Sv. Brooks et Ja. Faulkner, SKELETAL-MUSCLE WEAKNESS IN OLD-AGE - UNDERLYING MECHANISMS, Medicine and science in sports and exercise, 26(4), 1994, pp. 432-439
Maintenance of muscle mass and strength contributes to mobility which
impacts on quality of life. Although muscle atrophy, declining strengt
h, and physical frailty are generally accepted as inevitable concomita
nts of aging, the causes are unknown. Clarification of the mechanisms
responsible for these changes would enhance our understanding of the d
egree to which they are preventable or treatable. The decline in muscl
e function between maturity and old age is similar for muscles of many
different animals including human beings, and is typified by the decr
eases of similar to-35% in maximum force, similar to 30% in maximum po
wer, and 20% in normalized force (kN.m(-2)) and power (W.kg(-1)) of ex
tensor 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 select
ive denervation of muscle fibers with reinnervation by axonal sproutin
g from an adjacent innervated unit. Muscles in old mice appear more su
sceptible to injury than muscles in young or adult mice and have a dec
reased capacity for recovery. The process of age-related denervation m
ay be aggravated by an increased susceptibility of muscles in old anim
als to contraction-induced injury coupled with impaired capacity for r
egeneration.