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. 2016;2016:1535367.
doi: 10.1155/2016/1535367. Epub 2016 Sep 19.

Effect of High-Intensity Training in Normobaric Hypoxia on Thoroughbred Skeletal Muscle

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Free PMC article

Effect of High-Intensity Training in Normobaric Hypoxia on Thoroughbred Skeletal Muscle

Hiroshi Nagahisa et al. Oxid Med Cell Longev. .
Free PMC article

Abstract

Hypoxic training is believed to increase endurance capacity in association with hypoxia inducible factor-1α (HIF-1α), a modulator of vascular endothelial growth factor-A (VEGF-A), and to influence activation of satellite cells (SCs). However, the effect of hypoxic training on SC activation and its relation to angiogenesis has not been thoroughly investigated. Eight Thoroughbred horses were subjected to normoxic (FIO2 = 21%) or hypoxic (FIO2 = 15%) training for 3 days/week (100% [Formula: see text]) for 4 weeks. Incremental exercise tests (IET) were conducted on a treadmill under normoxia and the maximal oxygen consumption ([Formula: see text]) and running distance were measured before and after each training session. Muscle biopsy samples were obtained from the gluteus medius muscle at 6 scheduled times before, during, and one week after IET for immunohistochemical analysis and real-time RT-PCR analysis. Running distance and [Formula: see text], measured during IET, increased significantly after hypoxic training compared with normoxic training. Capillary density and mRNA expression related to SC activation (e.g., myogenin and hepatocyte growth factor) and angiogenesis (VEGF-A) increased only after hypoxic training. These results suggest that increases in mRNA expression after training enhance and prolong SC activation and angiogenesis and that nitric oxide plays an important role in these hypoxia-induced training effects.

Conflict of interest statement

The authors declare that they have no competing interests regarding the publication of this paper.

Figures

Figure 1
Figure 1
Schematic figure of the experimental schedule. The training protocol adopted a randomized crossover design, which was separated by a 16-week detraining period. Eight horses were assigned randomly into normoxic training (n = 4, FIO2 = 21%) and hypoxic training (n = 4, FIO2 = 15% O2) groups. Incremental exercise tests (IET) were carried out before (pretest) and after (posttest) training. In each IET, horses were subjected to biopsy sampling of the gluteus medius six times, indicated by “↑” (before (pre) and immediately (post) and 4 hours (4 h), 24 hours (24 h), 3 days (3 d), and 7 days (7 d) after IET).
Figure 2
Figure 2
Typical photomicrographs of serial transverse sections of the gluteus medius muscle. Thicknesses of sections are 7 and 50 μm in panels (a) and (b), respectively. (a) Triple-immunofluorescent stained for laminin (green), Pax7 (red), and nuclei (blue). The white arrow in (a) indicates a satellite cell (Pax7+ nuclei). (b) Single-immunofluorescent stained for laminin. White arrows in (b) indicate capillaries.
Figure 3
Figure 3
Changes in run distance (a) and maximal oxygen consumption (V˙O2max) (b) in the incremental exercise test under normoxia for the normoxic training group (white bar) and the hypoxic training group (black bar). Significant difference versus pretest (p < 0.05). Values are mean ± SEM.
Figure 4
Figure 4
Changes in fiber type population (a), fiber cross-sectional area (b), capillary density (c), and number of satellite cells (d) in pretest of control (Nor Con: normoxic control; Hypo Con: hypoxic control) and posttest (Nor Tr: normoxic training; Hypo Tr: hypoxic training) in normoxic or hypoxic training group. Measurements were performed on muscle samples obtained before the incremental exercise test (pre). White, grey, and black bars in (a), (b), and (d) represent fiber types I, IIa, and IIx, respectively. White and black bars in (c) represent normoxia and hypoxia, respectively. Significant difference versus pretest (p < 0.05). Values are mean ± SEM.
Figure 5
Figure 5
(a–f) Time-course changes in mRNA expression of Pax7 (a), MyoD (b), myogenin (c), VEGF-A (d), KDR (e), and PGC-1α (f) in pretest of control (Nor Con: normoxic control, light red; Hypo Con: hypoxic control, light blue) and posttest (Nor Tr: normoxic training, red; Hypo Tr: hypoxic training, blue) after normoxic or hypoxic training. Measurements were performed before (pre) and immediately (post) and 4 hours (4 h), 24 hours (24 h), 3 days (3 d), and 7 days (7 d) after the incremental exercise test. Values of mRNA expression were calculated as x-fold change from pretest of each control. Significant difference versus pretest (p < 0.05). Values are mean ± SEM. Significant difference versus normoxia training group (p < 0.05). (g–l) Time-course changes in mRNA expression of ANGPT1 (g), HIF-1α (h), HGF (i), FGF-2 (j), IGF-1 (k), and IL-6 (l) in pretest of control (Nor Con: normoxic control, light red; Hypo Con: hypoxic control, light blue) and posttest (Nor Tr: normoxic training, red; Hypo Tr: hypoxic training, blue) after normoxic or hypoxic training. Measurements were performed before (pre) and immediately (post) and 4 hours (4 h), 24 hours (24 h), 3 days (3 d), and 7 days (7 d) after the incremental exercise test. Values of mRNA expression were calculated as x-fold change from pretest of each control. Significant difference versus pretest (p < 0.05). Values are mean ± SEM. Significant difference versus normoxic training group (p < 0.05).

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