Low skeletal muscle capillarization limits muscle adaptation to resistance exercise training in older adults

Adequate muscle perfusion supports the transport of nutrients, oxygen and hormones into muscle fibers. Aging is associated with a substantial decrease in skeletal muscle capillarization, fiber size and oxidative capacity, which may be improved with regular physical activity. The aim of this study wa...

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Bibliographic Details
Published in:	Experimental gerontology Vol. 127; p. 110723
Main Authors:	Moro, Tatiana, Brightwell, Camille R., Phalen, Danielle E., McKenna, Colleen F., Lane, Samantha J., Porter, Craig, Volpi, Elena, Rasmussen, Blake B., Fry, Christopher S.
Format:	Journal Article
Language:	English
Published:	England Elsevier Inc 01-11-2019
Subjects:	Aging Capillary Fiber cross-sectional area Muscle hypertrophy Muscle protein synthesis Muscle hypertrophy Aging Fiber cross-sectional area Muscle protein synthesis Capillary
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Summary:	Adequate muscle perfusion supports the transport of nutrients, oxygen and hormones into muscle fibers. Aging is associated with a substantial decrease in skeletal muscle capillarization, fiber size and oxidative capacity, which may be improved with regular physical activity. The aim of this study was to investigate the relationship between muscle capillarization and indices of muscle hypertrophy (i.e. lean mass; fiber cross sectional area (CSA)) in older adults before and after 12 weeks of progressive resistance exercise training (RET). Interventional study 19 subjects (10 male and 9 female; 71.1 ± 4.3 years; 27.6 ± 3.2 BMI) were enrolled in the study and performed a whole body RET program for 12 weeks. Subjects where then retrospectively divided into a LOW or HIGH group, based on their pre-RET capillary-to-fiber perimeter exchange index (CFPE). Physical activity level, indices of capillarization (capillaries-to-fiber ratio, C:Fi; CFPE index and capillary-to-fiber interface, LC-PF index), muscle hypertrophy, muscle protein turnover and mitochondrial function were assessed before and after RET. Basal capillarization (C:Fi; CFPE and LP-CF index) correlates with daily physical activity level (C:Fi, r = 0.57, p = 0.019; CFPE index, r = 0.55, p = 0.024; LC-PF index, r = 0.56, p = 0.022) and CFPE and LC-PF indices were also positively associated with oxidative capacity (respectively r = 0.45, p = 0.06; r = 0.67, p = 0.004). Following RET, subjects in the HIGH group underwent hypertrophy with significant improvements in muscle protein synthesis and muscle fiber CSA (p < 0.05). However, RET did not promote muscle hypertrophy in the LOW group, but RET significantly increased muscle capillary density (p < 0.05). Muscle fiber capillarization before starting an exercise training program may be predictive of the muscle hypertrophic response to RET in older adults. Increases in muscle fiber size following RET appear to be blunted when muscle capillarization is low, suggesting that an adequate initial capillarization is critical to achieve a meaningful degree of muscle adaptation to RET.
Bibliography:	ObjectType-Article-2 SourceType-Scholarly Journals-1 ObjectType-Feature-1 content type line 23
ISSN:	0531-5565 1873-6815
DOI:	10.1016/j.exger.2019.110723