Fat-free Mass Index Percentiles Across The Lifespan Based On Nhanes Dual-energy X-ray Absorptiometry Data

PURPOSE: Sarcopenia, or age-related muscle tissue and strength loss, begins around age 40 at a rate of 0.5-1.2% mass and 3% strength each year; sarcopenia is one of the most important predictors of falls and fractures, and can lead to loss of independence and quality of life. Low muscle strength is also an independent risk factor for mortality. Unfortunately, there is limited information about population-distributional, longitudinal changes in muscle mass. Foundational work by Kudsk et al. (2016) defined a template for comparing an individual patient’s estimate of fat free mass (FFM, a proxy for muscle mass) with the general US population. METHODS: We revisit this work, and offer a handful of improvements: (i) to estimate FFM we now use the newly available NHANES dual-energy X-ray absorptiometry data (rather than bioimpedance), (ii) we use an improved form of quantile regression, which allows for (ii) the correct use of survey-sampling weights (i.e., improving generalizability to the US population and particularly for statements about the highest and lowest percentiles of FFM), and (iv) we add a statistical description of uncertainty (i.e., confidence bands) to aid in interpreting meaningful changes in FFM. RESULTS: We provide population-based plots of across the lifespan estimates of the quantiles of fat free mass for men and women in the United States (in the form of plots). CONCLUSION: This work is meant to provide useful insights - for clinicians, researchers, and athletes - into how FFM changes through the lifespan.