Caffeine is quite possibly the most consistently used drug in the world. With the ability to abolish fatigue and increase wakefulness, caffeine makes the world go ‘round. Everyone from truck drivers, airline pilots, soldiers or even surgeons like me bank on caffeine at some point. Caffeine’s effects last for up to six hours, and some people may become so dependent that they experience withdrawal symptoms of fatigue, headaches and flu-like symptoms when they forget their cup o’ joe in the morning.

Caffeine is heavily used in sports nutrition products intended for fat loss and pre-workout stimulation. There are numerous studies that suggest that caffeine can improve power and strength performance and endurance.^1,2 Though, the more ambiguous results seen in a few studies could be related to methodological errors and problems with test-subject controls.

For instance, some studies try to clear caffeine from the system prior to the study, which may just lead to a recovery from withdrawal symptoms rather than enhancement of performance. Although withdrawal itself doesn’t seem to cause a sports performance deficit, it certainly causes headaches, fatigue, loss of short-term memory and mood depression. Furthermore, some research studies may not account for test subjects who regularly use caffeine or may even be, dare I say, naïve to its effects, therefore making them more sensitive to its effects. Either way, this leads to confounding variables that result in inconsistent results across the board.

Studies suggest that a relatively low dose of 3 milligrams per kilogram of bodyweight is adequate to experience performance-enhancing benefits. In a 150-pound person, that is only ~200 milligrams of caffeine. Interestingly, despite performance enhancement, very little metabolic changes occur at this dose. Based on a few studies, it seems that the better seasoned you are as an athlete, the more effective acute doses of caffeine seem to become.⁶ Doses of 6 milligrams per kilogram are more commonly used, and may be more effective for strength athletes (400 mg of caffeine for a 150-pound person). Exceeding these doses may lead to unpleasant jitters, nausea and difficulty focusing on tasks.

Questions About Timing

The timing of caffeine consumption is a hot topic of debate, as it is really uncertain from human studies as to how caffeine actually improves performance. In the case of endurance athletes, it is thought that they enhance mobilization of fats from stores and thus provide more fuel for muscles to burn. Muscle glycogen is spared in moderate exercise after ingestion of caffeine at 5 to 9 milligrams per kilogram of bodyweight. There is little evidence to support a metabolic component like this for enhancing performance at a low caffeine dose (3 mg/kg). Thus, it appears that alterations in muscle metabolism alone cannot fully explain the ergogenic effect of caffeine during endurance exercise in low doses.

To put this into perspective, 3 milligrams per kilogram of bodyweight of caffeine is equivalent to approximately two cups (~8 oz) of coffee; and 9 milligrams per kilogram equals approximately five to six regular size cups of coffee. It is important to note that we all metabolize and respond to drugs differently; you may have to experiment with the right dose for your training.

In addition to ergogenic effects on endurance exercise, caffeine has been shown to increase performance in 60- to 180-second sprints and high-intensity intermittent exercise.¹ Since this type of exercise rarely involves the use of fat for fuel, the mobilization of fat to spare glycogen theory doesn’t work well for caffeine’s ability to improve short duration performance. Science suggests that caffeine’s effects on the central nervous system may play a significant role here.³ The arousal effects and even a slight blunting of pain perception that comes with caffeine may explain the ability to push harder in short-duration activities (i.e., maximal lifting or sprinting).

In reality, it is very difficult to determine the effects of caffeine on human muscle. Studies in animals and isolated muscle preparations have provided us some insight into how caffeine enhances performance. At physiological concentrations, caffeine appears to increase the ability of muscle to produce work, force and power. It may even be that caffeine increases the performance of slow-twitch endurance muscle fibers two times more than fast-twitch strength fibers (increased by 6% and 3%, respectively).⁷ This may be an explanation for improvements in endurance training and competition. Given at high enough doses in muscle tissue preparations, it appears that caffeine can actually make muscle contract without direct stimulation.⁶ How caffeine does this is still being explored.

The timing of caffeine consumption is also up for debate. First of all, caffeine consumption in the form of coffee or other liquids seems to be more rapidly absorbed than pill form. Thus, you can get caffeine into your system with a peak at ~40 minutes versus ~60 minutes as a pill.⁸ Further, it seems that the effects of caffeine work longer in non-regular consumers of caffeine beverages. In one study, the effects of 5 milligrams per kilogram of bodyweight lasted up to six hours in non-regular consumers, versus only one to three hours in regular consumers.⁹ Based on these results, it seems it would be best to have your caffeine at ~6 milligrams per kilogram (400 mg, or a Grande to Venti coffee) about one hour before your training.

Safety Concerns

Editorials in medical journals such as the Journal of the American Medical Association have warned of excessive use of caffeinated beverages, especially as mixers in alcoholic beverages.⁴ Alcohol and certain medications can prolong the otherwise normal five-hour half-life of caffeine, thus increasing chances of toxicity. It is suggested that 3 to 10 grams (140mg/kg bodyweight) of caffeine consumed in a brief period of time could be lethal. This would be about 75 cups of coffee, or 200 cans of Coke. It’s notable that prospective longitudinal studies have shown no increases in cardiovascular disease risk with up to six cups of regular coffee per day.⁵

Caffeine is also a diuretic and can increase urine output within one hour of consumption. If there is a chance that you may be dehydrated (i.e., warm weather training), caffeine consumption should be limited until adequate hydration is available. Studies performed by the United States military on the safety of regular caffeine usage by soldiers demonstrated relative safety of caffeine dosed between 100 to 600 milligrams.⁵ It is recommended that a 600-milligram limit not be exceeded, unless strongly habituated to the use of caffeine. When consuming close to 600 milligrams of caffeine per day, it should be divided into two to three servings throughout the day. When taking any new supplements containing caffeine, you should attempt a “tolerance test.” That is, you should try taking half or less of the serving size on first try, to test for any adverse reactions. If you tolerate the partial dose, slowly increase it until the desired effect is obtained.

Caffeine can be an essential component to a successful training regimen, especially when you’re too tired to even go to the gym. Caffeine consumption (3-9 mg/kg) prior to exercise increases performance during endurance and short-term, intense exercise. Caffeine can help you increase your training efficacy and recovery. Caffeine supplements are an especially great way for physique athletes to boost their training when dieting for a competition. As with any supplement, caffeine must be used in moderation to avoid potentially serious side effects. Strictly avoid mixing energy drinks into your alcoholic cocktails. Use your caffeine supplements to excite your mind and body in the gym, not the bar.

References:

Davis JK, Green JM. Caffeine and anaerobic performance: ergogenic value and mechanisms of action. Sports Med 2009;39(10):813-32.

Burke JM. Caffeine and sports performance. Appl Physiol Nutr Metab 2008;Dec;33(6):1319-34.

Motl RW, et al. Effect of caffeine on leg muscle pain during cycling exercise among females. Med Sci Sports Exerc 2006; 38: 598-604.

Sepkowitz KA. Energy Drinks and Caffeine-Related Adverse Effects. JAMA 2013;309(3):243-244.

Committee on Military Nutrition Research, Caffeine for the Sustainment of Mental Task Performance: Formulations for Military Operations. National Academy Press Washington DC 2001.

Tallis J, et al. What can isolated skeletal muscle experiments tell us about the effects of caffeine on exercise performance? Br J Pharmacol 2015 Aug;172(15):3703-13.

Tallis J, et al. The effect of physiological concentrations of caffeine on the power output of maximally and submaximally stimulated mouse EDL (fast) and soleus (slow) muscle. J Appl Physiol (1985). 2012 Jan;112(1):64-71. J Appl Physiol (1985). 2012 Jan;112(1):64-71.

Liguori A, et al. Absorption and subjective effects of caffeine from coffee, cola and capsules. Pharmacol Biochem Behav 1997 Nov;58(3):721-6.

Bell DG, McLellan TM. Exercise endurance 1, 3, and 6 h after caffeine ingestion in caffeine users and nonusers. J Appl Physiol (1985). 2002 Oct;93(4):1227-34.