Skeletal muscle and aging.

Age-related changes in muscle mass (sarcopenia) and functional properties are the result of a very complex hierarchical system of basic cell aging processes and cell adaptive responses. A basic aging mechanism pertains to mitochondrial production of free radicals and their associated secondary effects. From this basic aging mechanism many other cellular changes can be explained as direct effects or compensatory changes. Altered skeletal muscle cell biochemical and functional properties during aging resulting from intrinsic mechanisms and from changes in hormonal or local signals that influence phenotype maintenance, are reviewed. The effect of skeletal muscle cell senescence on the cellular response to exercise, and the effect of dietary restriction on muscle cell senescence can also be explored from this perspective.