Microvascular adaptations to resistance training are independent of load in resistance-trained young men

Abstract

Resistance training promotes microvasculature expansion; however, it remains unknown how different resistance training programs contribute to angiogenesis. Thus, we recruited experienced resistance-trained participants and determined the effect of 12 wk of either high-repetition/low-load or low-repetition/high-load resistance training performed to volitional fatigue on muscle microvasculature. Twenty men performed either a high-repetition [20-25 repetitions, 30-50% of 1-repetition maximum (1RM); n = 10] or a low-repetition (8-12 repetitions, 75-90% of 1RM; n = 10) resistance training program. Muscle biopsies were taken before and after resistance training, and immunohistochemistry was used to assess fiber type (I and II)-specific microvascular variables. High-repetition/low-load and low-repetition/high-load groups were not different in any variable before resistance training. Both protocols resulted in an increase in capillarization. Specifically, after resistance training, the capillary-to-fiber ratio, capillary contacts, and capillary-to-fiber perimeter exchange index were elevated, and sharing factor was reduced. These data demonstrate that resistance training performed to volitional failure, using either high repetition/low load or low repetition/high load, induced similar microvascular adaptations in recreationally resistance-trained young men.

Keywords: capillary; health; resistance training; skeletal muscle.

Figures

Fig. 1.

Representative images of muscle fiber type-specific analyses. A: laminin (blue). B: myosin heavy chain (MHC)-I (green). C: CD31 (red); D: MHC-I (green) + laminin (blue) + CD31 (red). “x” depicts the same fiber followed throughout. Color enhancement of different channels has been performed for visual clarity (i.e., after recording and analysis).

Fig. 2.

Fiber type-specific capillary-fiber index ratio (C/Fi; A and B), capillary contacts (CC; D and E), and capillary-fiber perimeter exchange (CFPE) index (G and H) before (Pre) and after (Post) 12 wk of high-repetition/low-load (n = 10 men) or low-repetition/high-load (n = 10) resistance training and individual percent change in C/Fi (C), CC (F), and CFPE index (I) after training in type I and II fibers. C/Fi, CC, and CFPE were significantly elevated as a result of both training programs. Data are presented as medians (lines) with interquartile ranges (boxes) ± range (minimum and maximum), where + indicates the mean. *Significant main effect of time (P < 0.02) from baseline. †Significantly different from high repetition/low load.

Fig. 3.

Western blot analysis of vascular endothelial growth factor (VEGF; A) and endothelial nitric oxide synthase (eNOS; B) before (Pre) and after (Post) 12 wk of high-repetition/low-load (n = 10) or low-repetition/high-load (n = 10) resistance training. A: 12 wk of both high-repetition/low-load and low-repetition/high-load resistance training resulted in significant increase in VEGF protein in whole muscle homogenate. B: 12 wk of both high-repetition/low-load and low-repetition/high-load resistance training resulted in significant increase in eNOS protein in whole muscle homogenate. C: representative blots. Data are presented as medians (lines) with interquartile ranges (boxes) ± range (minimum and maximum), where + indicates the mean. *Significant main effect of time (P < 0.05).

Fig. 4.

Mitochondrial content of whole muscle homogenate before (Pre) and after (Post) 12 wk of high-repetition/low-load (n = 10) or low-repetition/high-load (n = 10) resistance training. A–D: 12 wk of both high-repetition/low-load and low-repetition/high-load resistance training resulted in no change in oxidative phosphorylation (OXPHOS) protein contents. E: representative blot. Data are presented as medians (lines) with interquartile ranges (boxes) ± range (minimum and maximum), where + indicates the mean.