Calf circumference measured by trained personnel in the standing position has good discriminatory ability for sarcopenia case-finding amongst healthy community-dwelling older persons⁵⁾ although the diagnostic performance may be attenuated in SO due to decreased sensitivity and resultant underdetection.⁶⁾ The Yubi-Wakka (YW) or finger-ring test, an alternative to calf circumference measurement, is a self-administered, low cost and practicable screening test with good diagnostic performance for sarcopenia. It was assessed to be a valid screening test in comparison to the actual measurement of skeletal muscle mass index.⁷⁾ However, it is unclear whether the diagnostic performance of YW differs between sarcopenia and SO. As an important marker of SO, it is important to understand whether abdominal obesity affects the diagnostic performance of YW.⁴⁾ Thus, this study was conducted to determine the influence of abdominal obesity on the diagnostic performance of YW for sarcopenia identification amongst healthy community-dwelling older adults.

This cross-sectional study used the data of the second follow-up visit of healthy community-dwelling older adults from the longitudinal cohort study “Longitudinal Assessment of Biomarkers for characterisation of early Sarcopenia and Osteosarcopenic Obesity in predicting frailty and functional decline in community-dwelling Asian older adults Study” (GeriLABS-2) (n=230).⁸⁾ Amongst 193 participants who completed the assessment, we excluded four who did not complete evaluation for body composition using bioelectrical impedance analysis, one who could not perform the YW test due to index finger amputation, and one with missing data, resulting in our final sample of 187 (81.3%). Calf circumference was measured by a trained research assistant (both calves in sitting and standing positions) and self-administered YW test performed by making a ring with the index fingers and thumbs of both hands circling the thickest part of the non-dominant calf with the participant’s knee bent at a 90° angle compared with finger-ring circumference.⁹⁾ A positive YW test result is indicated by a “smaller” calf size compared to finger ring circumference. Abdominal obesity was defined using the Asia-Pacific Consensus by the International Diabetes Federation Consensus Worldwide Definition of the Metabolic Syndrome cutoffs for waist circumference (WC; female >80 cm, male >90 cm).¹⁰⁾ The primary outcome measures were the Asian Working Group for Sarcopenia (AWGS) 2019 consensus diagnosis of the presence of either weak handgrip strength (male <28 kg, female <18 kg) or slow gait speed (<1.0 m/s)¹¹⁾ and low appendicular lean mass (ALMI) as measured using dual-energy X-ray absorptiometry (male <7.0 kg/m², female <5.4 kg/m²). This study only considered Sarcopenia.

Area under the receiver operating characteristic curve (AUC) was performed to compare the diagnostic performance for sarcopenia between high versus low WC for both calf circumference and YW. Statistical analyses were performed using IBM SPSS Statistics for Windows, version 23.0 (IBM Corp., Armonk, NY, USA). Statistical tests used were two-tailed, with the level of significance set at 5% (p<0.05).

The mean age was 66.8±7.0 years with Chinese (93.6%) and female (73.3%) predominance. The high scores for basic and instrumental activities of daily living (ADL) (mean scores of 100 and 23, respectively), Frenchay Activities Index (30.97±4.6) and Mini-Nutritional Assessment (27.52±1.8) attested to the relatively robust health of the study participants. Based on body mass index (BMI) and WC to measure obesity, mean BMI was 23.36±3.2 kg/m² and 45 participants (24.1%) have high WC (WC >90 cm in male and >80 cm in female). Participants with high WC were older; had a higher proportion of females and comorbidities such as hypertension and hyperlidemia; and performed poorer on tests of physical performance and muscle strength (Supplementary Table S1). Compared to sarcopenia prevalence of 24.1% (AWGS 2019 criteria), screen-positive rates were 23.5%–34.2% for calf circumference and 16.6% for YW. Compared to calf circumference measurements, YW showed lower discriminatory ability for sarcopenia diagnosis (AUC: 0.515 vs. 0.778–0.825) and low ALMI (AUC: 0.568 vs. 0.814–0.849) in participants with high WC (Table 1). Moreover, YW showed a trend for lower discriminatory ability for sarcopenia diagnosis (AUC: 0.515 vs. 0.683; p=0.093) and low ALMI (AUC: 0.568 vs. 0.726; p=0.054) in high WC compared with low WC, due to lower sensitivity (45.8% vs. 76.2%) for sarcopenia diagnosis and lower specificity (43.4% vs. 68.2%) for low ALMI. There was no difference in YW cutoffs for high versus low WC groups (sarcopenia diagnosis, 33 cm; low ALMI, 34 cm).

Taken together, our results demonstrate the lower diagnostic performance of YW in older persons with high WC due to differential effects on sensitivity for sarcopenia diagnosis and specificity for low muscle mass. This indicates that YW may be less useful as a self-administered screening tool for detecting SO in community-dwelling older adults. Our results are consistent with a recent Asian study which reported that YW may have decreased sensitivity and specificity for sarcopenia case detection compared with calf circumference measurements amongst healthy community-dwelling older persons (BMI 23.4±3.2 kg).¹²⁾ Although the lower limbs hold most of the skeletal muscles and lower fat mass than other body sites, making it the preferred site in anthropometric measurement to assess skeletal muscle mass,¹³⁾ the calf region is composed of skin fold, subcutaneous fat, bone and muscle, which may be affected by factors such as lifestyle, environment, genetics and ethnicity. To circumvent the confounding influence of obesity on the diagnostic performance of calf circumference, it has been proposed that calf skin fold thickness measurement can be subtracted from calf circumference measurements to derive a surrogate measure of calf muscle circumference.¹⁴⁾ However, the YW self-administered test on its own does not distinguish subcutaneous or intramuscular fat from muscle,¹⁵⁾ accounting for the lower diagnostic performance due to decreased sensitivity for sarcopenia diagnosis and decreased specificity for low ALMI detection in older adults with high WC observed in our study. Limitations of the study using a cross-sectional design with a small sample size should be addressed by future large prospective studies that may further evaluate the case-finding ability and predictive validity of YW in community-dwelling older persons with SO.