Sarcopenia: prevalence, mechanisms, and functional consequences.

Aging is associated with significant decline in neuromuscular function and performance. Sarcopenia, often defined as age-related loss of muscle mass, strength, and functional decline, is the most characteristic feature of age-related changes in the neuromuscular system. Strength decline in upper and lower limb muscles is typically 20-40% by the 7th decade and greater in older adults. This is accompanied by similar losses of limb muscle cross-sectional area. Whole body or appendicular muscle mass determination has become the method of choice for defining sarcopenia. Large population studies have reported that sarcopenia affects over 20% of 60- to 70-year-olds, and approaches 50% in those over 75 years. While loss of muscle mass explains a significant component of weakness, other factors are emerging as important contributors. In particular changes at the level of the motor neuron and motor unit are discussed. Muscle power has emerged as an important indicator of function in older adults, and we discuss knee osteoarthritis as a model of accelerated limb sarcopenia.