Abstract

INTRODUCTION

It is well known that high intensity exercise causes an increase in reactive oxygen species (ROS), altering the redox balance and increasing oxidative stress [1, 2]. This increase in ROS can cause damage to the cell membrane and dysfunctions in the cellular mitochondria [3], which are associated with increased fatigue and loss of performance [4, 5].

Many athletes ingest buffer substances to increase the antioxidant response and improve the performance of aerobic and anaerobic metabolism. The hydrogen acts as an efficient antioxidant by rapid diffusion into living tissues and cells [6, 7]. Most antioxidant supplements are limited in their cellular distributions, but hydrogen has the ability to effectively penetrate biomembranes and infiltrate into the mitochondria and the nucleus [8, 9]. Hydrogen can be administered by different methods (inhalation of H₂ gas or injectable saline solution) but the easiest and safest way is the intake of hydrogen-rich water (HRW), without adding a colour change or water flavour [10]. Recently, some studies have concluded that molecular hydrogen might have healthy effects on the body, inducing antioxidant and anti-inflammatory responses, and limiting the metabolic acidosis [11–13]. HRW supplementation has been shown to have a positive effect on repeated-sprint ability performance, muscle fatigue and ventilatory response [14–17]. Similarly, the inhalation of 4% gaseous hydrogen during a week improved the peak running velocity of physically active men and women [18].

Currently there are different devices on the market that produce HRW, and even bags/bottles of different sizes that contain supposedly hydrogenated water are sold. The electrolysis technology used to enrich the water determines the pH level, the hydrogen concentration and the oxidation-reduction potential (ORP), decisively influencing these factors in terms of the ability to eliminate ROS. Another determining factor to promote the absorption of hydrogen by the cell membrane is the size of the hydrogen bubble. In the same vein, it has been suggested that the antioxidant activity of nano-bubble HRW (≤ 717 ± 387-nm diameter) is superior to normal hydrogen water containing a similar or lower level of dissolved hydrogen but not nano-bubbles [19].

On the other hand, the antioxidant response against the attack of ROS is more effective in trained individuals than in non-trained individuals, since they have a greater antioxidant capacity and a better immune response to exercise [17, 20]. These training-induced adaptations could also influence the ergogenic effect of HRW intake. To the best of our knowledge, there is only one previous study [17] that has tried to analyse the positive effect of HRW intake taking into account the athlete performance level, although it was conducted with a small sample size and with an acute intake that was only performed for 24 hours.

Therefore, the main aim of the study was to analyze the ergogenic effect of 7-day intake of nano-bubble HRW on aerobic and anaerobic performance, both in trained amateur cyclists and in untrained subjects. We hypothesized that the intake of HRW may be beneficial for athletes, reducing fatigue and increasing the aerobic and anaerobic performance.

MATERIALS AND METHODS

RESULTS

All participants completed the study and no person reported any adverse effects that could be related to HRW intake.

Table 1 shows the results obtained in the incremental VO₂max test by both amateur trained cyclists and untrained subjects. The trained cyclists achieved significantly higher values of VO₂max, VT2 %VO₂max, Wmax and TTE in both the PW and HW protocol. An interaction effect (p = .043) on the lactate concentration was observed in trained cyclists after the intake of HRW, although with a small effect size (d = .33). No significant effect was observed in untrained subjects.

Table 2 shows the results obtained in the maximum anaerobic test by participants. The trained cyclists had better values of PP, MP and FI in both PW and HW protocols. It was observed that HRW had an interaction effect with the Training factor, observing a moderate positive effect on PP (d = .51), MP (d = .51) and FI (d = 0.45) in trained cyclists. However, HRW compared with PW did not have a clear effect in untrained subjects.

DISCUSSION

The findings of the study show that HRW intake for one week had a positive effect on the performance (PP, MP and FI) of trained cyclists during the anaerobic test, but no significant effect on untrained exhaustion; RPE: Rated perceived exertion. subjects. Previous studies have shown that the antioxidant capacity of the organism can be influenced by the status training [20, 29], so the magnitude of the effect of the HRW could also be influenced by this variable.

Recently Botek, Krejčí [17] concluded that the ergogenic effect of acute HRW intake on performance in a 4.2-km up-hill race is determined by the athlete performance level, noting that performance improved in the 4 slowest athletes, and remained without significant improvement in the 4 fastest athletes. This result is totally contrary to those obtained in our study, in which we observed that the intake of HRW only had an ergogenic effect in the trained subjects (with a VO₂max greater than 60 ml/min*kg). It is difficult to contrast the results between the two studies because the protocol used and the HRW were very different. In the aforementioned study, an acute intake of HRW was carried out for a short period of 24 hours before the race (in the present research, a 7-day intake was used), and most decisively, a bottled HRW without nano- or micro-bubbles with an H₂ concentration of only 0.9 ppm was used (in our study, HRW nano-bubbles with a concentration of 1.9 ppm were used). In this vein, the effectiveness of hydrogenated water will depend on the type of HRW used, the way of administration and the duration of the intervention.

The performance improvement in trained cyclists after HRW ingestion occurred with a moderate magnitude of the effect during the anaerobic test, achieving an increase in PP and MP, and a decrease in FI. However, no aerobic improvement was observed in the incremental VO₂ test, except for a lower lactate concentration after HRW. These results are similar to those observed in a previous study in which the PP did not decrease during a repeated sprint protocol after using HRW for 2 weeks, but it did after control water intake [15]. Aoki, Nakao [14], although with a different protocol in footballers on an isokinetic machine, also observed that the decrease in peak torque and blood lactate level were lower during the HRW protocol. The alteration of the redox balance, as well as the accumulation of metabolites and H⁺ that are produced in the muscle fibre during intense exercise, cause a decrease in the contractile capacity of the muscle and a loss of performance [4, 30]. Although the molecular mechanisms involved in the efficacy of HRW have to be further investigated, ingesting this type of water seems to have an anti-fatigue effect, suppressing the reduction in biological antioxidant potential, increasing lactate dehydrogenase and glutathione peroxidase activity, and scavenging cytotoxic ROS [7, 19, 31]. Apart from the direct neutralization of ROS, hydrogen appears to activate the endogenous anti-oxidative system by nuclear factor erythroid-2-related factor 2 (Nrf2) system and its haem oxygenase-1 (HO-1) [32]. Additionally, H₂ could alter mitochondrial energy metabolism and hormone secretion [33]. In this sense, it has been observed that HRW intake caused up-regulation of ghrelin, a peptide hormone that increases appetite, stimulates the release of growth hormone and helps to maintain lean mass [34], factors that could improve performance during exercise. Even improvements in mood and autonomic nerve function have also been observed after taking HRW for 4 weeks [35].

Therefore, unlike what happened in untrained subjects, the higher antioxidant and metabolic capacity of trained cyclists, added to the intake of HRW, caused a synergistic effect that allowed them to develop a greater and more lasting effort in anaerobic conditions, reaching higher power levels and lower FI. However, the effects of long-term HRW intake on performance should be specifically evaluated since a decrease in serum ferritin (iron storage/transporter protein in the body) has been observed after inhaling molecular hydrogen for one week [18]. Furthermore, the circulating ghrelin concentration (its levels increase with HRW intake) has been associated with increased body fat [36].

The study had some limitations. Blood samples were not taken to analyse oxidative stress parameters, making it difficult to assess the antioxidant effect of HRW. Methodologically, there was no washout period between the two phases of water supplementation. The HRW was performed only during a period of 7 days; thus it would not be possible to extrapolate these findings to long-term intervention, since alternative or even opposite results could be observed. According to the hormesis theory, an excessive dose of HRW could reverse the positive effects observed with this short-term intervention.

CONCLUSIONS

The beneficial effects of HRW are mediated by the training status of athletes. Seven-day intake of nano-bubble HRW improved anaerobic performance of trained cyclists, but had no effect on untrained subjects. Therefore, the HRW intake seems to be an effective hydration strategy, although a greater number of studies are necessary to define precisely the duration of intake, the amount of water and the most effective concentration of hydrogen to individually optimize the ergogenic effects of HRW.

Acknowledgment

REFERENCES