While most older adults consider themselves to be in good health and live independent lives, the National Advisory Council on Aging has reported staggering numbers regarding diminished health status in aging adults, with more than 90% having a chronic health condition. Frailty, and chronic health conditions, can be attributed to a decline across multiple physiological systems, resulting in a reduction of one''s ability to complete tasks of everyday living. Sarcopenia (muscle loss) can start as early as middle age and can continue to accelerate throughout life. Past techniques that have been used to classify sarcopenia have used various body composition methods to estimate muscle mass. However, there has not been an investigation looking at how well multiple sarcopenia classification methods agree or if alternative body composition methods can be used in place of the current methods. This book examines the validity of several body composition techniques used in older adults compared to a criterion four-compartment model and dual-energy X-ray absorptiometry. Additionally, this book compares two body composition-based methods for the classification of sarcopenia.