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Skeletal muscle weakness in old age: underlying mechanisms.
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1994
Year
Muscle FunctionAgingSkeletal Muscle WeaknessMuscle AtrophyMuscle PhysiologyKinesiologyMuscle InjurySkeletal MuscleBiomechanicsPhysical AgingApplied PhysiologyHealth SciencesRehabilitationNeuromuscular PhysiologyPhysiologyExercise PhysiologyMusculoskeletal AgingAge-associated Muscle AtrophyMedicineSarcopenia
Maintenance of muscle mass and strength is essential for mobility and quality of life, yet muscle atrophy, declining strength, and frailty are widely regarded as inevitable with aging, although their causes remain unclear. Clarifying the mechanisms responsible for these changes would improve our understanding of how preventable or treatable they are. Age‑related muscle atrophy and strength loss are largely driven by motor unit remodeling through selective denervation and reinnervation, a process that is exacerbated by increased injury susceptibility and impaired regeneration. Across species, aging reduces muscle force and power by roughly 35 % and 30 % respectively, and old mice show greater injury susceptibility and diminished recovery capacity compared to younger animals.
Maintenance of muscle mass and strength contributes to mobility which impacts on quality of life. Although muscle atrophy, declining strength, and physical frailty are generally accepted as inevitable concomitants of aging, the causes are unknown. Clarification of the mechanisms responsible for these changes would enhance our understanding of the degree to which they are preventable or treatable. The decline in muscle function between maturity and old age is similar for muscles of many different animals including human beings, and is typified by the decreases of approximately 35% in maximum force, approximately 30% in maximum power, and 20% in normalized force (kN.m-2) and power (W.kg-1) of extensor digitorum longus (EDL) muscles in old compared with adult mice. Much of the age-associated muscle atrophy and declining strength may be explained by motor unit remodeling which appears to occur by selective denervation of muscle fibers with reinnervation by axonal sprouting from an adjacent innervated unit. Muscles in old mice appear more susceptible to injury than muscles in young or adult mice and have a decreased capacity for recovery. The process of age-related denervation may be aggravated by an increased susceptibility of muscles in old animals to contraction-induced injury coupled with impaired capacity for regeneration.