Fibre-type composition, structure and cytoskeletal protein location of fibres in anterior tibial muscle

Abstract

Muscle biopsies were obtained from the anterior tibial muscle (TA) of 15 healthy, sedentary young (23-37 years) and 13 healthy and physically active elderly (66-77 years) volunteers. The mean frequency of type I fibres was lower in the young subjects compared with the elderly, but the mean type I fibre cross-sectional area was equal in the two groups. The type IIA fibres were, however, smaller in the elderly than in young subjects. Capillary density, capillary per fibre ratio, capillaries in contact with type I fibres (CC) and CC in relation to type I and type II fibre area did not differ in the two groups. The number of capillaries in contact with type IIA fibres was higher in the younger group. Only occasional and minor pathological changes were observed in the young subjects. In the elderly, such changes were much more common, including central nuclei, ring fibres, fibre splitting, scattered highly atrophic fibres, moth-eaten fibres and vacuoles. Ring fibres were most easily identified with anti-desmin labelling and highly atrophic fibres exhibited a rough network of labelling. Increased content of actin and spectrin was also observed at the periphery of ring fibres. In the elderly group, a qualitative ultrastructural analysis was also obtained and obvious changes included some myofilament loss, collections of lipofuscin which were also observed in satellite cells, proliferation of the SR-T systems and increased wrinkling of nuclear membranes and sarcolemma.

Peripheral impairments cause a progressive age-related loss of strength and velocity-dependent power in the dorsiflexors

“…Potential alterations at the periphery responsible for the decrease in contraction velocity include increased percentages of type I muscle fibers (28,29), increased expression of slow myosin heavy chain (MHC) isoforms (28,29), increased internal drag produced by increased connective tissue in the muscle and structural changes to the myosin filaments (29), decreases in fiber fascicle length due to a reduction in the number of sarcomeres in series (22), and alterations to the excitation-contraction complex (7,11). Although there is some experimental evidence to support age-related increases in the percentage of type I muscle fibers (6,14) and the relative proportion of slow MHC isoforms (3,23), the impact of these factors would be relatively minor in the dorsiflexors considering the predominance (ϳ80%) of type I fibers in the young (4,6).…”

Heterogeneous effects of old age on human muscle oxidative capacity in vivo: a systematic review and meta-analysis

“…To date, there is a lack of sufficient data examining changes in perfusion and oxidative capacity of muscle in aging to permit a formal analysis of perfusion as a moderator of age-related changes in muscle oxidative capacity in vivo. Likewise, muscle fiber composition may change toward a slower phenotype with age (Jakobsson et al 1990;Lexell et al 1988), habitual PA decreases across the lifespan (Troiano et al 2008), and aerobic fitness is lower in old age (Proctor and Joyner 1997). As such, these factors, and others, may impact age-related changes in muscle oxidative capacity.…”

Specific force of the rat plantaris muscle changes with age, but not with overload

“…This cannot be explained by a change in the relative amount of non-contractile tissue during this period. Supposedly, the cause may be an incom plete reinnervation o f previously denervated fibres, during the denervation-reinnervation process at advanced age [6], or the occurrence o f myofilament loss as found in human tibialis anterior muscle [7], The difference in specific force, expressed as tetanic force/muscle weight, between m. plantaris o f 5-and 25-month-old rats disappeared, when expressed as tetanic force per total muscle cross-sectional area, whether corrected for the relative amount o f non-contractile tissue or not. Larsson and Edstrom [8] reported a decrease in tetanic force per muscle weight in tibialis anterior muscle of rats between 6 and 2 0 -2 4 months o f age, while the force per total muscle fibre cross-sectional area displayed no significant change.…”