Endogenous transient doping: physical exercise acutely increases testosterone levels—results from a meta-analysis

Purpose: Although endogenous testosterone levels are demonstrated to be affected by both acute exercise and resistance training, the dynamic regulation of androgen production after physical activity is still a matter of debate. This meta-analysis was designed to assess whether physical exercise acutely affects testosterone levels in men. Methods: The literature search was conducted to identify longitudinal trials evaluating the acute change of both total testosterone (TT) and free testosterone (fT) after physical activity in adult men. Sensitivity analyses were performed considering the sample collected (blood or saliva), the intensity of the physical exercise and the interval between the end of the exercise and the sample collection. Results: Forty-eight studies were included in the analysis, accounting for 126 trials. A total of 569 patients were enrolled (mean age 29.7 ± 13.1 years). The physical activity increased acutely TT (standardized mean difference 0.74, 95%CI: 0.56, 0.91 nmol/L), considering both serum and saliva samples (p < 0.001). Testosterone increased after moderate (p < 0.001) and high-intensity (p < 0.001) exercises, but not after mild physical activity (p = 0.19). Moreover, the testosterone increase was evident when measured immediately at the end of the exercise and within 30 min (p < 0.001), but not after 30 min (p = 0.930). Similar significant results were obtained considering fT, while SHBG did not change after physical activity (p = 0.090). Conclusion: The comprehensive evaluation of the acute physical activity effect on testosterone levels identified a clear increase after exercise, irrespective of the sample collected. The main determinant of this fluctuation was the exercise intensity, with a mechanism that seems to be mostly SHBG independent. In particular, moderate/intense physical activity resulted able to increase endogenous androgenic production, albeit acutely and transitory. Trial registration number: PROSPERO registration ID: 157348.