I was over at Border's Book store. The August Muscular Development magazine had a good article on how caffeine increases testosterone production. So, I looked it up on line. This is interesting.
http://www.warriorfx.com/2008/03/caffei ... -exercise/
"Caffeine at doses of 400 milligrams or more tended to cause a small decrease in testosterone after ingestion, but a rapid increase in testosterone began within 15 minutes of exercise.
The result was significantly greater than the exercise-only prescription. A hefty 800-milligram caffeine dose produced a 61 percent average increase in testosterone after 60 minutes of resistance training!
Adversely, the large dose also resulted in a 51-percent raise in cortisol over the exercise period, which continued to elevate to 93 percent over baseline during the short 30-minute recovery phase post workout.
When the results for exercise and recovery periods were averaged out, the 800-milligram dose raised testosterone 39 percent – in which 21 percent was attributed to the caffeine intake
. However, the peak dose also resulted in a 52 percent average increase in cortisol during exercise and recovery, when compared to exercise alone.
Caffeine can amplify the training-induced secretion of this important anabolic hormone, in a dose-dependent manner. More specifically, doses of 400 milligrams or more exhibited the greatest potential to increase testosterone. But increased doses are also met with an increase in testosterone’s catabolic nemesis: cortisol."
The Muscular Developement article noted the increase in cortisol, as well. However, it went on to say that cortisol can be countered/shut down by consuming carbohydrates.
Nutritionist have stated that is one of the benefits of consuming a post workout carbohydrate drink. A protein-carbodhyrate drink is anti-catabolic...it shuts down cortisol.
Caffeine is used in Excedrin and other pain killers, as you probably know. Another point of the MD article was the basically caffeine numbs any pain during your workout...or as they put it, "caffeine increases you pain tolerance." Thereby, allowing one to workout harder.