While endurance exercise training promotes angiogenesis and improves metabolic health, the effect of resistance training on this process is less well defined. We hypothesised that capillarization would increase proportionally, and concurrently, with muscle fiber hypertrophy in response to resistance training in young men.
Methods: In this double blind, randomized control trial, 36 males (22 +/- 1 y) were randomized to placebo or protein supplementation, and participated in 12-wk of resistance training. Skeletal muscle biopsies were collected prior to, and following 2, 4, 8, and 12-wk of training. Immunohistochemistry assessed fiber-type specific size and capillarization. Western blot and RT-PCR assessed proteins involved in the molecular regulation of angiogenesis.
Results: Resistance training effectively increased type I (15 +/- 4%; P<0.01) and type II fiber cross-sectional area (CSA; 28 +/- 5%; P<0.0001), an effect that tended to be further enhanced with protein supplementation in type II fibers (P=0.078). Capillary-to-fiber ratio significantly increased in type I (P=0.001) and II (P=0.015) fibers after 12-wk of resistance exercise training, and was evident after only 2-wk. Capillary-to-fiber perimeter exchange index increased in the type I fibers only (P=0.054) following 12-wk of training. Training resulted in a reduction in VEGF mRNA. A (P=0.008), while VEGFR2 (P=0.016), HIF1[alpha] (P=0.016) and eNOS (P=0.01) increased in both groups. HIF1[alpha] protein content was higher in the protein group (main group effect P=0.02) and eNOS content demonstrated a divergent relationship (time x group interaction P=0.049).
Conclusions: This study presents novel evidence that microvascular adaptations, and the molecular pathways involved, are elevated following 2-wk of a 12-wk resistance training program. Increases in muscle fiber CSA are effectively matched by the changes in the microvasculature, providing further support for resistance training programs to optimize metabolic health.
(C) 2017 American College of Sports Medicine