The impact of old age on skeletal muscle energetics: supply and demand.

Properly functioning skeletal muscle is critical for locomotion and performance of many activities of daily living. Muscle wasting and decreased function of skeletal muscle are important factors in many age-related morbidities. There are several pathways for generating ATP in skeletal muscle that allow adequate ATP supply to meet increased demand during muscle activity. A growing body of literature provides evidence that the aging process may be accompanied by changes in metabolic supply and demand during muscle contractions. Herein, we review a body of evidence that several pathways of ATP synthesis (anaerobic glycolysis, oxidative phosphorylation) may be impaired in aging skeletal muscle as well as several underlying molecular and cellular mechanisms. However, detrimental effects of aging on muscle energy metabolism are not universally accepted, particularly when physical inactivity is accounted for. We discuss this important concept as well as several potential countermeasures that may compress the period of morbidity in old age. In the second half of this review, we discuss how energetic demand of skeletal muscle is affected by aging, with specific focus on basal and contractile ATPase activity.