Does intense weight training increase testosterone levels? Common sense would indicate that it does, simply because of the imposed exercise stress on working muscles. Since testosterone is known to support muscular growth, it seems logical that intense bodybuilding exercise would lead to a rise in testosterone levels. The scientific literature on the subject, however, is inconclusive, with some studies showing a rise in testosterone levels following exercise and others showing a decline.
A drop in blood testosterone isn’t hard to understand if you look at intense workouts as a form of stress. Any type of stress leads to the release of stress-modulating hormones, such as epinephrine, norepinephrine and cortisol. Cortisol, which is synthesized in the adrenal gland cortex, is a major catabolic hormone that, among other functions, directly opposes the anabolic effects of other hormones, such as testosterone and growth hormone. In effect, when cortisol is elevated’as it is during stressful conditions’testosterone is lowered. And exercise is one of those conditions.
But the exercise-related hormone-secretion scenario isn’t as simple as it appears. That’s illustrated in a new study involving 10 young, healthy men, average age 21, who engaged in an intense weight-training program featuring 50 sets of upper- and lower-body exercises involving all major muscle groups.1 The subjects all followed the same diet, consisting of 55 percent carbs, 15 percent protein and 30 percent fat, with calories adjusted for individual body size.
The subjects trained in the afternoon, after which the researchers took their blood samples every 10 minutes for the next three hours, testing for luteinizing hormone (LH), a pituitary hormone that controls testosterone synthesis in the body and is secreted in bursts. They checked for other hormones, including free and total testosterone and cortisol, every hour for 13 hours after training.
Levels of total and free testosterone declined overnight, while the production rate of LH dropped 24 percent in the hours following exercise. Cortisol levels rose, especially three hours after the workout. The decline in testosterone was caused by the drop in LH activity.
As to what caused the drop in LH activity, the authors explain that the exercising subjects might not have been getting enough calories to cover the cost of the intense exercise sessions. Both insufficient calories and fasting are considered highly stressful, leading to blunting the release of certain hormones, including testosterone.
The drop in testosterone may also have occurred as a means of marshaling extra calories by using more stored fat following exercise. The body is in a catabolic state after exercise, and it needs extra calories to power restorative processes like upgraded protein and glycogen synthesis in muscle. Apparently, the lowered testosterone allows cortisol to mobilize extra fat for that purpose. The elevated cortisol level also blunts LH secretion. Testosterone levels return to normal within 24 hours.
Two unanswered questions raised by this study: What happens if you train every day? Do daily trainees have chronically depressed testosterone levels? IM
Editor’s note: Muscle-Link’s Cort-Bloc can help control muscle-wasting cortisol. For more information see page 234 of the March ’02 IRONMAN.
1 Nindl, B.C., et al. (2001). LH secretion and testosterone concentrations are blunted after resistance exercise in men. J Appl Physiol. 91:1251-1258.