Women’s fitness has begun to acquire a different vocabulary. The familiar emphasis on burning calories, losing weight, and staying slim has not disappeared, but it increasingly shares space with conversations about lifting weights, building muscle, becoming stronger, and remaining physically capable with age. A recent review of the history of resistance training in women describes a long period in which cultural norms and stereotypes discouraged women from strength training, followed by growing acceptance of muscular strength as part of women’s health and athletic performance. Popular health culture has moved in a similar direction, with the phrase “strong is the new skinny” capturing a broader shift from exercise pursued primarily for slenderness toward strength, function, and healthy aging.
However, the growing visibility of women’s fitness has not necessarily translated into equally widespread participation. In combined 2022 and 2024 survey data representing more than 56 million U.S. women aged 18–44 years, only 25.1% reported enough leisure-time activity to meet recommendations for both aerobic and muscle-strengthening exercise, while 47.2% met neither recommendation. The gap was particularly large for strength training: 55.3% reported doing no muscle-strengthening activity at all. Across U.S. adults more broadly, 42.4% of women met the federal aerobic-activity recommendation in 2024, compared with 52.3% of men.
Those numbers take on greater meaning when fitness is separated from appearance. Muscle strength can be trained throughout adulthood, and a 2026 systematic review and meta-analysis of 126 studies involving 4,019 women found substantial improvements in muscular strength after resistance training in both premenopausal and postmenopausal women, together with increases in functional mass and reductions in fat mass. Resistance training in women has also been associated with improvements in strength, power, bone health, metabolic health, cardiovascular function, and other measures that extend well beyond changes in body size.
Fitness, in that sense, is not simply the amount of exercise completed. It is the capacity that repeated exercise leaves behind. Each exercise session creates a temporary physiological challenge, and skeletal muscle responds to mechanical loading, changing energy demand, calcium movement, metabolites, hormones, and other signals by altering the molecular processes that regulate its structure and function. When those challenges are repeated, the accumulated responses can remodel muscle in ways that alter its size, force production, endurance, and contractile properties. Aerobic and resistance exercise produce different patterns of adaptation, but both depend on the ability of tissues to sense a demand and change in response to it.
That adaptation also depends on what happens after the workout. Unaccustomed or demanding exercise can temporarily reduce muscle function and produce soreness, structural disruption, and inflammatory responses, while tightly regulated inflammation also participates in subsequent muscle repair and adaptation. Recovery therefore requires more than simply eliminating the stress produced by exercise. Muscle has to restore function and control excessive damage while retaining the signals that help it adapt to the work it has just performed.
Molecular hydrogen (H₂) has begun to be studied within that recovery response. H₂ is a small gas that diffuses readily through biological tissues and can be administered through inhalation or water containing dissolved hydrogen. Biomedical studies have examined its effects on oxidative stress as well as redox-sensitive and inflammatory signaling, making exercise particularly relevant because some of the same pathways can participate in both tissue stress and adaptation. Experimental exercise research also suggests that H₂ can reduce some markers of oxidative stress without suppressing several of the mitochondrial signals activated by training, meaning that it should not be thought of as a traditional antioxidant, which can blunt all redox signals.
In humans, the research findings are particular notable when recovery is measured after demanding exercise. In a randomized, double-blind crossover study of 12 elite finswimmers, eight of whom were women, hydrogen-rich water was associated with lower creatine kinase activity, less muscle soreness, and slightly greater countermovement-jump height 12 hours after two strenuous training sessions performed on the same day. A longer trial examined H₂ specifically in women. Twenty-two elite female handball and skeleton athletes were randomized to hydrogen-rich water or placebo water for 28 days. Hydrogen-rich water was associated with greater maximal torque, lower creatine kinase, increased muscle-mass percentage, and reduced fat-mass percentage, although perceived stress and recovery did not significantly improve.
The same biology may matter outside competitive sport. In a 2025 randomized pilot trial, 27 previously untrained adults over age 50, including 18 women, completed six weeks of resistance training while consuming either hydrogen-rich water or control water. Muscle performance improved in both groups, while hydrogen-rich water produced greater reductions in biomarkers of acute exercise-induced muscle damage. The participants became stronger through training, while H₂ appeared to influence part of the physiological response occurring around that training.
Physical capacity also depends on what happens before and during exercise: muscle has to obtain and use fuel as demand changes. Skeletal muscle is a major site of glucose and lipid metabolism, and the ability to shift fuel use in response to changing conditions is part of the metabolic flexibility that supports both exercise and metabolic health.
Two small studies in women suggest that H₂ may reach this side of fitness biology as well. In a randomized, double-blind crossover study of 20 healthy, physically active young women, 60 minutes of H₂ inhalation at rest reduced respiratory exchange ratio, consistent with greater reliance on fat oxidation during the intervention. Furthermore, in ten overweight middle-aged women, four weeks of an H₂-generating intervention did not significantly change body weight, BMI, or body circumference compared with placebo, but it produced greater reductions in body-fat percentage and arm-fat index, lower triglycerides, and a more favorable fasting-insulin response.
National Women’s Health and Fitness Day is therefore a useful reminder that fitness is not simply something measured by body weight, calories burned, or athletic performance. It is physical capacity built over time: the strength to produce force, the metabolic flexibility to meet changing demands, and the ability to recover well enough for repeated exercise to produce adaptation rather than simply fatigue. That capacity matters whether the goal is competing in sport, becoming stronger for the first time, or preserving the ability to keep moving and training later in life.
The emerging H₂ research fits within that larger process rather than outside it. In women and female-dominant study populations, H₂ supplementation has been associated with changes in muscle damage, soreness, recovery of function, body composition, substrate use, and metabolic regulation. While exercise provides the mechanical and metabolic stimulus that builds strength and endurance, H₂ may influence how effectively the body manages some of the stress, repair, and metabolic work required to turn that stimulus into lasting physical capacity.
Seen that way, the shift from “skinny” toward “strong” reaches deeper than a change in fitness culture. It places the emphasis on what a woman’s body can continue to do, how well it can adapt when challenged, and how much of that capacity can be carried forward into the years ahead.
References
· Chaoqun, L., Yuqi, Z., Shi, Z., Zhenghui, Y., & Li, W. (2021). A Comparison of the Antioxidant Effects Between Hydrogen Gas Inhalation and Vitamin C Supplementation in Response to a 60-Min Treadmill Exercise in Rat Gastrocnemius Muscle. Frontiers in physiology, 12, 745194. https://doi.org/10.3389/fphys.2021.745194
· Conklin, K. K., Nakayama, J. Y., Van Dyke, M. E., Harley, K. G., & Thompson, H. R. (2025). Leisure-time physical activity among women of reproductive age—United States, 2022 and 2024. Morbidity and Mortality Weekly Report, 74(41), 634–639. https://doi.org/10.15585/mmwr.mm7441a2
· Egan, B., & Sharples, A. P. (2023). Molecular responses to acute exercise and their relevance for adaptations in skeletal muscle to exercise training. Physiological reviews, 103(3), 2057–2170. https://doi.org/10.1152/physrev.00054.2021
· Egan, B., & Zierath, J. R. (2013). Exercise metabolism and the molecular regulation of skeletal muscle adaptation. Cell metabolism, 17(2), 162–184. https://doi.org/10.1016/j.cmet.2012.12.012
· Elgaddal, N., & Kramarow, E. A. (2026). Aerobic physical activity among adults age 18 and older: United States, 2024. NCHS Data Brief, 555, 1–13. https://doi.org/10.15620/cdc/174653
· Goodpaster, B. H., & Sparks, L. M. (2017). Metabolic Flexibility in Health and Disease. Cell metabolism, 25(5), 1027–1036. https://doi.org/10.1016/j.cmet.2017.04.015
· Grepl, P., Botek, M., Krejčí, J., & McKune, A. (2025). Molecular hydrogen inhalation modulates resting metabolism in healthy females: findings from a randomized, double-blind, placebo-controlled crossover study. Medical gas research, 15(3), 367–373. https://doi.org/10.4103/mgr.MEDGASRES-D-24-00085
· Isenmann, E., Geisler, S., Havers, T., Siegert, F., Hemke, F., & Held, S. (2026). It's never too late: The impact of resistance training on strength and body composition in females across the lifespan - A systematic review and meta-analysis. Journal of science and medicine in sport, 29(10), 1174–1185. https://doi.org/10.1016/j.jsams.2026.03.002
· Korovljev, D., Trivic, T., Drid, P., & Ostojic, S. M. (2018). Molecular hydrogen affects body composition, metabolic profiles, and mitochondrial function in middle-aged overweight women. Irish journal of medical science, 187(1), 85–89. https://doi.org/10.1007/s11845-017-1638-4
· Kraemer, W. J., Fragala, M. S., & Ratamess, N. A. (2025). Evolution of resistance training in women: History and mechanisms for health and performance. Sports medicine and health science, 7(5), 351–365. https://doi.org/10.1016/j.smhs.2025.01.005
· Kuzmanovic, J., Todorovic, N., Ranisavljev, M., Javorac, D., Korovljev, D., Tarnava, A., Stajer, V., & Ostojic, S. M. (2025). The effects of drinking hydrogen-rich water for six weeks on exercise-related biomarkers in exercise-naïve men and women over 50 years following resistance training program: a randomized controlled pilot trial. Research in sports medicine (Print), 33(6), 711–721. https://doi.org/10.1080/15438627.2025.2521474
· Ogannisyan, M., Slivin, A., LeBaron, T. W., Tarnava, A., Karmazin, V., Bazanovich, S., Dolgachev, V., Vychik, A., Strizhkov, A., & Parastaev, S. (2025). Hydrogen-Rich Water Decreases Muscle Damage and Improves Power Endurance in Elite Athletes: A Randomized, Double-Blinded, Placebo-Controlled Trial. Journal of lifestyle medicine, 15(1), 8–17. https://doi.org/10.15280/jlm.2025.15.1.8
· Ohta S. (2014). Molecular hydrogen as a preventive and therapeutic medical gas: initiation, development and potential of hydrogen medicine. Pharmacology & therapeutics, 144(1), 1–11. https://doi.org/10.1016/j.pharmthera.2014.04.006
· Peake, J. M., Neubauer, O., Della Gatta, P. A., & Nosaka, K. (2017). Muscle damage and inflammation during recovery from exercise. Journal of applied physiology (Bethesda, Md. : 1985), 122(3), 559–570. https://doi.org/10.1152/japplphysiol.00971.2016
· Salamon, M. (2026, January 22). Strong is the new skinny. Harvard Health Publishing. https://www.health.harvard.edu/womens-health/strong-is-the-new-skinny
· Sládečková, B., Botek, M., Krejčí, J., Valenta, M., McKune, A., Neuls, F., & Klimešová, I. (2024). Hydrogen-rich water supplementation promotes muscle recovery after two strenuous training sessions performed on the same day in elite fin swimmers: randomized, double-blind, placebo-controlled, crossover trial. Frontiers in physiology, 15, 1321160. https://doi.org/10.3389/fphys.2024.1321160
