Fibre-type composition, structure and cytoskeletal protein location of fibres in anterior tibial muscle. Comparison between young adults and physically active aged humans.

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.