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

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% truenormalV˙normalOnormal2normalmnormalanormalx) for 4 weeks. Incremental exercise tests (IET) were conducted on a treadmill under normoxia and the maximal oxygen consumption (truenormalV˙normalOnormal2normalmnormalanormalx) 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 truenormalV˙normalOnormal2normalmnormalanormalx, 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.

The effects of moderate intensity training in a hypoxic environment on transcriptional responses in Thoroughbred horses

“…The primer sequences were designed in the laboratory and synthesized by Generay Biotech (Generay, China) based on the mRNA sequences obtained from the NCBI database (listed in Table 3 ). The levels of expression for the mRNAs (cycle threshold, Ct) were normalized to the internal reference glyceraldehyde 3-phosphate dehydrogenase (GAPDH) to obtain ΔCt (Ct of the target – Ct of internal reference) ( Dundas and Ling, 2012 ; Nagahisa et al, 2016 ; Tariq et al, 2016 ). The housekeeping gene GAPDH appeared to be stable in this study, with the coefficient of variance of 4.9%.…”

“…The quest for more effective and efficient training methods that result in optimal performance outcomes is a continuing area of interest in both human and equine fields, and in accordance with this, hypoxic training methods have been the focus of considerable scientific investigations on human athletes for several decades. However, to date only a small number of reports is available in the literature that have examined the physiological and transcriptional responses to hypoxia training in horses ( Greene and Wickler, 2000 ; Nagahisa et al, 2016 ; Wickler and Anderson, 2000 ).…”

“…The hypoxic training method used in horses partially simulates the ‘training high, living low’ approach used in human athletes. Despite some knowledge regarding the efficacy of hypoxia training for enhancing performance in the human athlete remaining debatable, the use of hypoxia training for equine athletes is increasing in popularity ( Nagahisa et al, 2016 ; Rogers, 2013 ). The advent of these chambers necessitates further investigation of this training method before their use for training Thoroughbred horses can be advocated.…”

“…In this study we investigated the transcriptional changes of selected genes which have been shown to be linked to aerobic performance: VEGF, HIF-1α, peroxisome proliferator-activated receptor gamma (PPARγ), peroxisome proliferator-activated receptor gamma co-activator 1-alpha (PGC-1α), cytochrome c oxidase subunit I (COX1), and cytochrome c oxidase subunit IV (COX4) ( Eivers et al, 2010 ; Nagahisa et al, 2016 ; Zoll et al, 2006 ); glucose metabolism: lactate dehydrogenase (LDH), PFK, adenylate kinase (AK3), and pyruvate kinase muscle (PKm) ( Abe et al, 2015 ; Greene and Wickler, 2000 ; Lundby et al, 2009 ); and oxidative stress: super oxide dismutase 2 (SOD-2) ( Chung et al, 2005 ), in an endeavour to provide more insight into the potential impact of the hypoxic stimuli on Thoroughbred horses.…”

Influence of hypoxic stimulation on angiogenesis and satellite cells in mouse skeletal muscle

“…A hypoxic environment [ 1 ] and exercise stimulation [ 2 ] are factors that increase reactive oxygen species (ROS), and hypoxic training combining these may markedly increase ROS [ 3 ]. Increases in ROS and reactive nitrogen species (RNS) may be necessary to acquire beneficial effects of exercise through hormesis effects of ROS and RNS on mitochondrial biosynthesis, angiogenesis and satellite cell (SC) activation [ 4 , 5 ]. We previously demonstrated the beneficial effects of hypoxic training using thoroughbreds, but the capillary density was evaluated only in the gluteus medius muscle, which is a glycolytic metabolism-dominant fast twitch muscle [ 4 ].…”