Abstract

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Introduction

Since energy demands and oxygen consumption increase during supermaximal exercise, such as intermittent running, sprints, and jumps, production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) also increase, threatening to disturb redox balance and cause oxidative stress. During normal conditions, ROS and RNS are generated at a low rate and subsequently eliminated by the antioxidant systems. However, a greatly increased rate of ROS production may exceed the capacity of the cellular defense system. Consequently, substantial free radicals’ attack on cell membranes may lead to a loss of cell viability and to cell necrosis and could initiate the skeletal muscle damage and inflammation caused by exhaustive exercise [1–3]. Although well-trained athletes suffer from less oxidative stress reduction because their antioxidant systems adapt, accumulation of intense exercise can provoke an increase in oxidative stress [4]. To mitigate oxidative stress-induced adverse events during sports, antioxidant supplementation among athletes has been well documented. Although results of these studies are often contradictory depending on the antioxidant compounds and quantity, some studies demonstrate the beneficial effects of antioxidants on muscle fatigue or performance [5,6].

Recently, the beneficial effects of hydrogen-rich water (HW) have been described in experimental and clinical disease conditions [7,8]. Although research on the health benefits of HW is limited and there is scant data on long-term effects, pilot studies on humans suggest that consuming HW may help prevent metabolic syndrome [9], diabetes mellitus [10], and cancer patients’ side effects with radiotherapy [11]. Since hydrogen is known to scavenge toxic ROS [12] and induce a number of antioxidant proteins [13,14], we hypothesized that drinking HW may be beneficial for athletes in reducing oxidative stress-induced muscle fatigue following acute exercise. In this study, we evaluated the efficacy of hydrogen-rich water on healthy subjects by measuring muscle fatigue and blood lactate levels after exercise. Although further studies are needed to elucidate the exact mechanisms and benefits, this report suggests that hydrogen-rich water might be an appropriate hydration fluid for athletes.

Methods

Results

Blood analysis for lactic acid, d-ROMs, BAP and CK

As shown in Table , blood d-ROMs BAP and CK levels increased after exercise in subjects in both groups treated with PW and HW. However, there was no statistical difference between the groups. Eventhough the blood lactate level were significantly increased in both HW and PW at 45 and 60 min after exercise, these levels were comparably and significantly lower in the HW than in the PW group (Figure ).

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Table 2

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		0 min	45 min	60 min	90 min	120 min
d-ROMs (U.CARR)	PW	269.0 ± 50.8	285.7 ± 52.3*	287.0 ± 56.9*	274.2 ± 50.2	280.0 ± 47.6
	HW	281.3 ± 61.8	303.5 ± 46.3*	308.6 ± 56.1*	296.1 ± 57.9	307.0 ± 45.8
BAP (μmol/L)	PW	2347.3 ± 155.8	2648.9 ± 96.5*	2632.8 ± 146.4*	2349.6 ± 152.0	2321.8 ± 196.9
	HW	2336.7 ± 123.1	2659.1 ± 102.1*	2664.6 ± 201.0*	2299.8 ± 104.6	2356.4 ± 143.7
CK (IU/L)	PW	247.0 ± 105.1	296.5 ± 119.9*	300.9 ± 127.7*	264.7 ± 113.3*	256.3 ± 111.7
	HW	407.4 ± 269.9	483.2 ± 314.0*	478.1 ± 314.5*	428.2 ± 282.0	353.7 ± 264.6

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Sequential changes of blood lactate levels during exercise. Blood lactate levels in the athletes given PW significantly increased immediately after exercise compared to the levels at pre-exercise. HW significantly reduced blood lactate levels post exercise using bicycle ergometer. (*p < 0.05 vs. time 0. #p < 0.05 vs HW, N = 10).

Maximal knee extension exercise

At analysis for maximal knee extension exercise, we divided into five frames of 100-repetition knee extension at the peak torque of isokinetic knee extension exercise [18]. Each frame was corresponded to 20 repetitions; Frame 1 for the first 20 repetitions, Frame 2 for the following 21-40 repetitions, Frame 3 for 41-60 repetitions, Frame 4 for 61-80 repetitions and Frame 5 for the last 81-100 repetitions. Although the peak torque of subjects treated with PW significantly decreased during the first 40 repetitions (Frame 1-2), the reduction of peak torque in the subjects given HW did not reach statistical difference, suggesting that HW inhibited the early decrease of peak torque of the subjects (Figure A).

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(A) Changes in peak torque (PT) every 20 repetitions (rep = 1 frame) during 100 maximum isokinetic knee extensions. PT of the subjects treated with PW significantly decreased during the initial 40-60 contractions by approximately 20-25 % of the initial values, followed by a phase with little change. On the other hand, there was no statistical difference between Frame 1 and Frame 2 in HW, indicating that HW prevented the decreasing the peak torque during the first 2 Frames. HW, Hydrogen rich water; PW, Placebo water. (*p < 0.05 vs Frame 1, N = 10). (B) Changes in median frequency (MDF) every 20 repetitions (rep = 1 Frame) during 100 maximum isokinetic knee extensions. Although exercise significantly reduced MDF values during the first 2 Frames, there was no statistical difference between HW and PW in all Frames. HW, Hydrogen rich water; PW, Placebo water. (*p < 0.05 vs Frame 1, N = 10). (C) Changes in mean power frequency (MPF) every 20 repetitions (rep = 1 Frame) during 100 maximum isokinetic knee extensions. There was no statistical difference between HW and PW in all Frames. HW, Hydrogen rich water; PW, Placebo water. (*p < 0.05 vs Frame 1, N = 10).

Discussion

In this preliminary study, we showed that hydration with HW attenuated increase of blood lactate levels and prevented post-exercise decrease of peak torque, an indicator of muscle fatigue. Muscle fatigue is caused by many different mechanisms, including the accumulation of metabolites within muscle fibers and the generation of an inadequate motor command in the motor cortex. The accumulations of potassium, lactate, and H⁺ have often been suggested as being responsible for the decrease in muscle contractility [19]. In addition, aerobic, anaerobic, or mixed exercise causes enhanced ROS production, resulting in inflammation and cellular damage [20]. Short bursts of heavy exercise may induce oxidative stress through various pathways such as electron leakage within mitochondria, auto-oxidation of the catecholamine, NADPH activity, or ischemia/reperfusion [21]. Although the mechanism involved in the efficacies of HW remains unclear, our results show that hydration with HW could be feasible for acute exercise. Proper and adequate hydration is helpful for elite athletes to achieve the best performance. HW can easily replace regular drinking water on a routine basis and would potentially prevent adverse effects associated with heavy exercise.

Factors such as age, nutritional status, training level, and physical activity category can influence the results [22,23]. Although we had anticipated that hydrogen, a known antioxidant, would reduce oxidative stress following acute exercise, the effects of oral intake of HW were marginal and did not affect the level of oxidative markers after exercise. This can be explained by the facts that the athletes in our study have routinely trained and their antioxidant defense systems may be more active. Previous studies reported that repeated aerobic training increases antioxidant enzyme activity and subsequently decreases oxidative stress [2,24–26]. Also, considering the short life-span of hydrogen in circulation [27], more frequent drinking of HW during exercise might have additional effects. In a future study, the efficacy of HW on untrained subjects or recreational exercisers, who may have poorly established antioxidant systems to combat exercise-induced oxidative stress, should be tested. Furthermore, different drinking protocols should be investigated.

We quantified muscle fatigue as a decline in the maximal force or power capacity of muscle, which means that submaximal contractions can be sustained after the onset of muscle fatigue. Similarly, blood lactate concentration is one of the most often measured parameters during clinical exercise testing, as well as during performance testing of athletes. Lactate has often been considered one of the major causes of both fatigue during exercise and post-exercise muscle soreness. Lactate generated from the anaerobic breakdown of glycogen in the muscle occurs only during short bouts of relatively high intensity exercise and it is usually related to fatigue and muscle soreness. Previous evidence has shown that inorganic phosphate from creatine phosphate was the main cause of muscle fatigue [28].

Dehydration in athletes may also lead to fatigue, poor performance, decreased coordination, and muscle cramping. Although further investigations will be warranted, drinking HW may be an appropriate hydration strategy [29]. In this study, we administered HW or PW to subjects prior to exercise. Further investigation is required to determine the best timing, dose, and hydrogen concentration of drinking water to optimize the effects of HW.

In conclusion, our preliminary data demonstrated that consumption of HW reduced blood lactate levels and improved muscle fatigue after acute exercise. Although further studies are absolutely warranted, drinking HW would be a novel and effective fluid hydration strategy for athletes.

Competing interests

The authors declare that they have no competing interests.

Authors’ contributions

KA, TA and YM participated in the protocol design and the data accumulation. AN conceived the study and drafted the manuscript. SM participated in the study design and coordination. All authors read and approved the final manuscript.

References