Semen Quality and Metabolic Biomarker Changes Following a 12-Week Combined Exercise Program in Healthy Adult Men: A Non-Randomized Controlled Intervention Study

Background/Objectives: Male reproductive health is increasingly considered an integrated physiological outcome influenced by lifestyle, body composition, metabolic status, and endocrine regulation. This study examined changes in semen quality, body composition, glucose metabolism, and reproductive hormonal profile associated with participation in a 12-week combined exercise program in healthy adult men. Methods: Thirty-four healthy men aged 18–24 years were included in a two-arm, non-randomized, parallel-group controlled intervention study and were allocated, according to their willingness and availability rather than by randomization, to either an exercise group (n = 17) or a passive control group (n = 17). The exercise group completed a supervised combined aerobic and resistance exercise program three times per week for 12 weeks, whereas the control group maintained usual lifestyle habits and did not participate in structured exercise. Outcomes were assessed at baseline and week 12. Body composition, fasting glucose, fasting insulin, HOMA-IR, reproductive hormones, conventional semen parameters, and predefined derived semen indices were analyzed. Conventional semen parameters were the primary outcomes; body composition, glucose-metabolism, and hormonal markers were secondary outcomes; and derived semen indices were exploratory. Time × group interactions were evaluated using two-way mixed repeated-measures ANOVA. Between-group differences in change are reported with 95% confidence intervals (CIs), and a Holm–Bonferroni sensitivity analysis was applied across the 20 interaction tests. The study was registered at ClinicalTrials.gov ([NCT07778576]). Results: Significant time × group interactions were observed for BMI, body fat percentage, fasting glucose, fasting insulin, and HOMA-IR, favoring the exercise group. Total testosterone and sex hormone-binding globulin increased, whereas estradiol and prolactin decreased in the exercise group; follicle-stimulating hormone and luteinizing hormone remained unchanged. Semen volume, sperm concentration, total motility, progressive motility, total sperm count, total motile sperm count, and progressive motile sperm count improved in the exercise group compared with the control group (e.g., between-group difference in change in progressive motility: 4.55 percentage points, 95% CI 3.66 to 5.44; total motile sperm count: 5.60 million, 95% CI 2.18 to 9.02). No significant interactions were observed for non-progressive motility or Kruger strict morphology. After Holm–Bonferroni adjustment, the interactions for semen volume, total sperm count, and estradiol were no longer statistically significant. Conclusions: A 12-week combined exercise program was associated with favorable metabolic, hormonal, and selected semen-quality changes in healthy adult men. Given the non-randomized design, small sample size, single semen sample at each time point, and absence of fertility endpoints, these findings should be interpreted as preliminary and hypothesis-generating rather than evidence of clinical reproductive benefit.