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Hard physical training requires massive amounts of energy and sustained mental focus. Caffeine has been employed as an ergogenic in athletics for many years – from recreational bodybuilders to competitive athletes. The substance positively affects time-to-exhaustion and endurance-training potential. Caffeine has a large number of reported physiological benefits to athletes; such as greater muscle contractions from antagonistic actions on adenosine receptors, delayed fatigue by stimulating the central nervous system, direct neuro-endocrine activation and direct actions on skeletal muscle function. It has been shown to support endurance athletes engaged in strenuous cycling, running and swimming. Caffeine has also been shown to improve performances in intermittent high-intensity team sports.

The stimulant’s role in bodybuilding is an area less explored in clinical research; even so, a positive relationship between caffeine intake and muscle growth has been hypothesized for some time now. To clarify caffeine’s affects on anabolism, researchers from the Institute of Sport and Recreation Research Horticulture and the Food Research Institute of New Zealand published a study in the International Journal of Sport Nutrition and Exercise Metabolism, April 2008. The researchers examined hormonal responses to caffeine intake during resistance training. The 24 previously conditioned participants were members of a professional rugby team. The study aimed to identify the effects of caffeine on testosterone and cortisol responses to resistance exercise.

Testosterone is known as the primary anabolic hormone responsible for strength and muscle gains. It is also known to increase in response to resistance training. This male hormone stimulates events that increase the production of contractile proteins – a requirement for greater musculature. Opposing testosterone is cortisol, an adrenal hormone known to cause protein breakdown. Cortisol also rises in response to exercise, triggered from an alarming increase in metabolic demands within an athlete’s body. The ratio of testosterone to cortisol determines an athlete’s relative anabolic or catabolic state. Greater testosterone provides an enhanced environment for muscle growth. This is one of the many reasons exogenous administration of supra physiological amounts of testosterone amplifies training efforts by bodybuilders.

In the New Zealand study, caffeine doses of 0, 200, 400 and 800 milligrams were used. To measure the changes in hormones, saliva samples were obtained from each participant at the time of caffeine ingestion, before resistance exercise, every 15 minutes during training, as well as 15 and 30 minutes post workout. Participants were advised to not brush their teeth or drink hot beverages within two hours of the assessment.

Exercise alone raised testosterone by 15 percent during training. 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.

In the study, testosterone and cortisol raised in relationship to the amount of caffeine administered. 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.

The fascinating finding from this study is the clear relationship between caffeine intake and testosterone levels during resistance training. 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. A large dose can sway the testosterone-to-cortisol ratio to favor protein breakdown, with a long-lasting effect on plasma cortisol concentrations. Habitual intake and individual tolerance are also important considerations for optimal performance doses. Caffeine’s ergognic effect seems to be best acquired at doses around 400 to 600 milligrams.

Caffeine as an ergogenic is effective and safe with reasonable use. Despite short-term alterations in some cardiovascular variables, no long term effects on blood pressure, heart rate or plasma rennin activity have been recorded in clinical studies. In healthy individuals, caffeine doses up to 400 milligrams are well tolerated. In contrast, doses beyond 400 milligrams begin to significantly increase systolic and diastolic blood pressure, as well as complaints of palpitations, anxiety, headache, restlessness and dizziness. Athletes should gradually increase doses of caffeine over 400 milligrams, to assess individual tolerance and sensitivity. In adults, the short-term lethal dose for caffeine is estimated at five to 10 grams per day (intravenously or orally), which is equivalent to 75 cups of coffee, 125 cups of tea or 200 cola beverages. Sensible caffeine intake has little or no negative physiological consequences in healthy individuals.

Caffeine is an adrenergic stimulant that produces a thermogenic effect, events that increase fat oxidation and body temperature. Proper hydration and electrolyte balances must be considered when supplementing an aggressive training routine with caffeine.

It seems evident that future research will continue to build on this New Zealand study. At the moment, moderation is paramount when using caffeine to boost testosterone production during resistance training. Equally important, increases in cortisol must be addressed immediately after training – especially following heavy caffeine use – using post-workout nutrition and relaxation tactics.

Beaven, Hopkins, Hansen, Wood, Cronin, Lowe. Dose Effect of Caffeine on Testosterone and Cortisol Responses to Resistance Exercise, IJSNEM, Vol. 18, Iss. 2, April 2008.