Microcirculatory Changes and Disuse Are Cause of Damage to Muscle Fibres During Aging

Aging induces histological, enzyme-histochemical and ultrastructural changes in skeletal muscle fibres as atrophy, myopathic alterations and damage of the fibre type regulation. Reduction of the physical activity induces fibre atrophy and mitochondrial alterations with decline in mitochondrial oxidations. Muscle fascicles are reduced in size and perifascicular fatty infiltration is evident. Some fibres show degeneration and necrosis. Preferential atrophy of type 2 fibres is evident in the oldest subjects. Changes in almost all ultrastructural components of muscle fibres are evident. Occasional derangement of the myofibrillar apparatus, rod formation, numerical reduction and alterations of mitochondria, increase in sarcoplasmic lipid droplets and proliferation of endogenous lysosomes are frequently observed. Microvascular changes in aging muscle are characterized by thickening and duplication of the basement membrane, and by increased thickness of the muscular layer in small arteries. These alterations result in loss of oxygen flux and energy supply, which induce degenerative myopathic changes in the aging muscle.