Abstract
BackgroundAs muscle capillarization is related to the oxidative capacity of the muscle and the size of muscle fibres, capillary rarefaction may contribute to sarcopenia and functional impairment in older adults. Therefore, it is important to assess how ageing affects muscle capillarization and the interrelationship between fibre capillary supply with the oxidative capacity and size of the fibres.MethodsMuscle biopsies from healthy recreationally active young (22 years; 14 men and 5 women) and older (74 years; 22 men and 6 women) people were assessed for muscle capillarization and the distribution of capillaries with the method of capillary domains. Oxidative capacity of muscle fibres was assessed with quantitative histochemistry for succinate dehydrogenase (SDH) activity.ResultsThere was no significant age‐related reduction in muscle fibre oxidative capacity. Despite 18% type II fibre atrophy (P = 0.019) and 23% fewer capillaries per fibre (P < 0.002) in the old people, there was no significant difference in capillary distribution between young and old people, irrespective of sex. The capillary supply to a fibre was primarily determined by fibre size and only to a small extent by oxidative capacity, irrespective of age and sex. Based on SDH, the maximal oxygen consumption supported by a capillary did not differ significantly between young and old people.ConclusionsThe similar quantitative and qualitative distribution of capillaries within muscle from healthy recreationally active older people and young adults indicates that the age‐related capillary rarefaction, which does occur, nevertheless maintains the coupling between skeletal muscle fibre size and capillarization during healthy ageing.
Highlights
The microcirculation plays a crucial role in the delivery of oxygen, nutrients, and hormones to, and removal of heat, metabolites, and waste products from, muscle fibres
There were no significant differences between fibre types, sex, or age in the fibre size variation, reflected by SD fibre cross-sectional area (FCSA) (Table 2)
The similar quantitative and qualitative distribution of capillaries within muscles from healthy recreationally active older people and young adults indicates that the age-related capillary rarefaction is not random, but maintains the coupling between skeletal muscle fibre size and capillarization during healthy ageing
Summary
The microcirculation plays a crucial role in the delivery of oxygen, nutrients, and hormones to, and removal of heat, metabolites, and waste products from, muscle fibres. Even at the level of the single fibres, a positive relationship between the mitochondrial volume density and number of capillaries supplying a fibre has been reported.[4] Other studies have shown that the number of capillaries per fibre is positively related to fibre size.[5,6,7] The coupling between fibre size and capillaries per fibre is further emphasized by the similar time course of hypertrophy and angiogenesis during the development of hypertrophy.[8] Given these observations, one might expect that the age-related decreases in fibre size and oxidative capacity are associated with capillary rarefaction. As muscle capillarization is related to the oxidative capacity of the muscle and the size of muscle fibres, capillary rarefaction may contribute to sarcopenia and functional impairment in older adults. It is important to assess how ageing affects muscle capillarization and the interrelationship between fibre capillary supply with the oxidative capacity and size of the fibres
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