Sarcopenia has become of great interest and focus of many studies since this phenomenon affects many people. Moreover, sarcopenia is associated with two more pandemic phenomena: frailty and obesity. These health-related conditions are increasing in western countries in general and in the older population in particular. Each of such health conditions relates to functional decline, yet the combination of two or three of them in one person severely affects quality of life and longevity. Aged individuals who are less physically active are more likely to develop sarcopenic obesity, and those who are obese with muscle weakness and inactive are disposed to become frail individuals. Hence, frailty and obesity overlap profoundly with the physical manifestations of sarcopenia of aging. These “unhappy” triads encompasses a wider range of geriatric decline that also includes cognitive, psychology and social deterioration associated with adverse outcomes. Nevertheless, this chapter focuses only on sarcopenia and will review the pathophysiological background of age-related decline in muscle mass and strength.