Menopause represents a critical stage in a woman’s life, during which ovarian function gradually declines, leading to a significant reduction in circulating estrogen levels (McCarthy and Raval, 2020) and triggering a series of physiological deteriorations. Among these, the decline in skeletal muscle mass and function is particularly prominent, manifesting as muscle atrophy, reduced strength, and impaired physical performance (Pellegrino et al., 2022; Lu and Tian, 2023). These changes not only significantly impair the quality of life in postmenopausal women but also markedly increase the risks of falls, fractures, and other health complications (Barron et al., 2020). Epidemiological evidence highlights the clinical significance of sarcopenia in postmenopausal women. A cross-sectional study of 340 Thai women aged 45–65 reported a prevalence of 11.8% for pre-sarcopenia and 2.7% for sarcopenia (Orprayoon et al., 2021). In another large-scale investigation of elderly postmenopausal women not receiving hormone replacement therapy, the prevalence of sarcopenia was found to be as high as 22.6% (Kenny et al., 2003). Consequently, how to effectively mitigate estrogen deficiency-induced muscle loss has garnered widespread attention and become a major research focus in exercise physiology and health sciences.

As one of the key regulators of host health, the gut microbiota interacts closely with host metabolism and immune systems and plays a critical role in the regulation of skeletal muscle mass and function (Lahiri et al., 2019; Zhang T. et al., 2022). According to the “gut–muscle axis” hypothesis, gut microbes may influence muscle metabolic homeostasis through microbial metabolites (e.g., short-chain fatty acids) (Frampton et al., 2020), inflammatory responses (Bakinowska et al., 2024), hormonal signaling pathways (Neufeld et al., 2024), and other mechanisms affecting skeletal muscle metabolic balance (Li et al., 2024). Studies have shown that aging or declining hormone levels are often accompanied by reduced microbial diversity, a decrease in beneficial bacteria such as Lactobacillus and Bacteroides, and an increase in pathogenic bacteria like Enterobacter (Picca et al., 2018). This microbial dysbiosis is frequently associated with a loss of muscle mass and decline in muscle function. Conversely, supplementing with probiotics or enhancing microbial diversity has shown promise in improving muscle function (Chen et al., 2022). Thus, targeting the gut microbiota has emerged as a potential intervention strategy. However, studies investigating how estrogen deficiency alters gut microbiota and how such changes impact skeletal muscle remain limited, particularly regarding whether these alterations can be modulated through lifestyle interventions.

Aerobic exercise, as a safe, cost-effective, and efficient non-pharmacological intervention, has been widely adopted to prevent and alleviate muscle loss in postmenopausal women (Khalafi et al., 2023; Tan et al., 2023). Research has shown that aerobic exercise can activate skeletal muscle protein synthesis pathways, such as the Akt/mTOR signaling pathway, inhibit protein degradation pathways including FOXO3a/Atrogin-1, and promote muscle protein anabolism (Zeng et al., 2020). Moreover, aerobic exercise can improve metabolic status and modulate gut microbiota diversity and composition, thereby restoring microbial homeostasis (Quiroga et al., 2020). Recent studies further suggest that regular exercise may enhance the expression of aromatase in skeletal muscle, promoting local estrogen synthesis and providing intrinsic hormonal support for muscle maintenance (Shi et al., 2019). However, most existing studies have focused on either muscle tissue or gut microbiota independently, and few have systematically investigated how aerobic exercise regulates the “gut microbiota–skeletal muscle” axis under estrogen-deficient conditions.

Therefore, this study employed an ovariectomized mouse model to comprehensively investigate the effects of aerobic exercise on skeletal muscle mass and gut microbiota composition under estrogen-deficient conditions. We evaluated changes in aromatase expression and protein synthesis/degradation signaling pathways in muscle, and further analyzed the correlations between gut microbiota diversity and skeletal muscle function. These findings are expected to provide both theoretical insights and practical guidance for maintaining muscle health in postmenopausal women, offering important implications for both basic and applied research.

This study, based on an estrogen-deficient mouse model, systematically evaluated the regulatory effects of aerobic exercise on skeletal muscle function and gut microbiota. The results demonstrated that 8 weeks of aerobic exercise significantly improved muscle mass and function in ovariectomized (OVX) mice, restored gut microbiota composition, upregulated aromatase expression and local estrogen levels in skeletal muscle, activated protein synthesis pathways, and suppressed protein degradation. Moreover, microbial diversity was significantly correlated with muscle function, suggesting that the “gut microbiota–skeletal muscle” axis may represent a critical regulatory pathway.

Aerobic exercise, as a non-pharmacological intervention, has been widely demonstrated to improve gut microbiota composition (Resende et al., 2021). Studies have shown that regular physical activity can promote the colonization of probiotics (such as Lactobacillus and Bacteroides) and suppress the overgrowth of pathogenic bacteria by enhancing intestinal peristalsis, improving intestinal barrier function, and reducing systemic inflammation, thereby increasing microbial diversity and restoring metabolic homeostasis (Aragón-Vela et al., 2021; Dmytriv et al., 2024). In the present study, 8 weeks of aerobic exercise significantly altered the gut microbial composition of OVX mice, restoring the relative abundance of beneficial phyla such as Bacteroidota, suggesting that exercise may regulate skeletal muscle function through the “gut–muscle axis”. Notably, aerobic exercise markedly increased gut microbial diversity in the OVX group but not in sham-operated mice, suggesting a differential response based on estrogen status. Estrogen deficiency disrupts gut barrier integrity and microbial homeostasis, making OVX mice more responsive to exercise-induced microbial restoration. In contrast, the sham group maintains a relatively stable microbiota, with exercise exerting only minor structural adjustments. These findings imply that the divergent microbial changes result from distinct host–microbiota interactions under different hormonal conditions. In addition, microbial-derived short-chain fatty acids (e.g., acetate and butyrate) have been reported to activate the AMPK pathway and inhibit histone deacetylases, thereby promoting protein synthesis and mitochondrial biogenesis in skeletal muscle (Hu et al., 2018; Frampton et al., 2020). This may represent an indirect mechanism by which exercise improves muscle function. Furthermore, our findings revealed that exercise markedly upregulated aromatase expression in skeletal muscle, accompanied by an increase in local E₂ levels. Previous studies have indicated that aromatase expression is regulated by transcription factors such as AMPK and PGC-1α, which can be activated by exercise (Zhang et al., 2024). Exercise-induced upregulation of aromatase may enhance local estrogen synthesis in muscle, facilitating muscle fiber repair and functional recovery (Pellegrino et al., 2022; Seibert et al., 2024), suggesting that skeletal muscle may act as a target-like tissue for exercise-induced local estrogen production. In support of this, we observed increased aromatase expression and estrogen levels in skeletal muscle following exercise, suggesting a potential for local synthesis (Shi et al., 2019). However, due to the lipophilic nature of steroid hormones and the rich vascularization of muscle tissue, passive uptake from peripheral circulation cannot be excluded (Miller and Auchus, 2011). Moreover, the current analytical methods are insufficient to determine the exact origin of intramuscular estrogen. Future studies could consider muscle-specific knockout models, local inhibition strategies, or metabolic tracing techniques to further clarify the source.

In recent years, growing evidence has suggested that the gut microbiota can influence skeletal muscle mass by regulating energy metabolism, mitochondrial biogenesis, and inflammatory responses through its metabolites, such as short-chain fatty acids and secondary bile acids (Imdad et al., 2022; Lian et al., 2022). This relationship is particularly relevant under conditions of estrogen deficiency, where a decline in microbial diversity is closely associated with sarcopenia. Guo et al. demonstrated in an ovariectomized mouse model that dysbiosis of the gut microbiota is strongly linked to enhanced muscle protein degradation, while probiotic supplementation can significantly improve muscle function (Guo et al., 2023). More importantly, we observed that aerobic exercise markedly upregulated aromatase expression in skeletal muscle, along with a recovery in local E₂ levels, suggesting that skeletal muscle may serve as a peripheral estrogen-producing organ in response to exercise. The expression of aromatase in muscle tissue can be activated by exercise, potentially through the ERK/CREB signaling pathway, thereby enhancing local estrogen synthesis (Mori et al., 2019). Emerging evidence indicates that endurance training exerts bidirectional regulatory effects on both skeletal muscle and the gut microbiota. On one hand, aerobic exercise can enhance local estrogen signaling in skeletal muscle by upregulating intramuscular aromatase expression and activating the PI3K/Akt/mTOR pathway, thereby promoting muscle regeneration in estrogen-deficient models (Saponaro et al., 2024). On the other hand, endurance exercise is known to increase gut microbial diversity and alter community structure, influencing host endocrine and metabolic responses. For example, Zhang et al. demonstrated that sustained high-intensity aerobic training improved muscle performance via a gut microbiota–testosterone axis in mice, confirmed through microbiota transplantation experiments (Zhang L. et al., 2022). Similarly, Marsh et al. reported that aerobic exercise enhanced metabolic and muscular health in ovariectomized mice, linked to modulation of both systemic hormone levels and gut microbial composition (Marsh et al., 2023). These findings support the existence of an integrated muscle–gut–endocrine axis through which physical training mediates coordinated adaptations in hormonal balance and skeletal muscle function.

Although this study preliminarily revealed the multifaceted beneficial effects of aerobic exercise on skeletal muscle and gut microbiota in an estrogen-deficient mouse model, several limitations should be acknowledged. First, the current findings are based on correlation analyses, and causal relationships were not verified using strategies such as fecal microbiota transplantation, antibiotic-mediated microbiota depletion, or single-strain probiotic supplementation (Rosshart et al., 2019). Second, the precise source of estrogen synthesis remains unclear, and whether increased aromatase expression directly contributes to elevated local E₂ production requires further investigation. Third, as this study was conducted solely in a mouse model, the translational relevance to humans—particularly postmenopausal women—needs to be validated through clinical samples and intervention studies. In the future, integrative multi-omics approaches, including metabolomics and transcriptomics, may help to elucidate the specific molecular and metabolic mechanisms underlying the interplay among exercise, gut microbiota, hormones, and skeletal muscle.

This study demonstrates that ovariectomy-induced estrogen deficiency leads to reduced skeletal muscle mass and function in mice, accompanied by decreased gut microbiota diversity. An 8-week aerobic exercise intervention effectively ameliorated these abnormalities by enhancing muscle quality and fatigue resistance, modulating protein metabolism–related signaling pathways, and reshaping gut microbiota composition. These findings suggest that exercise may exert synergistic effects through the “gut microbiota–skeletal muscle” axis, offering a potential intervention strategy for the prevention and management of menopause-associated sarcopenia.