Coupling between skeletal muscle fiber size and capillarization is maintained during healthy aging

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.

Low‐load resistance exercise during inactivity is associated with greater fibre area and satellite cell expression in older skeletal muscle

“…We observed a trend ( P = 0.06 and 0.09 for type I and II fibres, respectively) for a greater capillary contact per muscle fibre in the SR + RE compared with the SR leg during step reduction. Immobilization may decrease whereas resistance exercise can increase muscle capillarization, which collectively may function to maintain a constant capillary density . Thus, the difference between the SR and SR + RE legs may be related to the angiogenic nature of the LLRE stimulus in the SR + RE leg and/or an inactivity‐induced contraction of the capillary network in the SR leg.…”

“…Immobilization may decrease 43 whereas resistance exercise can increase muscle capillarization, 29 which collectively may function to maintain a constant capillary density. 44,45 Thus, the difference between the SR and SR + RE legs may be related to the angiogenic nature of the LLRE stimulus in the SR + RE leg and/or an inactivity-induced contraction of the capillary network in the SR leg. The slightly greater capillarization in SR + RE compared with SR leg is notable given that the apparent difference is of similar magnitude as the age-induced changes over~12 years.…”

Failure to expand the motor unit size to compensate for declining motor unit numbers distinguishes sarcopenic from non‐sarcopenic older men

“…; Barnouin et al . ) we can be confident that the increase in MUPs from young to non‐sarcopenic and pre‐sarcopenic men is due to increased motor unit size rather than increased fibre CSA or circumference.…”

Daily muscle stretching enhances blood flow, endothelial function, capillarity, vascular volume and connectivity in aged skeletal muscle

“…; Barnouin et al . ) in skeletal muscle. Exercise training, even initiated in late life, enhances endothelium‐dependent dilatation (Spier et al .…”

“…Ageing alters muscle blood flow during exercise, independent of changes in cardiac output, resulting in a mismatch between oxygen supply and demand (Rodeheffer et al 1984;Delp et al 1998;Behnke et al 2012). Ageing-induced alterations of muscle blood may be linked to the impairment of endothelium-dependent vasodilatation of resistance arteries (Muller- Delp et al 2002) or changes in muscle capillarity, which are dependent on fibre size and oxidative capacity (Hepple & Vogell, 2004;Groen et al 2014;Barnouin et al 2017) in skeletal muscle. Exercise training, even initiated in late life, enhances endothelium-dependent dilatation (Spier et al 2004(Spier et al , 2007, increases capillarity (Charifi et al 2004;Jensen et al 2004), and improves blood flow distribution and capacity in the aged lower limb (Behnke et al 2012).…”