Myosteatosis in the Context of Skeletal Muscle Function Deficit: An Interdisciplinary Workshop at the National Institute on Aging.

Skeletal muscle fat infiltration (known as myosteatosis) is an ectopic fat depot that increases with aging and is recognized to negatively correlate with muscle mass, strength, and mobility and disrupt metabolism (insulin resistance, diabetes). An interdisciplinary workshop convened by the National Institute on Aging Division of Geriatrics and Clinical Gerontology on September 2018, discussed myosteatosis in the context of skeletal muscle function deficit (SMFD). Its purpose was to gain a better understanding of the roles of myosteatosis in aging muscles and metabolic disease, particularly its potential determinants and clinical consequences, and ways of properly assessing it. Special attention was given to functional status and standardization of measures of body composition (including the value of D3-creatine dilution method) and imaging approaches [including ways to better use dual-energy X-ray absorptiometry (DXA) through the shape and appearance modeling] to assess lean mass, sarcopenia, and myosteatosis. The workshop convened innovative new areas of scientific relevance to light such as the effect of circadian rhythms and clock disruption in skeletal muscle structure, function, metabolism, and potential contribution to increased myosteatosis. A muscle-bone interaction perspective compared mechanisms associated with myosteatosis and bone marrow adiposity. Potential preventive and therapeutic approaches highlighted ongoing work on physical activity, myostatin treatment, and calorie restriction. Myosteatosis' impact on cancer survivors raised new possibilities to identify its role and to engage in cross-disciplinary collaboration. A wide range of research opportunities and challenges in planning for the most appropriate study design, interpretation, and translation of findings into clinical practice were discussed and are presented here.

Low testosterone levels and decline in physical performance and muscle strength in older men: findings from two prospective cohort studies.

OBJECTIVE: Progressive declines in serum levels of testosterone parallel the decline in physical performance and muscle strength in ageing men, although findings are not conclusive. We examined whether levels of testosterone were associated with 3-year decline in physical performance and muscle strength in older men. DESIGN: Longitudinal data were available for 486 men (mean age 74.9 years, SD 6.4) from the Longitudinal Ageing Study Amsterdam (LASA) and 1071 well-functioning men (mean age 73.7 years, SD 2.8) from the Health, Ageing and Body Composition (Health ABC) study. MEASUREMENTS: Three-year change in physical performance score and grip strength according to categories of total testosterone (TT) and free testosterone (FT) levels. RESULTS: The mean 3-year change in physical performance was -1.1 (SD 2.7, -13.6%) in LASA and -0.3 (SD 1.5, -2.9%) in Health ABC. The mean 3-year change in grip strength was -9.7 kg (SD 12.2, -13.2%) in LASA and -4.4 kg (SD 11.4,-5.8%) in Health ABC. Low levels of TT were not associated with decline in physical performance or with decline in muscle strength [e.g. mean change in physical performance -1.09 (SD 0.26) in the lowest quartile (Q1) and -0.88 (0.24) in the highest quartile (Q4) of total testosterone in LASA, and -0.26 (0.07) vs.-0.36 (0.11) in Health ABC]. Similar results were found for FT. CONCLUSIONS: Low levels of TT and FT were neither associated with 3-year decline in physical performance nor with 3-year decline in muscle strength in two independent samples of older men.