Regulation of fiber size, oxidative potential, and capillarization in human muscle by resistance exercise

Abstract

To examine the hypothesis that increases in fiber cross-sectional area mediated by high-resistance training (HRT) would result in a decrease in fiber capillarization and oxidative potential, regardless of fiber type, we studied six untrained males (maximum oxygen consumption, 45.6 ± 2.3 ml ⋅ kg−1 ⋅ min−1; mean ± SE) participating in a 12-wk program designed to produce a progressive hypertrophy of the quadriceps muscle. The training sessions, which were conducted 3 times/wk, consisted of three sets of three exercises, each performed for 6–8 repetitions maximum (RM). Measurements of fiber-type distribution obtained from tissue extracted from the vastus lateralis at 0, 4, 7, and 12 wk indicated reductions ( P < 0.05) in type IIB fibers (15.1 ± 2.1% vs. 7.2 ± 1.3%) by 4 wk in the absence of changes in the other fiber types (types I, IIA, and IIAB). Training culminated in a 17% increase ( P < 0.05) in cross-sectional area by 12 wk with initial increases observed at 4 wk. The increase was independent of fiber type-specific changes. The number of capillaries in contact with each fiber type increased by 12 wk, whereas capillary contacts-to-fiber area ratios remained unchanged. In a defined cross-sectional field, HRT also increased the capillaries per fiber at 12 wk. Training failed to alter cellular oxidative potential, as measured by succinic dehydrogenase (SDH) activity, regardless of fiber type and training duration. It is concluded that modest hypertrophy induced by HRT does not compromise cellular tissue capillarization and oxidative potential regardless of fiber type.

Regulation of myogenic stem cell behaviour by vessel cells: The "ménage à trois" of satellite cells, periendothelial cells and endothelial cells

“…Several studies have implicated VEGF in skeletal muscle angiogenesis regulation induce by acute aerobic or resistance exercise in both human and animals. [5][6][7][8][9][10][11] Furthermore, it has been shown that training also induce modifications of VEGF mRNA and protein expression. [12][13][14][15][16] Chronic pathological conditions, such as Chronic Obstruction Pulmonary Disease (COPD) and diabetes, 17,18 induce capillary rarefaction suggesting that VEGF is also important in the maintenance of adult skeletal muscle microvasculature.…”

Electrically stimulated resistance training in SCI individuals increases muscle fatigue resistance but not femoral artery size or blood flow

“…6 Short-term high-load resistance training has been shown to evoke increases in not only muscle mass, but also in capillarity, albeit in AB subjects. [7][8][9] The significance of these adaptations is that development of cardiovascular disease and Type II diabetes with SCI may be diminished or delayed by improving the muscles and arteries of individuals with SCI. 10 One potential limitation to NMES training for individuals with SCI is excessive muscle fatigue.…”

Skeletal muscle oxidative function in vivo and ex vivo in athletes with marked hypertrophy from resistance training

“…According to other authors, strength training may increase skeletal muscle efficiency (4) and enhance skeletal muscle "metabolic stability" (50). Other studies reported, after resistance training, unchanged values of maximal O 2 uptake (V O 2 ) (6), as well as unchanged (19) or lower (42,43) mitochondrial volume density, oxidative enzyme activity, and capillary density in the hypertrophic muscles. Thus the specific effects of resistance training, with the related changes in muscle phenotype, on oxidative metabolism appear difficult to reconcile in a unifying scenario.…”