Muscle fibre capillarization is a critical factor in muscle fibre hypertrophy during resistance exercise training in older men

Journal of Cachexia, Sarcopenia and Muscle | 04-08-2016|

Abstract:

Background: Adequate muscle fiber perfusion is critical for the maintenance of muscle mass, it is essential in the rapid delivery of oxygen, nutrients and growth factors to the muscle, stimulating muscle fiber growth. Muscle fiber capillarization is known to decrease substantially with advancing age. However, whether (relative) low muscle fiber capillarization negatively impacts the muscle hypertrophic response following resistance exercise training in older adults is unknown.

Methods: Twenty-two healthy older men (71±1 yrs) performed 24 weeks of progressive resistance type exercise training. To assess the change in muscle fiber characteristics, percutaneous biopsies from the vastus lateralis muscle were taken before and following 12 and 24 weeks of the intervention program. A comparison was made between participants who had a relative low type II muscle fiber CFPE (capillary-to-fiber perimeter exchange index; LOW group) and high type II muscle fiber CFPE (HIGH group) at baseline. Type I and type II muscle fiber size, satellite cell, capillary content and distance between satellite cells to the nearest capillary were determined by immunohistochemistry.

Results: Overall, type II muscle fiber size (from 5150±234 to 6719±446 µm², P<0.05) and satellite cell content (from 0.058±0.006 to 0.090±0.010 satellite cells per muscle fiber, P<0.05) had increased significantly in response to 24 weeks of resistance exercise training. However, these improvements where mainly driven by differences in baseline type II muscle fiber capillarization. Whereas muscle fiber size (from 5170±390 to 7133±314µm², P<0.05) and satellite cell content (from 0.059±0.009 to 0.102±0.017 satellite cells per muscle fiber, P<0.05) increased significantly in the HIGH group, no significant changes were observed in LOW group following exercise training. No significant changes in type I and type II muscle fiber capillarization were observed in response to 12 and 24 weeks of resistance exercise training in both the LOW and HIGH group.

Conclusion: Type II muscle fiber capillarization at baseline may be a critical factor for allowing muscle fiber hypertrophy to occur during prolonged resistance exercise training in older men.

Auteurs: Tim Snijders^1,2, Joshua P. Nederveen¹, Sophie Joanisse¹, Marika Leenders², Lex B. Verdijk², Luc J.C. van Loon², Gianni Parise¹

Affiliates: ¹ Department of Kinesiology and Medical Physics & Applied Radiation Sciences, McMaster University, Hamilton, Ontario, Canada L8S 4L8.² NUTRIM School of Nutrition and Translational Research in Metabolism, Maastricht University, Maastricht, the Netherlands.

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