In a more recent study, Marin et al. (2006) found that exercise also increased testosterone levels in men. Men who participated in this study had their testosterone level tested prior to exercising and then again after performing lat pulls, bench presses, leg curls, leg extensions, leg presses, and military presses. Immediately after exercising the mens' testosterone levels were significantly raised, but then dropped back to baseline levels after 20 minutes had passed. From the studies described above it appears that exercising may increase testosterone levels, but that increased testosterone levels drop back to baseline levels shortly after the exercise is over. However, there are also a few studies that show that exercising decreases testosterone levels in men after exercise (e.g., Wheeler, 2003) and so the jury is still out as to whether or not exercise can increase testosterone levels.
Marin, D. P., Figueira, A. J. Jr., and Pinto, L. G. (2006). One Session of Resistance Training May Increase Serum Testosterone and Triiodetironine in Young Men? Medicine and Science in Sports and Exercise 38: S285.
Wheeler, G. D., Singh, M., Pierce, W. D., Epling, W. F., and Cumming, D. C. (1991). Endurance training decreases serum testosterone levels in men without change in luteinizing hormone pulsatile release. Journal of Clinical Endocrinology and Metabolism 72: 422-425.