Alleviation of exercise-induced injury by hydrogen inhalation via the reduction of oxidative stress and inflammation in athletes

Abstract

Background

Strenuous exercise can lead to exercise-induced lung injury, primarily driven by elevated oxidative stress and systemic inflammation. Although hydrogen (H₂) inhalation has been proposed as a nonpharmacological intervention with antioxidant and anti-inflammatory potential, its effects in the context of exercise remain poorly understood. This study aimed to investigate whether H₂ inhalation could mitigate exercise-induced systemic stress responses in athletes.

Methods

Thirty-one healthy athletes were divided into a control group (n=14), an infrared blanket group (n=9), and a H₂ inhalation group (n=8). Blood samples were collected before and after winter training to evaluate oxidative stress [total antioxidant capacity (T-AOC), superoxide dismutase (SOD), and malondialdehyde (MDA)], inflammation and lung injury-related markers [white blood cell count (WBC)], C-reactive protein (CRP), hematological indicators [red blood cell count (RBC), hemoglobin (HB), hematocrit (HCT), and mean corpuscular volume (MCV)], biochemical indicators [creatine kinase (CK) and blood urea nitrogen (BUN)], and stress-related hormones [total cholesterol (T), cholesterol (C), and ferritin (FE)]. Lung injury was considered to reflect exercise-induced lung stress. The systemic and inflammatory indices of stimulation were inferred.

Results

After a single postexercise intervention, the H₂ group showed improved antioxidant capacity and reduced WBC and CRP levels. These effects persisted after winter training. Moreover, the H₂ group maintained stable RBC, HB, and HCT levels, unlike the infrared blanket group, suggesting better preservation of oxygen-carrying capacity and hematological stability.

Conclusions

H₂ inhalation attenuates exercise-induced lung injury by reducing oxidative stress and inflammation. It may represent a promising adjunctive approach for protecting pulmonary function during intensive athletic training in the winter.

Highlight box.

Key findings

• A single session of hydrogen (H₂) inhalation administered after acute exercise, prior to the winter training period, alleviated exercise-induced oxidative stress and systemic inflammation in athletes.

• Compared with the control and infrared blanket groups, the H₂ group maintained more stable red blood cell parameters and antioxidant capacity following winter training.

What is known and what is new?

• Intense physical activity induces oxidative damage and inflammation, contributing to exercise-related lung injury.

• This study indicated that H₂ inhalation offers protective effects against pulmonary injury by modulating systemic oxidative and inflammatory responses.

What is the implication, and what should change now?

• H₂ therapy may serve as a novel, noninvasive strategy to reduce lung damage in high-performance athletes and should be considered in future recovery protocols.

Introduction

Intense exercise enhances adaptability through metabolic activation but also triggers oxidative stress and inflammation, which are major concerns in sports medicine (1). During exercise, a surge in skeletal muscle oxygen consumption leads to excessive production of reactive oxygen species (ROS), which can induce oxidative stress when it exceeds the clearance capacity of the antioxidant system (2). This metabolic imbalance activates inflammatory signaling pathways such as nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κb), promotes the release of proinflammatory factors, and thus recruits neutrophils and macrophages (3). The resulting inflammation not only impairs gas exchange but also disrupts the alveolar-capillary barrier, leading to exercise-induced bronchoconstriction, pulmonary edema, and, in chronic cases, pulmonary fibrosis (4,5). Over time, such inflammatory responses can cause diffuse lung injury, which is characterized by alveolar structural disruption, interstitial edema, increased airway permeability, and ultimately the development of exercise-induced lung injury (6). It is worth noting that repeated intense exercise may trigger a maladaptive cycle, in which unresolved oxidative stress and persistent low-grade inflammation impair the resilience of the lungs, especially in untrained individuals or those with pre-existing respiratory diseases. In addition, long-term overtraining may also lead to immune system disorders, heart enlargement, and other problems (7). Therefore, identifying effective strategies to mitigate exercise-induced oxidative stress and inflammatory lung responses may be highly beneficial. In addition to post-exercise interventions, pre-exercise preventive strategy also plays a crucial role. For example, hydration has been shown to reduce exercise-induced bronchoconstriction and preserve pulmonary function (8).

Existing strategies for postexercise recovery mainly focus on relieving muscle fatigue and promoting metabolic waste removal (9). Among them, infrared therapy is widely used due to its ability to improve local blood circulation, reduce muscle soreness, and accelerate recovery (10), usually through devices such as infrared blankets (11). Infrared therapy promotes vasodilation and tissue metabolism by emitting infrared radiation that penetrates the surface tissue (12). However, the therapeutic effect of infrared blankets is mainly limited to superficial tissues, and its ability to regulate oxidative stress and inflammatory responses in the deep lungs remains poorly understood. Exercise-induced lung injury involves alveolar epithelial damage, oxidative imbalance, and persistent inflammation at the microvascular level, but infrared therapy has limited efficacy in preventing or alleviating such injuries. Therefore, more targeted interventions are needed to address systemic oxidative stress and inflammation to provide better protection for lung function after intense exercise.

In recent years, hydrogen (H₂) has attracted increased attention as a part of a novel therapeutic approach due to its unique antioxidant and anti-inflammatory properties. As a small, nonpolar molecule, H₂ can quickly penetrate biological membranes and selectively scavenge hydroxyl radicals (OH) and peroxynitrite (ONOO⁻) without interfering with normal redox signals (13). In addition, H₂ can inhibit the activation of NF-κB and NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasomes, thereby reducing the release of proinflammatory factors and alleviating tissue inflammation (14). An increasing number of studies have shown that H₂ therapy has a protective effect against various diseases associated with oxidative stress and inflammation. Notably, H₂ inhalation has demonstrated efficacy in alleviating the lung injury caused by ischemia-reperfusion and sepsis. A previous study confirmed that H₂ relieves lung oxidative stress and inflammatory response by regulating the ferroptosis and glutathione metabolic pathways and could alleviate acute lung injury in a cecum ligation and puncture mouse model (15). One study found that H₂ treatment promoted macrophage polarization to the M2 subtype in a mouse radiation lung injury model by inhibiting the NF-κB signaling pathway, thereby alleviating the inflammatory response (16). Another study demonstrated that H₂ inhalation can effectively alleviate lipopolysaccharide (LPS)-induced acute lung injury, primarily by activating the AMP-activated protein kinase (AMPK) signaling pathway (17). This leads to the suppression of inflammatory mediators and downregulation of apoptosis-related proteins such as Drp1 and Caspase-3, thereby improving lung function, reducing inflammation and edema in lung tissue, and enhancing survival rates. However, the potential role of H₂ in preventing or alleviating exercise-induced lung injury remains underexplored.

Given the limitations of conventional physical therapies in mitigating oxidative stress and lung inflammation, this study aimed to evaluate the protective effects of H₂ inhalation against exercise-induced lung injury by determining its ability to reduce oxidative and inflammatory responses following intense exercise. Additionally, we compared its efficacy with that of infrared therapy to elucidate the relative effectiveness of these two interventions and to explore more effective strategies for lung protection and recovery in athletes undergoing intensive training. We present this article in accordance with the TREND reporting checklist (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-1278/rc).

Methods

Participants

Initially, this study recruited 46 healthy volunteers from Shanghai No.2 Sports School, aged 15–27 years old, who had been engaged in long-term training in athletics, cycling, weightlifting, and other sports; swimming was not among the included sports. All participants had received regular professional training for a minimum of 3 years, with the majority engaged in 5 years or more of continuous practice in their respective sports. The cohort consisted of both male and female athletes. Sex distribution across the groups is detailed in Table 1. All participants underwent a health assessment before the group was formed to confirm that they had no cardiovascular disease, respiratory disease, metabolic disorder, or other serious underlying diseases. Because some participants did not complete the exercise test or intervention procedures, the final sample size for analysis consisted of 31 individuals. The study was conducted between November 2024 and April 2025. All exercise tests, interventions, and biochemical analyses were performed at the Shanghai Minhang District Central Hospital and the medical clinic of the Shanghai No.2 Sports School. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. This study was approved by the Ethics Committee of Shanghai Minhang District Central Hospital (approval No. 2025-approval-005-015). Written informed consent was obtained from all participants or their legal guardians before enrollment.

Table 1. Baseline characteristics of participants before winter training vs. after winter training.

ID	Gender	Age (years)	Before winter training				After winter training
			Health status	Pre-existing conditions	Treatment		Health status	Pre-existing conditions	Treatment
MH13	Male	27	Good	No	Hydrogen		Healthy	No	Hydrogen
MH15	Male	22	Healthy	No	Hydrogen		Healthy	No	Hydrogen
MH16	Male	20	Healthy	No	Hydrogen		–	–	–
MH17	Female	20	Healthy	No	Hydrogen		–	–	–
MH18	Male	20	Healthy	No	Hydrogen		Healthy	No	Hydrogen
MH20	Female	17	Healthy	No	Hydrogen		Healthy	No	Hydrogen
MH21	Male	19	Healthy	No	Hydrogen		Healthy	No	Hydrogen
MH22	Male	18	Healthy	No	Hydrogen		Healthy	No	Hydrogen
MH24	Female	21	Healthy	No	Infrared blanket		Healthy	No	Infrared blanket
MH25	Male	20	Good	No	Infrared blanket		Healthy	No	Infrared blanket
MH26	Male	24	Good	No	Infrared blanket		Healthy	No	Infrared blanket
MH27	Female	20	Healthy	No	Infrared blanket		Healthy	No	Infrared blanket
MH28	Male	21	Healthy	No	Infrared blanket		–	–	–
MH29	Male	22	Healthy	No	Infrared blanket		–	–	–
MH30	Male	20	Healthy	No	Infrared blanket		–	–	–
MH31	Female	18	Healthy	No	Infrared blanket		Healthy	No	Infrared blanket
MH32	Male	17	Healthy	No	Infrared blanket		–	–	–
MH33	Male	18	Healthy	No	Control		–	–	–
MH34	Male	17	Healthy	No	Control		–	–	–
MH35	Male	16	Good	No	Control		Healthy	No	Control
MH36	Male	18	Healthy	No	Control		Healthy	No	Control
MH37	Male	15	Healthy	No	Control		Healthy	No	Control
MH38	Male	15	Good	No	Control		Healthy	No	Control
MH39	Male	15	Healthy	No	Control		Healthy	No	Control
MH40	Female	16	Healthy	No	Control		Good	No	Control
MH41	Male	16	Healthy	No	Control		Healthy	No	Control
MH42	Female	16	Good	No	Control		Good	No	Control
MH43	Male	16	Healthy	No	Control		Healthy	No	Control
MH44	Male	16	Good	No	Control		–	–	–
MH45	Male	15	Healthy	No	Control		Healthy	No	Control
MH46	Male	16	Healthy	No	Control		Healthy	No	Control

Study design and intervention protocol

This study adopted a nonrandomized controlled intervention design. A total of 31 healthy volunteers were included. They first completed a standardized exercise test, including two rounds of repeated short-distance sprint cycling training, with each round consisting of 10 seconds of maximum power sprint (load set to 7.5% of body weight) and 110 seconds of unloaded low-speed cycling (60 rpm) (Figure 1A). After the exercise test, the participants were divided into three groups according to the principle of voluntariness and training schedule and received the following interventions: (I) the control group (n=14) recovered naturally after exercise, inhaling room air. (II) The infrared blanket group (n=9) received intervention with a infrared thermal therapy device (infrared blanket) after exercise for 20 minutes. (III) The H₂ group (n=8) received H₂ inhalation intervention performed immediately after exercise. The mixed gas was generated using a H₂ gas generator (AMS-H-03, Asclepius Meditec, Shanghai, China). The inhaled gas components were 66.7% H₂, 33.3% O₂, 0% CO₂, and balanced N₂, and the gas flow was set to 3 L/min for 20 minutes. During the intervention, all participants first rested in a sitting position for 10 minutes, then completed 20 minutes of moderate-intensity cycling at 60% peak oxygen uptake (VO₂peak), and finally had a 5-minute recovery period (Figure 1B). Given the nature of the interventions, participants were aware of their group allocation, and no blinding was applied during the intervention phase.

Figure 1.

Study design and intervention protocols. (A) Flowchart illustrating the recruitment and group allocation of 31 participants. All participants underwent a standardized repeated sprint cycling exercise (10 s at 7.5% BW + 110 s at 60 rpm, repeated twice), followed by intervention, including control (n=14), infrared blanket (n=9), or hydrogen inhalation (n=8). (B) Experimental timeline showing the procedure for the hydrogen and control trials, including 10-min seated rest (room air), 20-min cycling exercise at 60% VO₂peak, and 5-min recovery. During the trial, the hydrogen group inhaled 66.7% H₂ and 33.3% O₂, 0% CO₂, and balanced N₂, while the control group inhaled 21% O₂, 0% CO₂, and balanced N₂. BW, body weight; VO₂peak, peak oxygen uptake.

Postwinter training evaluation

After the initial intervention, all 31 participants continued their regular winter training regimen. After winter training, 24 of the original 31 participants agreed to participate in follow-up testing and were reassigned to the same groups based on their original intervention: H₂ (n=6), infrared blanket (n=9), and control (n=9).

Blood sample collection

Fasting blood samples were collected from the antecubital vein of each participant 7 hours prior to the first exercise session (day 1) and 16 hours after completion of the exercise tests on day 2, day 3, and day 4. Samples were centrifuged at 3,000 rpm for 15 minutes at 4 ℃, and the serum was separated and stored at −80 ℃ for subsequent biochemical analyses.

Biochemical analysis

Serum levels of oxidative stress and inflammation-related biomarkers were measured with standardized methods. The levels of total antioxidant capacity (T-AOC), superoxide dismutase (SOD), malondialdehyde (MDA), testosterone (T), cortisol, ferritin (FE), and C-reactive protein (CRP) were determined with commercial enzyme-linked immunosorbent assay (ELISA) kits (Nanjing Jiancheng Bioengineering Institute, Nanjing, China) following the manufacturer’s instructions. Hematological parameters, including white blood cell count (WBC), red blood cell count (RBC), hemoglobin (HB), hematocrit (HCT), and mean corpuscular volume (MCV), were analyzed with an automated hematology analyzer (XE-2100, Sysmex Corporation, Kobe, Japan). Creatine kinase (CK) and blood urea nitrogen (BUN) levels were determined with enzymatic colorimetric assays on a fully automated biochemical analyzer (Hitachi 7600, Tokyo, Japan). All measurements were performed in accordance with standard laboratory procedures and quality control practices.

Statistical analysis

Statistical analyses and figure generation were performed using GraphPad Prism 9.0 (Dotmatics, Boston, MA, USA). All data are presented as mean ± standard deviation (SD). Due to the small and exploratory sample size of this study, a formal statistical normality test was not performed; however, a histogram was used to visually assess the data distribution, indicating approximate normality. One-way analysis of variance (ANOVA) was used to compare differences between the three groups (control, infrared blanket, and H₂) within each time point and was followed by the Tukey multiple comparison test. A P value less than 0.05 was considered statistically significant.

Results

Baseline characteristics of participants

A total of 31 healthy athletes (aged 15–27 years) voluntarily participated in this study and completed the prewinter training assessments. Based on their training plans and willingness, they were assigned into three groups: control (n=14), infrared blanket (n=9), and H₂ inhalation (n=8). The baseline characteristics, including age, gender, and health condition, are summarized in Table 1.

Effects of intervention before winter training

Oxidative stress biomarkers

As shown in Figure 2A-2C, participants in both the infrared blanket and H₂ groups demonstrated significantly enhanced antioxidant capacity, reflected by elevated levels of T-AOC and SOD, as compared to the control group. In contrast, the level of MDA, a marker of lipid peroxidation, was significantly reduced in the intervention groups. Among the groups, the H₂ group exhibited the most pronounced improvement, suggesting a stronger capacity of H₂ to alleviate exercise-induced oxidative stress.

Figure 2.

Effects of hydrogen inhalation and infrared blanket intervention on oxidative stress biomarkers before winter training. (A) T-AOC, (B) SOD, and (C) MDA levels were measured in all three groups before winter training. Both intervention groups (infrared blanket and hydrogen) showed significantly increased T-AOC and SOD levels compared to control, with the hydrogen group showing the most pronounced effect. The MDA levels were significantly reduced in both intervention groups, especially in the hydrogen group. *, P<0.05 versus control group. MDA, malondialdehyde; SOD, superoxide dismutase; T-AOC, total antioxidant capacity.

Inflammatory and tissue injury indicators

As shown in Figure 3, the WBC in the infrared blanket group and the H₂ group was slightly lower than that in the control group (Figure 3A), indicating that systemic inflammation was reduced after the intervention. The RBC, HB, and HCT levels of each group remained relatively stable (Figure 3B-3D), indicating that the intervention did not affect the overall blood homeostasis. The MCV of both intervention groups decreased significantly. The T (Figure 3F) and FE (Figure 3H) levels in the H₂ group were significantly higher than those in the control group, indicating that the acute endocrine stress response was enhanced after strenuous exercise. The cortisol (Figure 3G) level in the infrared blanket group was significantly lower than that in the control group, and the cortisol level in the H₂ group was slightly lower than that in the control group, but the difference was not statistically significant. In terms of biochemical damage markers, there was no significant difference in BUN levels between the groups (Figure 3I). The CK level in the H₂ group was significantly increased, indicating a stronger muscle response (Figure 3J). Although not statistically significant, the CRP level in the H₂ group was the lowest, suggesting a possible anti-inflammatory effect (Figure 3K). Overall, these results suggest that H₂ inhalation can have beneficial effects on systemic inflammation and neuroendocrine stress even before winter training begins.

Figure 3.

Changes in systemic inflammation, hematological parameters, endocrine indicators, and biochemical markers before winter training. (A-E) WBC, RBC, HB, HCT, and MCV were measured to assess the systemic inflammation and hematological status. (F-H) T, C, and FE were quantified as endocrine indicators. (I-K) BUN, CK, and CRP were used to assess muscle damage and inflammation. Significant improvements in T and FE were observed in the hydrogen group, while CK levels were notably elevated, suggesting a pronounced post-exercise stress response. *, P<0.05 versus control group. BUN, blood urea nitrogen; C, cortisol; CK, creatine kinase; CRP, C-reactive protein; FE, ferritin; HB, hemoglobin; HCT, hematocrit; MCV, mean corpuscular volume; RBC, red blood cell count; T, testosterone; WBC, white blood cell count.

Effects of intervention after winter training

A total of 24 participants completed follow-up assessments after winter training, and their characteristics are detailed in Table 1. All three groups retained comparable distributions in terms of age and gender.

Oxidative stress markers posttraining

As presented in Figure 4A-4C, the T-AOC and SOD levels remained elevated in both infrared blanket and H₂ groups, while MDA levels continued to decline. This pattern was consistent with the pretraining findings, indicating the sustained antioxidant effect of both interventions. In terms of enhancing antioxidant defense, the H₂ group performed consistently better than did the infrared blanket group.

Figure 4.

Posttraining changes in oxidative stress biomarkers among the three groups. (A) T-AOC, (B) SOD, and (C) MDA levels were measured after winter training. Both hydrogen and infrared blanket groups showed significantly increased T-AOC and SOD levels and decreased MDA levels as compared to the control group, indicating sustained antioxidant effects. *, P<0.05 versus control group. MDA, malondialdehyde; SOD, superoxide dismutase; T-AOC, total antioxidant capacity.

Systemic inflammation and physiological indices

As shown in Figure 5A, both the infrared blanket and H₂ groups exhibited significantly reduced WBC counts as compared to the control group, suggesting the alleviation of exercise-induced systemic inflammation. Regarding hematological markers (Figure 5B-5E), the infrared blanket group showed notable reductions in red RBC, HB, HCT, and MCV levels as compared to controls, while the H₂ group maintained relatively stable values in RBC, HB, and HCT but also showed a significant decrease in MCV. As shown in Figure 5F-5H, the T, cortisol, and FE levels were elevated in both intervention groups as compared with the control group. The median values in the H₂ group were consistently higher than those in the infrared blanket group, indicating a more pronounced neuroendocrine response after exercise. Both infrared blanket and H₂ groups showed significantly lower BUN (Figure 5I) and CK (Figure 5J) levels compared to the control group. However, the H₂ group exhibited a statistically significant increase CRP (Figure 5K) levels posttraining, whereas no significant change was observed in the infrared group. Taken together, these results suggest that while both interventions helped reduce the markers of inflammation and tissue damage, the stress hormone response was greater in the H₂ inhalation group, suggesting complex physiological adaptations to prolonged training.

Figure 5.

Posttraining comparisons of inflammatory, hematological, and physiological indicators. (A) WBC, (B) RBC, (C) HB, and (D) HCT represent systemic inflammation and hematological status. (E) MCV, (F) T, (G) C, and (H) FE reflect neuroendocrine and iron storage responses. (I) BUN, (J) CK, and (K) CRP serve as indicators of muscle stress, renal function, and inflammation. The hydrogen and infrared blanket groups showed diverse modulations across these markers, with the hydrogen group generally maintaining hematological homeostasis and exhibiting enhanced stress and recovery responses. *, P<0.05 versus control group. BUN, blood urea nitrogen; C, cortisol; CK, creatine kinase; CRP, C-reactive protein; FE, ferritin; HB, hemoglobin; HCT, hematocrit; MCV, mean corpuscular volume; RBC, red blood cell count; T, testosterone; WBC, white blood cell count.

Discussion

This study assessed the protective effects of H₂ inhalation and infrared thermotherapy blanket therapy on exercise-induced lung injury in athletes, focusing on oxidative stress, systemic inflammation, and hematological homeostasis. The results suggest that oxidative stress may play a central role in a variety of lung injury mechanisms. One study reported that oxidative stress induces ferroptosis and autophagy by destroying the structure and function of mitochondria, thereby inducing lung epithelial cell damage (18). In lung injury caused by nanoplastic exposure, oxidative stress is a key mediating mechanism and is accompanied by hepcidin degradation, iron ion release, and alveolar-capillary barrier dysfunction. Another study found that long-term cigarette smoke exposure significantly reduced T-AOC in rat lung tissue and weakened the clearance of ROS, thereby aggravating lung injury through oxidative damage and impaired DNA repair mechanisms (19). This suggests that decreased T-AOC levels play a key role in lung injury caused by cigarette smoke. Based on this observation, further investigation is warranted to clarify how H₂ regulates T-AOC levels. Understanding this mechanism may help elucidate its protective role against oxidative stress and lung injury. Our results suggest that H₂ inhalation can provide more potent and more sustained antioxidant and anti-inflammatory effects than can infrared heat therapy, both before and after winter training. Before winter training, participants who received H₂ inhalation had significantly increased levels of T-AOC and SOD, which was accompanied by decreased levels of MDA, indicating enhanced resistance to oxidative stress.

Inflammation is another important contributor to exercise-induced lung injury (20). Studies have shown that excessive inflammation can damage the lung epithelium, destroy the alveolar-capillary barrier, and cause immune cell infiltration (21,22). In clinical and exercise settings, CRP and WBC are commonly used inflammatory markers and have important clinical value in inflammatory-related diseases (23). CRP levels can rise rapidly in the early stage of inflammation, reflecting the intensity of systemic inflammatory response, and are not easily disturbed by hormones or other elements, suggesting its suitability for the dynamic monitoring of changes in lung inflammation (24). WBC and its differential counts (such as that of neutrophils) can help determine the type and severity of inflammation, especially in cases of bacterial pneumonia (25). In this study, inhalation of H₂ continued to reduce WBC levels before and after winter training, and CRP levels before training were also suppressed. These results suggest that H₂ may reduce exercise-induced systemic inflammation by regulating immune responses. The CRP levels in the H₂ group increased after training, which could be related to the adaptive stress response rather than persistent inflammation.

Cortisol is a typical stress hormone in the body. Its abundance often increases significantly during strenuous exercise or inflammatory response, and it contributes to the regulation of metabolic, immune, and inflammatory processes (26). Studies have shown that excessive secretion of cortisol can aggravate lung inflammation, damage the alveolar-epithelial barrier, and promote the oxidative stress response (27,28). In this study, cortisol was significantly suppressed in the infrared blanket group, while it was only slightly increased in the H₂ group, suggesting that the two interventions may regulate stress states through different neuroendocrine pathways. It is worth noting that a previous study have proposed that cortisol can be regulated through neuroendocrine mechanisms such as the hypothalamic-pituitary-adrenal (HPA) axis to reduce tissue stress and inflammatory damage and exert a protective effect against exercise-induced lung injury (29); however, direct evidence linking cortisol to the intervention measures used in this study is still limited, and thus further research is necessary.

In addition to oxidative stress and inflammation, other physiological and hematological parameters were also affected by the intervention measures. Hematological indicators such as RBC, HB, and HCT in the H₂ group remained relatively stable after training, suggesting that these individuals were able to maintain good oxygen-carrying capacity and blood rheology during high-intensity exercise. Studies have shown that intense exercise can reduce the stability of red blood cell membranes and impair HB function, thereby affecting the efficiency of oxygen transport (30,31). H₂ may maintain membrane integrity through antioxidant effects and alleviate this adverse effect (32). In addition, the decrease in MCV observed in the two intervention groups may reflect the accelerated regeneration and morphological changes of red blood cells caused by training, which is a common adaptive response to the miniaturization of athletic red blood cells.

In terms of hormone metabolism, the increase in T and FE levels after training, especially in the H₂ group, was more significant, indicating enhanced anabolic capacity and improved iron storage capacity. Previous studies have found that iron metabolism disorder is one of the key mechanisms of exercise-induced lung injury (33,34). Excessive free iron can promote the Fenton reaction to produce hydroxyl free radicals, aggravating oxidative damage (35). FE, as an iron ion buffer, may exert a protective effect. H₂ may participate in the maintenance of iron homeostasis in lung tissue by regulating FE expression. This effect could help reduce oxidative and inflammatory synergistic damage. A previous experiment demonstrated that H₂ can reduce the expression of muscle damage markers and reduce exercise-induced renal tubular oxidative stress by regulating the AMPK and mTOR signaling pathways (36). In addition, in our study, the levels of CK and BUN in the H₂ group after training were lower, indicating that H₂ inhalation can effectively relieve skeletal muscle stress and protein decomposition load after intense exercise.

In this study, the H₂ inhalation protocol involved a gas mixture composed of 1% H₂, 21% O₂, 0% CO₂, and 78% N₂, closely resembling the composition of ambient air. While H₂ was the active therapeutic agent under investigation, the safety profile of the accompanying gases also warrants brief discussion. N₂ is considered biologically inert under normobaric conditions, and adverse effects such as inflammatory responses are primarily observed in extreme contexts such as hyperbaric environments or rapid decompression, which do not apply to this study. Similarly, the oxygen concentration used was identical to that of room air and did not pose an added oxidative burden. Therefore, under the controlled normoxic and normobaric conditions applied here, the inhaled gas mixture is considered physiologically safe, and it is unlikely that either N₂ or O₂ confounded the observed antioxidant and anti-inflammatory effects of H₂.

Furthermore, although this study included both male and female athletes, sex-specific analyses were not performed. A study showed that estrogen, the predominant female sex hormone, possesses antioxidant and anti-inflammatory properties that may modulate exercise-induced oxidative stress and systemic inflammation (37). These hormonal influences could contribute to differing physiological responses to H₂ inhalation between sexes. For example, estrogen has been reported to attenuate ROS production and suppress proinflammatory cytokine release, potentially conferring greater resilience to oxidative damage in females. Therefore, the absence of stratified analysis by sex represents a limitation of this study, and future research should consider sex hormones and menstrual cycle phases to delineate sex-based differences in recovery outcomes better. In addition, the participants in this study were exclusively engaged in land-based sports such as athletics, cycling, and weightlifting. Aquatic sports, including swimming, were not represented. Given that training in water imposes distinct physiological demands—such as altered pulmonary mechanics due to hydrostatic pressure, breath-hold patterns, and temperature regulation—exercise-induced oxidative stress and recovery responses may differ significantly between aquatic and land-based athletes (38). As such, the generalizability of our findings to athletes in water-based disciplines remains uncertain and warrants further exploration in future studies.

The results of this study revealed the buffering and regulatory capacity of H₂ intervention on multisystem loads induced by intense exercise from multiple levels of hematological and metabolic responses, providing theoretical support the potential of H₂ application in sports rehabilitation and lung disease intervention. However, this study involved certain limitations that should be addressed. First, the sample size was relatively small, which may limit the statistical power of the findings. Second, the experimental period was short, and the long-term dynamic observation of the sustained effect of H₂ intervention during training adaptation was not possible. In addition, this study mainly observed the changes in systemic indicators and lacked direct evidence at the lung function or tissue level. In the future, respiratory mechanics parameters or lung imaging can be combined to further verify the direct protective effect of H₂ against exercise-related lung injury. Finally, investigations at the mechanism level remained insufficient, and subsequent molecular pathway research can be applied to further identify the key molecular targets involved in H₂-mediated regulation of oxidative stress, iron metabolism, and immune response.

Conclusions

H₂ inhalation therapy was found to alleviate exercise-induced lung injury by reducing oxidative stress and systemic inflammation while helping to maintain hematological stability. Compared with infrared blanket therapy, H₂ inhalation showed relatively greater potential in supporting antioxidant defenses, attenuating inflammatory responses, and preserving RBC function and oxygen transport capacity during and after high-intensity winter training. These findings suggest that H₂ inhalation may serve as a promising and safe adjunctive strategy to support recovery and mitigate pulmonary stress during strenuous physical activity or athletic training. Further studies with larger sample sizes and long-term follow-up are warranted to confirm these preliminary observations and elucidate the underlying mechanisms.

Supplementary

The article’s supplementary files as

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. This study was approved by the Ethics Committee of Shanghai Minhang District Central Hospital (approval No. 2025-approval-005-015). Written informed consent was obtained from all participants or their legal guardians before enrollment.

Data Sharing Statement

Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-1278/dss

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DOI: 10.21037/jtd-2025-1278