Caffeine: The Key To Unlocking Your Workout

Caffeine (1,3,7-trimethylxanthine) is the most widely consumed drug in the world and is commonly used by athletes, both recreational and professional, for performance enhancement.   In the United States, over 70% of caffeine intake comes from coffee, followed by soft drinks and tea, although energy drinks and sports gels and chews containing caffeine are quickly gaining popularity for use before and during competition. Caffeine is also frequently found in pre-workout supplements and weight loss products, often in multiple forms.  With caffeine use so widespread among athletic populations, one must question its effectiveness in terms of improving sports performance, and also whether there are any negative side effects from acute (short-term) or chronic (long-term) consumption.

Caffeine is absorbed rapidly by the gastrointestinal tract and enters the bloodstream within 15-45 minutes of consumption, with peak blood concentrations evident about one-hour post-ingestion.  Its rapid absorption rate makes caffeine an effective pre-workout supplement, since it doesn’t need to be “loaded” for days or weeks, and you can take it in a targeted manner just before a competition or training session. Many consume caffeine for its effects as a central nervous system (CNS) stimulant in order to increase focus and alertness, but there is also evidence that the benefits of caffeine supplementation extend beyond these effects, specifically prolonged endurance, increased metabolic rate, enhanced fat metabolism and improved neuromuscular function.

What are the Performance Benefits?

Improvements in endurance performance following caffeine intake have been observed consistently in events lasting 15-120 minutes at an intensity of 70-75% VO2max, in time trial performances (simulating competitive events such as the 10k), and in time to exhaustion tasks in cycling and running.  A possible explanation for these improvements may be that caffeine alters substrate utilization (energy source) during exercise by decreasing reliance on glycogen (carbohydrate stores) and increasing dependence on fat stores, the latter of which is we have in relative abundance in our bodies compared to glycogen. However, recent studies have brought this theory under scrutiny.  Another proposed explanation for the endurance benefits of caffeine consumption is that it decreases pain perception, thus lowering the rate of perceived exertion (RPE) at a given work rate, and making the discomfort of fatiguing exercise seem more tolerable.  Either way, extensive research exists supporting the ergogenic effect of caffeine on aerobic endurance.

Furthermore, both habitual users and non-users alike appear to reap the benefits of caffeine supplementation on endurance performance.  In a study measuring aerobic endurance in a time to exhaustion cycling test at 1, 3, and 6 hours after caffeine consumption (6 mg/kg body weight), both users (habitually consuming ≥ 300 mg/day) and nonusers (consuming ≤ 50 mg/day) showed significant performance improvements with caffeine; however, nonusers demonstrated a more prolonged treatment effect, up to 6 hours post-ingestion, whereas habitual users only demonstrated a significant increase in performance at 1 and 3 hours post-ingestion. So, depending on the duration of your event, caffeine supplementation may be more effective when taken just prior to competition, and not on a regular basis.  Alternatively, repeated doses can be taken throughout an event lasting more than 3 hours to prolong the effects of caffeine.

The evidence supporting caffeine supplementation in strength and power athletes is not as extensive, although research has demonstrated that it may result in improved neuromuscular function and muscular contraction. Effects on maximal strength (1RM) have thus far been inconsistent, but caffeine ingestion does appear capable of increasing the number of repetitions to failure in exercises such as the leg press, bench press, and leg extension.  That being said, completing more repetitions during exercise may be of interest to bodybuilders or physique competitors who often use high-volume strength training to induce muscle hypertrophy.

Research on anaerobic power output and caffeine is also inconclusive, but evidence suggests that in activities lasting at least 60 seconds, caffeine can provide an ergogenic effect.  Most studies looking at high-intensity, short duration efforts (such as repeated sprints or 30s Wingate tests) have found either improvements or no effect, but none have shown any negative effects.

What About Weight Loss?

Weight-class athletes, bodybuilders, and physique competitors may periodically use caffeine-containing products in addition to calorie restriction as a means of weight loss prior to competition. Caffeine is considered a thermogenic (“heat producing”) substance and is known to increase metabolic rate (calories burned) and fat oxidation following acute ingestion.  Weight loss products often combine caffeine anhydrous with other caffeine sources, such as green tea extract, guarana, yerba mate, and kola nut to increase metabolic rate and lipolysis, the breakdown of fat for energy.  Although caffeine has been shown to induce a thermic effect acutely (resulting in more calories burned), chronic studies on weight loss with caffeine have failed to indicate sustained benefits for long-term weight loss or maintenance, likely as a result of caffeine habituation.  So, for contest prep or athletes attempting to make weight, a cyclic approach to caffeine-mediated weight loss may be more appropriate.

Who Should/Should Not Take Caffeine?

Both recreational and competitive athletes stand to benefit from caffeine supplementation prior to exercise; however, little evidence exists to support caffeine supplementation for ergogenic effects in untrained individuals.  While trained men and women seem more likely to benefit from caffeine ingestion, there are so-called “responders” and “non-responders,” a factor which is genetically determined and will ultimately influence individual responses to supplementation.  Habitual and non-habitual caffeine users respond well to supplementation, however for an enhanced ergogenic effect, caffeine abstinence for 1-4 days (or more) has been shown to re-sensitize habituated users to caffeine’s effects. Those looking to lose weight may initially see results from using products containing caffeine, but other long-term strategies, including diet modification and exercise, should be employed to maintain weight loss.  Non-habituated users with hypertension should avoid caffeinated products since it can acutely increase blood pressure in these individuals.  Patients with cardiovascular disease, glaucoma, and women who are nursing or pregnant should not start taking caffeine products without first consulting their primary care physician.

Side Effects

Despite popular belief, current research does not support the notion of caffeine-induced dehydration during exercise, or any change in fluid balance that could be detrimental to performance.  High doses of caffeine (≥ 9 mg/kg body weight) have been associated with increased anxiety, palpitations, restlessness, headache, difficulty sleeping, and gastrointestinal distress, particularly in non-habituated users.  Long-term caffeine use results in habituation, meaning you need more to get the same effects, and increased tolerance to caffeine can develop in as little as 3 days.  Caffeine toxicity is extremely rare, due to the amount that would be required to reach lethal limits in the blood (5-10 grams, or roughly the equivalent of drinking 75 cups of strong brewed coffee over a short time period).


According to the International Society of Sports Nutrition guidelines, caffeine effectively enhances performance in trained athletes when consumed in low-to-moderate doses (~3-6 mg/kg or roughly 200-400 mg for a 150 lb person) approximately 60 minutes before exercise, but does not result in further performance benefits when consumed in higher dosages (≥ 9 mg/kg). Additionally, for prolonged exercise sessions lasting longer than 2-3 hours, smaller additional doses of caffeine may be repeated during the exercise bout, in the amount of 1-2 mg/kg.  This amount is easily obtained in caffeinated sports gels or chews and may be preferable for endurance athletes competing in events lasting several hours. Caffeine anhydrous (usually found in capsules and pre-workout powders) exerts a greater ergogenic effect when compared to drinking caffeinated coffee, tea, or cola. Caffeine is reported to have a half-life of 2.5-10 hours (depending on the individual), meaning it takes that amount of time to break down caffeine levels in the blood to half of the initial peak concentration.  This is important to consider if you work out in the afternoon or evening, as taking caffeine late in the day may interfere with sleep for some.

Botton Line on Caffeine

Caffeine has many potential benefits for performance and body composition alike and appears to be ergogenic in most exercise situations.  Aerobic endurance performance is enhanced. Strength endurance and anaerobic power may also improve, but more research is needed in this area.  Metabolism and weight loss benefits are more evident in the short term, but long term weight loss has not been observed.  Improved concentration, increased energy, and alertness are primary reasons for caffeine consumption.  Athletes and trained individuals seem to benefit more than untrained individuals, at least as far as performance is concerned.  Side effects and adverse events are generally mild and occur more often in naive users, with dosages ≥ 9 mg/kg known to increase their incidence.  Be sure to read labels and know how much caffeine is in the products you are taking, particularly if you consume more than one type of caffeine-containing product daily (thermogenic, pre-workout, caffeinated beverages, etc.).  As with most interventions, individual results may vary.

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