Effect of practical hyperoxic high-intensity interval training on exercise performance
Introduction
All-out high-intensity interval training (HIIT), which normally consists of four to seven 30-s maximal efforts with 4- or 4.5-min recovery, has been shown to effectively improve exercise performance despite shorter training time. A previous study reported that all-out HIIT increased cycling endurance capacity as well as peak power output during the Wingate test (Burgomaster et al., 2005). In addition, all-out HIIT can result in the same degree of improvement in maximal oxygen uptake (VO2max) and time trial performance as traditional continuous endurance training despite a much shorter total training time (Burgomaster et al., 2008; Cocks et al., 2013; Shepherd et al., 2013). Moreover, similar improvements in buffering capacity (Gibala et al., 2006), glycogen content (Gibala et al., 2006), oxidative capacity (Burgomaster et al., 2008), and microvascular density (Cocks et al., 2013), in working muscle are also elicited following all-out HIIT and endurance training. These findings suggest that all-out HIIT is an effective and time-efficient regimen to induce favorable muscle adaptation and improvement of exercise performance.
Quite recently, inhalation of hyperoxic gas has been reported to affect the all-out HIIT-induced performance adaptation. Our research group demonstrated that a short-term 3-week all-out HIIT program (four to six 30-s all-out cycling with 4-min passive recovery, 2 times per week) under systemic hyperoxia improved the blood lactate curve during submaximal incremental exercise, but not under normoxia (Kon et al., 2019). This result suggests that all-out HIIT under hyperoxia may be useful for improvement of aerobic capacity in active skeletal muscle. Hyperoxia exposure increased the contribution of the aerobic energy system during maximal exercise (Linossier et al., 2000). Therefore, the increased stimulus to the aerobic metabolic system may contribute to the improvement of aerobic capacity in skeletal muscle by all-out HIIT under hyperoxia. However, this all-out model of HIIT may not be suitable for the general population as it requires a high motivation and can cause severe fatigue and discomfort (e.g. nausea) due to excessive physical effort (Coyle, 2005; Little et al., 2010). Moreover, a HIIT model that has a longer exercise time at a constant lower intensity may be more effective in stimulating the aerobic metabolic system than an all-out model of HIIT. Thus, the development of a more practical model of HIIT, with a longer exercise time at a constant lower intensity, under hyperoxia may be required.
Until now, several previous studies have investigated the effect of submaximal HIIT under systemic hyperoxia on exercise performance. However, the results have been inconsistent (Kilding et al., 2012; Perry et al., 2005, 2007). In addition, the total exercise time (including recovery time between intervals) of these HIIT models was long (≥60 min). The strong point of the HIIT is the ability to improve exercise performance even if the exercise time is short. Additionally, because many adults do not engage in habitual exercise due to a lack of time (Shepherd et al., 2013), the time efficiency of HIIT should be maintained.
This study investigated the effect of a more practical model of HIIT under hyperoxia on aerobic and anaerobic exercise capacity in trained athletes. We hypothesized that a more practical model of HIIT under hyperoxia would be effective for improving aerobic capacity, such as the blood lactate curve, during submaximal exercise.
Section snippets
Subjects
Sixteen healthy male college athletes belonging to a canoe club at the same university participated in this study. They engaged in canoe-specific training 5 days per week. Characteristics of the participants are shown in Table 1. All subjects were non-smokers and not taking any medications. They were randomized to 2 groups: normoxic HIIT (NHIIT, n = 8) group or hyperoxic HIIT (HHIIT, n = 8) group in a single-blind manner. The experimental procedure was approved by the Japan Institute of Sports
Training time and volume
Training time increased gradually in both the NHIIT and HHIIT groups (NHIIT: 1 st week 658 ± 79 s, 2nd week 855 ± 86 s, 3rd week 891 ± 80 s; HHIIT: 1 st week 720 ± 87 s, 2nd week 896 ± 57 s, 3rd week 995 ± 58 s; main effect, P < 0.01). Training volume also tended to increase progressively in both groups (NHIIT: 1st week 272 ± 21 kJ, 2nd week 290 ± 22 kJ, 3rd week 305 ± 24 kJ; HHIIT: 1st week 311 ± 27 kJ, 2nd week 320 ± 22 kJ, 3rd week 356 ± 23 kJ; main effect, P = 0.07). However, no significant
Discussion
In this study, we demonstrated that the blood lactate curve during submaximal intermittent exercise and mean power output during the 90-s maximal exercise increased significantly only in the HHIIT group. In addition, the total exercise time (including rest intervals) of the HIIT model in this study was short (< 20 min). These results suggest that the HHIIT model used in this study may be time-efficient and effective for improving aerobic capacity (blood lactate curve) and anaerobic performance
Author contributions
Design and conduct of the study, acquisition of subjects and data, analysis and interpretation of data, and preparation of manuscript: MK and KN. Acquisition of data, and analysis and interpretation of data: YE.
Declaration of Competing Interest
The authors declare they have no conflicts of interest.
Acknowledgements
This work was supported by JSPS KAKENHI [grant nos. 11J09235 and 22700644].
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These authors contributed equally to this work.