From muscle wasting to sarcopenia and myopenia: update 2012

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Abstract
Human muscle undergoes constant changes. After about age 50, muscle mass decreases at an annual rate of 1–2 %. Muscle strength declines by 1.5 % between ages 50 and 60 and by 3 % thereafter. The reasons for these changes include denervation of motor units and a net conversion of fast type II muscle fibers into slow type I fibers with resulting loss in muscle power necessary for activities of daily living. In addition, lipids are deposited in the muscle, but these changes do not usually lead to a loss in body weight. Once muscle mass in elderly subjects falls below 2 standard deviations of the mean of a young control cohort and the gait speed falls below 0.8 m/s, a clinical diagnosis of sarcopenia can be reached. Assessment of muscle strength using tests such as the short physical performance battery test, the timed get‐up‐and‐go test, or the stair climb power test may also be helpful in establishing the diagnosis. Serum markers may be useful when sarcopenia presence is suspected and may prompt further investigations. Indeed, sarcopenia is one of the four main reasons for loss of muscle mass. On average, it is estimated that 5–13 % of elderly people aged 60–70 years are affected by sarcopenia. The numbers increase to 11–50 % for those aged 80 or above. Sarcopenia may lead to frailty, but not all patients with sarcopenia are frail—sarcopenia is about twice as common as frailty. Several studies have shown that the risk of falls is significantly elevated in subjects with reduced muscle strength. Treatment of sarcopenia remains challenging, but promising results have been obtained using progressive resistance training, testosterone, estrogens, growth hormone, vitamin D, and angiotensin‐converting enzyme inhibitors. Interesting nutritional interventions include high‐caloric nutritional supplements and essential amino acids that support muscle fiber synthesis.