Aging processes are inevitably accompanied by structural and functional changes in vital organs. Skeletal muscle, which accounts for 40% of total body weight, deteriorates quantitatively and qualitatively with aging. Skeletal muscle is known to play diverse crucial physical and metabolic roles in humans. Sarcopenia is a condition characterized by significant loss of muscle mass and strength. It is related to subsequent frailty and instability in the elderly population. Because muscle tissue is involved in multiple functions, sarcopenia is closely related to various adverse health outcomes. Along with increasing recognition of the clinical importance of sarcopenia, several international study groups have recently released their consensus on the definition and diagnosis of sarcopenia. In practical terms, various skeletal muscle mass indices have been suggested for assessing sarcopenia: appendicular skeletal muscle mass adjusted for height squared, weight, or body mass index. A different prevalence and different clinical implications of sarcopenia are highlighted by each definition. The discordances among these indices have emerged as an issue in defining sarcopenia, and a unifying definition for sarcopenia has not yet been attained. This review aims to compare these three operational definitions and to introduce an optimal skeletal muscle mass index that reflects the clinical implications of sarcopenia from a metabolic perspective.

The concept of sarcopenia has expanded recently to include muscle strength or physical performance. We investigated whether the Europe Working Group on Sarcopenia in Older People (EWGSOP) definition of sarcopenia predicts the risk of all-cause mortality in community-dwelling older adults. This study included 284 men and 272 women aged 65 and older. The outcome was all-cause mortality during the 6-year follow-up period. We defined sarcopenia based on the EWGSOP definitions of sarcopenia: height (ht)- or weight (wt)-adjusted appendicular skeletal muscle mass (ASM/ht² or ASM/wt) assessed by dual-energy x-ray absorptiometry, leg muscle strength, and short physical performance battery test score. During the 6-year follow-up, 40 men and 19 women died. The risk of death was 2.99 times and 3.22 times higher in men with sarcopenia identified by ASM/ht² and ASM/wt, respectively, compared with nonsarcopenic men. The hazard ratio for death was 5.37 for men with weak leg muscle strength. Men with a low short physical performance battery score had a 3.15 times higher risk of death compared with those with high short physical performance battery scores, even after adjusting for all covariates. The adjusted hazard ratios for EWGSOP-defined sarcopenia were 4.00 for ASM/ht² and 6.89 for ASM/wt in men. By contrast, sarcopenia defined by these criteria was not associated with a higher risk of death in women. Our data suggest that, in older men, EWGSOP-defined sarcopenia is related to higher mortality compared with nonsarcopenia regardless of the ASM/ht² or ASM/wt index. In older women, further studies with large sample sizes are needed to assess whether EWGSOP-defined sarcopenia increases the mortality risk.

We evaluate the accuracy of whole body muscle mass (WBMM) and appendicular skeletal muscle mass (ASMM) assessed by bioelectrical impedance analysis (BIA) using an InBody770 machine (InBody, Seoul, Korea) referenced to dual-energy X-ray absorptiometry (DXA) in 507 people (mean age 63.7 ± 10.8 years, body mass index (BMI) 25.2 ± 3.5 kg/m²). Mean WBMMs measured by BIA and DXA were 49.3 ± 6.6 kg and 46.8 ± 6.5 kg in men and 36.1 ± 4.7 kg and 34.0 ± 4.8 kg in women, respectively. The respective effect sizes and 95% confidence intervals (CIs) for the difference were 2.49 (2.22–2.76) for men, and 2.12 (1.91–2.33) for women. Mean ASMMs measured by BIA and DXA were 22.1 ± 3.3 kg and 19.9 ± 3.2 kg in men, and 15.3 ± 2.5 kg and 13.5 ± 2.2 kg in women, respectively. The respective effect sizes and 95% CIs for the difference were 2.26 (2.10–2.41) for men and 1.75 (1.65–1.87) for women. The BIA clearly overestimated WBMM by 2.28 kg and ASMM by 1.97 kg compared with DXA. Using BMI, gender, and fat percentage, we derive equations that improved the residuals to <2 kg between methods from 38.29% to 85.91% for WBMM and 52.78% to 97.02% for ASMM.

Trabecular bone score (TBS) is a novel texture index that evaluates the pixel gray-level variations in lumbar spine dual-energy X-ray absorptiometry images and is related to bone microarchitecture independent of bone mineral density (BMD). We investigated lumbar spine TBS as an indicator for skeletal deterioration in diabetes. Cross-sectional data were collected from subjects participating in an ongoing prospective, community-based, cohort study from 2009 to 2010. We included 1229 men and 1529 postmenopausal women older than 50 years in the Ansung cohort. Biochemical parameters, lumbar spine TBS, and BMD from dual-energy X-ray absorptiometry images were measured. Lumbar spine TBS was lower in men with diabetes than in nondiabetic men (1.287 ± 0.005 vs 1.316 ± 0.003, P < .001), whereas lumbar spine BMD was higher in men with diabetes (1.135 ± 0.010 vs 1.088 ± 0.006 g/cm(2)). Lumbar spine TBS was lower in women with diabetes than in nondiabetic women only in an unadjusted model (1.333 ± 0.004 vs 1.353 ± 0.003). However, women younger than 65 years (n = 707) with diabetes had a lower TBS than those without diabetes, even after adjusted for covariates (P < .001). Diabetes was not associated with BMD at femur sites in both genders. TBS was negatively correlated with glycated hemoglobin, fasting plasma glucose, fasting insulin, and homeostasis model assessment for insulin resistance but not with homeostasis model assessment for β-cell function in both genders. The inverse association between lumbar spine TBS and insulin resistance may make it an indicator for determining skeletal deterioration in diabetic patients who have high BMD.

The study aimed to investigate the influence of hyperglycemia on muscle quality in older men with type 2 diabetes. This was a subsidiary study of the Korean Longitudinal Study of Health and Aging. Among 326 older men consenting to tests of body composition and muscle strength, 269 men were ultimately analyzed after the exclusion because of stroke (n=30) and uncertainty about the diagnosis of diabetes (n=27). Body composition was measured using dual-energy X-ray absorptiometry and computed tomography. Muscle strength for knee extension was measured using an isokinetic dynamometer. Muscle quality was assessed from the ratio of leg strength to the entire corresponding leg muscle mass. The muscle mass, strength, and quality in patients with type 2 diabetes did not differ significantly from controls. However, when patients with diabetes were subdivided according to their glycemic control status, patients with a glycosylated hemoglobin (HbA1c) level of ≥8.5% showed significantly decreased leg muscle quality by multivariate analysis (odds ratio, 4.510; P=0.045) after adjustment for age, body mass index, smoking amount, alcohol consumption, physical activity, and duration of diabetes. Physical performance status was also impaired in subjects with an HbA1c of ≥8.5%. Poor glycemic control in these older patients with diabetes was associated with significant risk of decreased muscle quality and performance status. Glycemic control with an HbA1c of <8.5% might be needed to reduce the risk of adverse skeletal and functional outcomes in this population.