Age is a significant determining factor in testosterone release. Before puberty the concentrations of testosterone are low as would be expected. After this time there is a small increase in levels in females, but a large increase in males. This provides men with their secondary sexual characteristics. Testosterone levels in men stay broadly similar until around 35 after which levels are thought to decrease approximately 1.6 % for total testosterone and 2-3 % for free testosterone per year. Therefore as age progresses, resting levels of testosterone can fall significantly to low levels. In women testosterone levels fall gradually until menopause and then decrease up to 60 % within 2 to 5 years. Resistance training does not appear to cause large increases in testosterone release in school age or college aged males and this may relate to the fact that their levels are already high. Resistance training also does not cause large elevations in testosterone in women. However, in young men the lack of effect may be methodological, and may be explained by the fact that the resistance training they were exposed to was not intense enough to elicit a testosterone response. This is evidenced in elite lifters of the same age range who have been observed to experience testosterone increases from resistance training. In middle aged and older men, resistance training can elicit a significant elevation in testosterone, something that is highly apparent for free testosterone. This may relate to the fact that resting levels of testosterone in these individuals is lower and so the response to exercise is relatively large considering the baseline levels.
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Vingren, J. L., Kraemer, W. J., Ratamess, N. A., Anderson, J. M., Volek, J. S. and Maresh, C. M. 2010. Testosterone physiology in resistance exercise and training: the up-stream regulatory elements. Sports Medicine. 40: 1037-1053
