women were similar between our study participants and Norwegian adults (3). Compared with Colombian older adults (60–80+ years), the mean SPPB in our population was higher in both sexes (by ~2–3 points) (4). These findings suggest that SPPB scores differ by population and population-specific reference values are necessary. The presence of ceiling effects in our population support the need to report specific SPPB subtest values, rather than aggregated scores, in order to better classify physical performance in community-dwelling older adults with higher functional ability. The disparity in SPPB scores between populations could be due to socio-economic, racial or ethnicity differences. For example, poverty and lower education were associated with greater likelihood of physical functioning limitation among older adults aged >60 years (15). In older adults aged ≥65 years, non-Hispanic blacks had poorer SPPB scores and greater mobility disability than non-Hispanic whites, implying that race and genetic factors could also affect physical function (14). Therefore, it is important to report population-specific SPPB and individual subtest values in community-dwelling adults.
Sarcopenia is associated with functional decline, increased risk of frailty, falls and mortality (24), which contribute to huge personal, social and economic burdens (25). In our study, the prevalence of sarcopenia and severe sarcopenia combined was 30–41% in men and 23–40% in women, justifying the need for markers such as SPPB, to assess sarcopenia and poor physical function in a quicker and easier manner among the wider population. The present study showed that SPPB cut-point of 11 gave the optimal sensitivity (42–58%, 67–100%) and specificity (69–70%, 68–75%) for assessing sarcopenia and severe sarcopenia respectively, in community-dwelling adults ≥60 years. This cut-off was higher than the recommended SPPB cut-point of ≤8–9 suggested by EWGSOP and AWGS19 SPPB criteria for sarcopenia (10, 11, 26, 27). Other studies also reported SPPB cut-points of 7–9 being associated with higher mortality risk (28-30). Differences in study populations likely explain the disparity. Our study participants were community-dwelling older Asian adults with high functional ability, which differed from other studies involving Caucasians (29), outpatient or hospitalised individuals who might have limited physical function (28, 30). Furthermore, SPPB scores are commonly stratified into groups (0–3, 4–6, 7–9, 10–12), with a score of 10–12 as the reference (normal) group (7, 26, 31). Within individuals with SPPB score 10–12, varying physical function, risk of sarcopenia and mortality plausibly exist. Compared with individuals with maximum SPPB score, individuals with score of 11 were 1.4 times more likely to develop mobility disability in a 3-year follow-up study (32). These results suggest that a 1-point decrease in SPPB score could impact physical function (33). Therefore, in functional community-dwelling older adults, a higher SPPB cut-off can better discriminate sarcopenia.
We compared the performance of individual SPPB subtests in assessing sarcopenia. Our results demonstrate that GS, but not STS subtest, generally had better performance than total SPPB score in discriminating sarcopenia. Among our participants, GS cut-off of 1.0 m/s gave optimal sensitivity (57–70%) and specificity (68–72%) in assessing sarcopenia in men and women, and severe sarcopenia in women. GS cut-off of 0.9 m/s was optimal for severe sarcopenia in men. Our findings agree with the recommended AWGS19 cut-off for GS criteria, despite a different walk distance of 6m in AWGS19 and 8ft in the present study (11). Other studies also reported a GS of <1.0 m/s in sarcopenic older adults (34), and found greater dementia risk and poorer health outcomes in adults >80 years with GS of <1.0 m/s (35, 36). However, GS cut-off recommendations varied according to sarcopenia-associated health outcomes, such as hospitalisation, falls, mortality, cognitive impairment (37). For example, other studies including the EWGSOP recommended a GS cut-off of 0.8 m/s (10, 12, 38), due to its association with lower life expectancy (39) and disability (37). Nonetheless, GS cut-offs are dependent on health status and demographics, supporting the need for population-specific studies investigating the diagnostic value of GS in sarcopenia. Herein, we propose that the GS subtest of SPPB might be a useful, simple and accessible tool for assessing sarcopenia in functional community-dwelling older adults.
Our study used a well-established performance-based physical function assessment and recruited randomly from the general population, suggesting a good degree of generalisability. However, although associations can be drawn from the study results, the cross-sectional design does not prove causality. We are unable to assess the temporal dynamics of SPPB performance with age, nor the prognostic value of SPPB in diagnosing sarcopenia, given the lack of a longitudinal component. Furthermore, study findings cannot be generalised to people living in institutions.