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

Abstract

This study investigated the effects of six weeks of normobaric hypoxic training on transcriptional expression of the genes associated with mitochondrial and glycolytic activities in Thoroughbred horses. Eight horses were divided into two groups of four. They completed an identical incremental, moderate intensity training program, except that one group trained in a hypoxic chamber with 15% oxygen for 30 min on alternate days except Sundays (HT), while the other group trained in normal air (NC). Prior to and post training, heart rate and blood lactate were measured during an incremental treadmill test. Muscle biopsy samples were taken prior to and 24 h post the training period for qPCR analysis of mRNA changes in VEGF, PPARγ, HIF-1α, PGC-1α, COX4, AK3, LDH, PFK, PKm and SOD-2. No significant differences between the HT and NC were detected by independent-samples t-test with Bonferroni correction for multiple comparisons (P>0.05) in relative changes of mRNA abundance. There were no significant differences between groups for heart rate and blood lactate during the treadmill test. The outcomes indicated that this hypoxia training program did not cause a significant variation in basal level expression of the selected mRNAs in Thoroughbreds as compared with normoxic training.

Four weeks of high‐intensity training in moderate, but not mild hypoxia improves performance and running economy more than normoxic training in horses

“…In equine studies, whereas (Davie et al, 2017) reported no additional improvements in heart rate and blood lactate concentration during incremental treadmill tests after 6 weeks of moderate‐intensity hypoxic training (3 hypoxic and 3 normoxic sessions/week, total 30 min/session, 15% inspired O 2 ), Ohmura et al (2017) demonstrated that all‐out running for 2–3 min in hypoxia (15.1% inspired O 2 ) twice a week for 3 weeks increased of well‐trained horses in normoxia. Our previous study in horses also showed that 4 weeks of high‐intensity training in hypoxia (100% 2 min, 3 sessions/week, 15% inspired O 2 ) improved performance, , and maximal cardiac output to a greater extent than normoxic training (Mukai et al, 2020).…”

“…Previously, we reported that high‐intensity training (100% for 3 min, 3 sessions/week for 4 weeks) in moderate hypoxia (15% O 2 ) improves run time and at incremental exercise tests (IET) in normoxia to a greater extent than the same training in normoxia (Mukai et al, 2020), which indicates that hypoxic training may be a strong strategy for better exercise performance without increasing absolute training speed and/or distance. However, very few studies have examined hypoxic training in horses (Davie et al, 2017; Ohmura et al, 2017), and further studies are needed to determine the optimal severity of hypoxia and the intensity, duration, and volume of training in hypoxia.…”

High‐intensity training in normobaric hypoxia enhances exercise performance and aerobic capacity in Thoroughbred horses: A randomized crossover study

“…While Davie et al . (2017) failed to show any changes in heart rate and blood lactate concentration during a treadmill test after 6 weeks of moderate‐intensity training under hypoxic conditions (15% inspired O 2 ) in horses, whereas, our another study has demonstrated that all‐out running for 2–3 min in hypoxia (15.1% inspired O 2 ) twice a week for 3 weeks increased O 2 max (+8.9%) of well‐trained horses in which O 2 max had not increased over 3 consecutive weeks of supramaximal training in normoxia (Ohmura et al., 2017). These results suggest that exercise mode and intensity are also likely key factors for horses in mediating the response to the LLTH program, with higher training intensities appearing to be more beneficial than submaximal workloads as McLean et al .…”

“…Therefore, there are arguments that an increase in the number of circulating erythrocytes and hemoglobin caused by altitude training may not result in an additional benefit in aerobic capacity and exercise performance because maximal cardiac output may decline due to the increased blood viscosity above the optimal hematocrit (Boning, Maassen, & Pries, 2011). However, very few reports exist on the effects of altitude/hypoxic training in horses (Davie et al., 2017; Ohmura, Mukai, Takahashi, Takahashi, & Jones, 2017).…”

Epigenetic control of exercise adaptations in the equine athlete: Current evidence and future directions

“…There has been a small number of equine studies 91‐95 that examined the haematological changes and performance in horses in response to altitude training. However, limited studies have investigated the underpinning genetic and molecular mechanisms in horses training in hypoxia 96‐99 …”