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

Abstract

We examined the effects of high-intensity training in normobaric hypoxia on aerobic capacity and exercise performance in horses and the individual response to normoxic and hypoxic training. Eight untrained horses were studied in a randomized, crossover design after training in hypoxia (HYP; 15.0% inspired O 2 ) or normoxia (NOR; 20.9% inspired O 2 ) 3 days/week for 4 weeks separated by a 4-month washout period. Before

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

“…Consistent with human studies (Roels et al, 2005; Truijens et al, 2003) and our previous study (Mukai et al, 2020), hemoglobin concentrations both at rest and at exhaustion in all groups did not increase after training in our present study. While LHTH and/or LHTL training usually aims to enhance athletic performance by stimulating an increase in serum erythropoietin and erythrocyte volume, only a few well‐controlled LLTH studies on trained or elite athletes have reported increments in hemoglobin concentration (Bonetti et al, 2006), and none have reported any increases in erythrocyte volume and/or hemoglobin mass.…”

“…, , and SV max at IET increased similarly in all groups throughout the study. In our previous study (Mukai et al, 2020), however, we observed greater , , and SV max in the hypoxic group compared to that of the normoxic group in a similar study design. The causes for these differences are not clear, but the minor differences in the training intensity (100% vs. 95% ), the degree of hypoxia (15% O 2 vs. 16% or 18% O 2 ), and the age of horses (6.5 years vs. 7.9 years) might affect training adaptation on aerobic capacity.…”

“…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). Training programs varied among these studies, including intensity and duration of training, training status of horses (untrained or trained), and hypoxic exposure duration, but these interventions used similar O 2 concentrations of hypoxic gas.…”

“…Therefore, improvements in both aerobic and anaerobic capacity are needed to enhance equine racing performance. 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.…”

Moderate‐intensity training in hypoxia improves exercise performance and glycolytic capacity of skeletal muscle in horses

“…There was no significant difference in run time between NOR and HYP and the increase in run time in HYP was relatively smaller in this study compared to our previous results of high-intensity hypoxic training despite the same/ similar F I O 2 and the same training duration and frequency being used (Mukai et al, 2020(Mukai et al, , 2021. The smaller improvements in performance may be due to the lower training intensity compared to our previous studies, as McLean et al (McLean et al, 2014) stated that improvements in exercise performance at sea level appear most likely after high-intensity and short-term training in hypoxia.…”