Microcurrent Neuromodulation and Stress–Recovery Markers Across a Competitive Season in Elite Female Soccer Athletes: A Controlled Pilot Study

Background: Elite women’s soccer involves sustained physical and psychosocial demands that may affect endocrine regulation, autonomic recovery, and sleep across the competitive season. Non-invasive neuromodulation has been proposed as an adjunct recovery strategy; however, longitudinal in-season evidence in elite female athletes remains limited. Methods: This controlled pilot trial included 12 elite female soccer players (mean age of 21.4 ± 5.2 years), allocated in a 1:1 ratio to a NESA intervention group (n = 6) or a no-intervention control group (n = 6). The intervention consisted of 32 sessions delivered over eight weeks, with four sessions per week and no sessions on match days. Outcomes were assessed at five predefined time points across the competitive season. Primary physiological outcomes were salivary cortisol and heart rate variability (HRV), complemented by subjective sleep quality (PSQI), competitive state anxiety (CSAI-2), and menstruation-related quality of life (CVM-22). Results: All participants completed the protocol, and no adverse events were reported. The main finding was observed at the post-intervention assessment (M4), where salivary cortisol concentrations were significantly lower in the NESA group than in the control group (7.62 ± 4.02 vs. 25.90 ± 9.92 µg/dL; independent Student’s t-test, t = −4.184, df = 10, p = 0.002). Subjective sleep quality showed divergent descriptive trajectories during the pre–post intervention interval: PSQI scores decreased in the NESA group from M3 to M4 and increased in the control group, although the between-group comparison of change was not statistically significant (p = 0.183). Continuous HRV indices did not show a consistent pattern favouring the NESA group; however, categorical HRV profiles suggested descriptive maintenance of a high HRV classification in the intervention group. No consistent intervention-related effects were observed for competitive state anxiety or menstruation-related quality of life. Conclusions: In this controlled pilot study, an eight-week NESA non-invasive neuromodulation protocol was associated with lower post-intervention salivary cortisol concentrations in elite female soccer players. Sleep and HRV findings should be interpreted as complementary descriptive signals, whereas anxiety and menstruation-related quality of life did not show consistent intervention-related changes. Given the small sample size, open-label design, absence of a sham control, and unadjusted baseline differences in cortisol concentrations and sleep quality between groups, these findings should be considered preliminary and hypothesis-generating. Larger, adequately powered, sham-controlled trials are needed to determine the magnitude, specificity, and practical relevance of these findings.