Abstract

INTRODUCTION

Ergogenic supplements are popular among athletes who are hoping to enhance athletic performance, reduce fatigue, improve recovery, and prevent exercise-induced harm from reactive oxygen/nitrogen species (ROS/RNS) and excessive inflammation [1,2]. Antioxidants and anti-inflammatories are often consumed by athletes to prevent the harmful effects of ROS/RNS, and inflammation; however, many of the benefits of exercise may be mediated by the exercise-induced production of ROS and inflammation [3].

Some studies have demonstrated that supplementation with conventional antioxidants results in deleterious effects that can negate the benefits of exercise training (e.g., mitochondrial biogenesis) [4]. A likely explanation could be that exogenous antioxidants are not effective at maintaining redox homeostasis, but may instead exacerbate redox dysregulation [5].

Hydrogen gas (H₂), which can easily permeate bio-membranes and subcellular compartments [6], may have ergogenic properties due to its anti-inflammatory and anti-oxidant-like effects [7]. Although H₂ has antioxidant-like effects and is considered a reducing agent in organic chemistry, it is too stable to react with important signaling oxidants (e.g., ^•O₂⁻, NO^•, H₂O₂) [6,8]. This mitigates the risk of hampering exercise training benefits. Hydrogen appears to act via hormesis in which it activates the Nrf2 pathway and subsequent induction of phase 2 antioxidant enzymes [9]. Additionally, H₂ modulates signal transduction, protein phosphorylation cascades, and gene expression. These influences can favorably modulate inflammatory pathways (NFAT, NF-κB, TLRs) [10–12], increase PGC-1α (marker of mitochondrial biogenesis) [13,14], maintain mitochondrial membrane potential and ATP production [14,15], increase resilience to stress [16], and influence other signaling molecules (e.g., Nrf2, Nox1,STAT3, etc.) [11].

Results from clinical studies suggest inhalation of hydrogen gas or ingestion of hydrogen-rich water (HRW) may benefit individuals who have experienced or are experiencing cerebral infarction [17], post-cardiac arrest syndrome [18], rheumatoid arthritis [19], mild cognitive impairments [20], Parkinson’s disease [21], metabolic syndrome [22,23], mitochondrial myopathies [24] and other diseases previously reviewed [7]. The effect of HRW on measurements of exercise performance, recovery, and tolerance to submaximal and maximal exercise in healthy and diseased populations is less well documented. However, these studies suggest that HRW may prevent early fatigue and reduce lactate levels [25,26], improve range of motion and recovery from soft tissue injury [27], attenuate delayed onset muscle soreness from eccentric exercise [28], prevent exercise-induced decline in antioxidant enzymes [28], and improve the ability to maintain peak power output during repetitive sprints [29]. Most of these athletic studies examined the effect of chronic supplementation (H₂ administration for over 24 hours). Therefore, the purpose this double-blind repeated measures study was to investigate the effects of acute hydrogen supplementation, compared to placebo, on indices of submaximal and maximal aerobic exercise performance as measured by VO₂, respiratory exchange ratio (RER), heart rate (HR), and respiratory rate (RR) in a young, non-diseased population.

MATERIALS AND METHODS

RESULTS

The influence of molecular hydrogen on various exercise performance indices was evaluated during a graded treadmill exercise test to exhaustion. Data was collected for 19 subjects (15 males and 4 females) who underwent all three trials. The data of one subject was mistakenly not recorded and re-testing did not occur. Minimum and maximum values of HR, VO₂, RER and RR were not significantly different across conditions (p > 0.05) (Table 3).

In contrast, analysis of mean HR from start of exercise (i.e. 1 min) to end of exercise revealed that there was a significant decrease in the average HR for HRW compared to both the baseline (≈3 bpm ± 0.4, p < 0.001) and the placebo (≈4 bpm ± 0.4, p < 0.001) (see Table 4). Placebo slightly increased HR (≈1 bpm ± 0.4) compared to baseline (p < 0.05). Compared to placebo, HRW had a slightly higher VO₂ (p < 0.05), but was no different compared to baseline (p > 0.05). Placebo lowered VO₂ compared to baseline (p < 0.05). However, the absolute value of the effect was small (≈1 mL *kg⁻¹ * min⁻¹

Pairwise differences in estimated marginal means with Bonferroni correction were also conducted at 1–9 minutes of exercise (see Table 5). On average, compared to baseline and placebo, HRW gave a lower HR (p < 0.001) by 3.6 bpm and 5.1 bpm (p < 0.001), respectively. HRW also significantly lowered the average RR compared to placebo (p = 0.018). However, compared to baseline, VO₂ and RER were not changed by HRW (p > 0.05), while compared to placebo they were higher (p < 0.001) and lower (p < 0.001), respectively. However, in placebo, VO₂ and RER were lower and higher, respectively compared to baseline (p < 0.001). The magnitude or effect size of these differences on all variables are rather small (Cohen’s d < 0.14). The mean HR and corresponding 95% confidence intervals for each group for the 1–9 minute subsample are presented in Fig. 1. Table 6 shows the similar calculated statistics with Bonferroni correction from 9.5 minutes until the end of exercise. Similar to measurements at 1–9 min and of the entire sample, HRW showed a slightly lower heart rate compared to baseline (p = 0.022) and placebo (p = 0.001). Compared to baseline, HRW did not influence VO₂ (p > 0.05), but it was higher compared to placebo (p < 0.05), and placebo was lower than baseline (p < 0.05). RER, compared to baseline was slightly higher with HRW (p = 0.021), but not different compared to placebo (p > 0.05). RER was higher in placebo compared to baseline (p < 0.05). There was no statistically significant differences in RR in any of the groups.

DISCUSSION

The effects of HRW on the exercise performance indices of HR, VO₂, RER, and RR were evaluated during a maximal exercise treadmill test using a double-blinded, placebo-controlled cross-over study.

There were no significant differences in either HR, VO₂, RR, or RER between trials at maximal or minimal exercise intensities. This suggests, HRW does not increase maximal HR, RR, VO₂, or RER in young healthy adults. Several previous studies have shown that H₂ improves submaximal exercise performance including reduction in fatigue and lactate levels [25,31]. We therefore analyzed the entire exercise trial and specific time intervals in order to determine the influence of HRW at various exercise intensities. Analysis of the entire sample revealed that HRW decreased the average exercising HR and RR and the effect on HR was especially pronounced at submaximal exercise intensities.

On average HRW decreased exercising HR by several beats per min while maintaining the same VO₂ level compared to placebo. The Fick equation illustrates that VO₂ = (stroke volume × HR) × (a-v) O₂ difference. If HRW decreases exercise HR and VO₂ is simultaneously maintained then we can speculate that HRW improves stroke volume and/or improves oxygen extraction and utilization at the muscle cell. It is unknown if H₂ has such an effect. However, several exercise studies have shown that H₂ decreases lactate levels [25,31]. Lactate production occurs when the ATP derived from mitochondrial oxidative phosphorylation cannot maintain the cellular energy demands. This requires oxidation of cytosolic NADH in order to produce ATP from glycolytic substrate-level phosphorylation. NAD⁺ is replenished by the reduction of pyruvate when forming lactate. Therefore, H₂ may decrease lactate concentration by improving mitochondrial function, which would correspondingly increase oxygen extraction. However, maximal levels of VO₂, HR, and RER were not significantly different, which suggests, in this population, HRW may only be effective at submaximal exercise intensities. More research is needed to confirm this observation and elucidate the molecular mechanisms.

Greater practical differences may have been evident if equal percentages of submaximal exercise had been compared. Additionally, instead of using time as the independent variable, using percentage of time, or percentage of maximal VO₂ or HR as the independent variable may be more useful. For example, in our study, total exercise time was different for each participant due to varying levels of fitness and any specific minute mark corresponded to different percentages (e.g., 9 min corresponds to around 60% to 90%) of total exercise time depending on the participant. Instead of comparing the exercise indices at the same time interval future research should compare each value as a function of a specific exercise intensity (e.g., 70%) for each participant. This was not feasible in our study due to the problem of discreetness of measurement. Since these values were recorded every 30 seconds instead of more frequent sampling. Although prediction of the values by mathematical interpolation (y = mx + b) is possible, the differential between the 30 second intervals had substantial variability and linear interpolation would have been too inaccurate. Furthermore, the amount of time spent at a given intensity (e.g., 70%), was significantly different for each individual since the time to exhaustion during the graded-treadmill max test ranged from 10 to 15 minutes.

Future research should examine the effect of HRW on HR, VO₂, RR, RER, and time to exhaustion at specific exercise intensities. Similarly, a range of distances could also be selected (e.g., 5 km or 10 km), and time trials could be performed with or without HRW. Future research should also determine the effect of HRW on rating of perceived exertion and blood lactate concentrations at various exercise intensities.

Our study was limited by a relatively small sample size and few female participants. The positive or the null effects of HRW may be different in older, younger, or diseased populations. Additionally, participants’ diet/calories and daily exercise patterns were not controlled or recorded nor was exact time of consumption of DrinkHRW or placebo capsules. Participants were asked to take the capsules the night before the test and at least approximately 30 min prior to the test. Perhaps the effects of HRW are altered if consumed in close conjunction with food since intestinal bacteria produce high levels of H₂ upon metabolism of non-digestible carbohydrates [32]. The statistically significant benefits observed in this study and associated with HRW supplementation have unknown practical applications in regards to aerobic exercise performance and tolerance. The Cohen’s d of these changes suggest a small effect size; however, a better designed study may show greater practical significance to athletes. Additionally, small changes may become substantial under some scenarios (e.g., lower HR during marathon, elite athletic competitions, etc.).

CONCLUSION

Our results suggest that acute supplementation with molecular hydrogen does not improve maximal exercise performance in young healthy adults; however, it significantly reduces exercising HR at submaximal intensities. Although more studies are needed to determine the impact of HRW in diseased and non-diseased populations, the high safety profile of HRW coupled with this and previous studies, suggest that HRW could be a viable option as an ergogenic aid for athletes seeking to improve aerobic exercise performance.

ACKNOWLEDGEMENTS

REFERENCES