Sarcopenia

The prevalence of sarcopenia was studied in the New Mexico Elder Health Survey, which measured appendicular muscle mass by dual-energy X-ray absorptiometry (DXA) in 883 elderly Hispanic and non-Hispanic white men and women. Sarcopenia was defined as a muscle mass two or more standard deviations below the mean for young healthy participants. The prevalence of sarcopenia by this definition increased from between 13 percent and 24 percent of persons under age seventy to over 50 percent of those over eighty years of age. Sarcopenic women had 3.6 times higher rates of disability, and men 4.1 times higher rates, compared to study participants with normal muscle mass.

Kehayias, et al. (1997) found that the quality of the lean body mass, defined as the ratio of cell mass (the metabolically active portion of the body) to lean mass (cell mass plus extracellular water and connective tissue), declined with age. These data suggest that sarcopenia is universal, and indeed this would be consistent with an age-related phenomenon. It also complements the data of Baumgartner, et al., where a cutoff was used to define sarcopenia. Cross-sectional data also indicate that older persons have a lower amount of type II (fast-twitch, glycolytic) fibers in their muscles than young adults, but that type I (slow-twitch, oxidative) fibers are comparable in number.