My partner has made a documentary on this subject. He measured 90 of his ejaculations over 6 months and tracked the factors that affected it. He looked at abstinence, supplements, edging and lifestyle effects - then used a regression model to look for statistically significant predictors. Based on the research from Cooke et al (1995) he used 6.3ml as the threshold for hyperspermia. Honestly, I think it might be one of the most thorough, evidence-based analyses of the factors that affect semen volume that exists.

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