This is something I've written about several times.
Here, from a relatively recent article:
"It seems counterintuitive, but male athletes typically have lower Testosterone levels than couch potatoes!
Comparative studies have shown again and again that free and total T concentrations in chronically trained athletes (runners, weight lifters, rowers, cyclists, and swimmers) are surprisingly low. In fact, the Testosterone levels of trained subjects were only 60-85% of untrained men.
While FSH and LH levels of trained men did not differ from untrained men, T levels were significantly affected. Some researchers attribute the discrepancy to alterations in hepatic and extrahepatic (muscles, skin) metabolism of Testosterone, which can?t be compensated for by the athletes? gonads.
And, while exercise of any kind for as little as 5-30 minutes results in a significant increase in Testosterone, levels decline below baseline 15-60 minute later. What?s more, this reduction below baseline can last up to three days, depending on the duration and intensity of the exercise!
So does this mean that fat bastards are more virile than rock-hard athletes? God I hope not."
References: Arce, et al, 1993, Hackney, 1988; Wheeler, et al ,1984, 1991.
More specifically, Hackney, Comparison of resting reproductive hormonal profiles in select athletic groups, Biol Sport, 4:200-204.
If you need more, let me know.