Cyclists given 4 weeks of zinc supplementation were shown to have higher total and free testosterone levels after exhaustive exercise. However, resting testosterone levels were not boosted by taking zinc supplements. The cyclists were given 30mg of zinc per day by researchers.
Shafiei Neek L, Gaeini AA, Choobineh S (2011). Effect of Zinc and Selenium Supplementation on Serum Testosterone and Plasma Lactate in Cyclist After an Exhaustive Exercise Bout. Biol Trace Elem Res.