Eccentric contraction-induced injury to type I, IIa, and IIa/IIx muscle fibers of elderly adults

Abstract

Muscles of old laboratory rodents experience exaggerated force losses after eccentric contractile activity. We extended this line of inquiry to humans and investigated the influence of fiber myosin heavy chain (MHC) isoform content on the injury process. Skinned muscle fiber segments, prepared from vastus lateralis biopsies of elderly men and women (78± 2 years, N=8), were subjected to a standardized eccentric contraction (strain, 0.25 fiber length; velocity, 0.50 unloaded shortening velocity). Injury was assessed by evaluating pre-and post-eccentric peak Ca 2+ -activated force per fiber cross-sectional area (F max ). Over 90% of the variability in post-eccentric F max could be explained by a multiple linear regression model consisting of an MHC-independent slope, where injury was directly related to pre-eccentric F max , and MHC-dependent y-intercepts, where the susceptibility to injury could be described as type IIa/IIx fibers>type IIa fibers>type I fibers. We previously reported that fiber type susceptibility to the same standardized eccentric protocol was type IIa/IIx>type IIa=type I for vastus lateralis fibers of 25-year-old adults (Choi and Widrick, Am J Physiol Cell Physiol 299:C1409-C1417, 2010). Modeling combined data sets revealed significant age by fiber type interactions, with posteccentric F max deficits greater for type IIa and type IIa/ IIx fibers from elderly vs. young subjects at constant pre-eccentric F max . We conclude that the resistance of the myofilament lattice to mechanical strain has deteriorated for type IIa and type IIa/IIx, but not for type I, vastus lateralis fibers of elderly adults.

Force-Generation Capacity of Single Vastus Lateralis Muscle Fibers and Physical Function Decline With Age in African Green Vervet Monkeys

“…The specific force recorded in this study ranged from 67 to 138 kN/m 2 , in good agreement with previous studies conducted under similar experimental conditions in humans (21,22,49,50). Unloaded shortening velocity (V o ) was inversely related to species body mass, as previously observed in humans, monkeys, rats, and horses (48,51).…”

Effects of aging, exercise, and disease on force transfer in skeletal muscle

“…Force transmission is fundamental to muscle function, maintaining sarcolemmal integrity, and protection from contraction-induced muscle injury. There is, however, limited research on how force transmission proteins respond to exercise and how much they contribute to the loss of strength and increased susceptibility to contraction-induced muscle injury during aging (13,18,50). A better understanding of the components within muscle that transfer force will aid in reducing muscle injury and maintaining muscle strength, resulting in better quality of life for the elderly.…”

The Effects of Short-term Exercise Training on Peak-Torque Are Time- and Fiber-Type Dependent

“…However, because the myofilament lattice is the site where the injury process is thought to originate (43), the possibility still exists that fiber-specific differences in the structure proteins are key in the mechanism of muscle damage. This is because eccentric exercise caused more damage in those chemically skinned human vastus lateralis muscle fibers, which had an abundance of MHC IIa/IIx but not MHC type I, suggesting that the damaged fibers have myofilament weakness (6).…”

“…For example, there is an emerging hypothesis that muscle weakness in old age is the result of an exaggerated susceptibility to contraction-induced injury and the subsequent inability to fully recover from these injuries and that some form of eccentric exercise is effective to combat this weakness (6,21,24,32,34). There is also anecdotal and experimental evidence that highly trained athletes incorporate in their conditioning program eccentrically biased exercises (49).…”