Coffee, tea, chocolate, coca cola, what do all of these things have in common?…caffeine. For a large majority of us, we can’t start the day without it. We rely on it (maybe a little too much) to provide a morning jolt of energy or lift us out of an afternoon slump. Many athletes also turn to it in hopes of boosting their performance.

Caffeine has been studied as an ergogenic aid for decades, and for endurance athletes in particular, it is the most widely used stimulant. My husband recently published an evidence based review in the International Journal of Sport Nutrition and Exercise Metabolism entitled, “The Effects of Preexercise Caffeinated Coffee Ingestion on Endurance Performance”, which has been featured in the local newspapers, as well as the LA Times, Runner’s World, and on the international news. I don’t write all of that to boast about my husband (well maybe a little), but to say that recently I have received much education on the subject of caffeine and exercise performance and in turn would love to share the knowledge with you. So will your morning cup of joe or afternoon tea enhance the outcome of your workout? Over the next several paragraphs, I will explain how, why, and in what dosage caffeine effects performance.

How and Why?

When caffeine is consumed it is quickly absorbed through the gastrointestinal tract, and moves through the cellular membrane and circulated to tissue (1). It is then metabolized by the liver and elevated levels can appear in the bloodstream within 15-45 min of consumption with peak concentration evident between 45min – 1 hour (1). Within 3-6 hours after consumption caffeine concentration in the blood stream is decreased by 50-75% (1).

Before diving deeper into the research and mechanisms, I would like to note that majority of research on caffeine consumption is done in relation to endurance performance, not strength/power. However, it has been demonstrated that caffeine may enhance isometric leg extension strength, as well as the time to fatigue during submaximal isometric leg extension (2).

Now to the research… Multiple mechanisms have been proposed to explain the effects of caffeine supplementation on endurance performance. In the brain, caffeine acts as an adenosine agonist. Adenosine is a nervous system depressant, therefore caffeine’s inhibitory affects promotes arousal and alertness (why we drink caffeine in the morning) which may influence exercise performance (1). In addition to its impact on the CNS, caffeine may effect substrate utilization during exercise. In particular, research findings suggest that during exercise caffeine acts to decrease reliance on glycogen utilization and increase dependence on free fatty acid mobilization, which in turn reduces time to exhaustion (1). Another possible mechanism is that caffeine increases the secretion of β-endorphins leading to a decrease in pain perception. This may athletes to push past perceived, physical limits. Because caffeine is fat soluble and quickly crosses the blood brain barrier, as well as the cellular membrane of all tissues, it is difficult to determine if its effect is greater on the central nervous system or the muscular skeletal system.


In majority of studies that saw a significant effect of caffeine on endurance performance, the dosage was quite high (3-5mg/kg which depending on body size correlates to an average of 4-8, 8oz. cups of brewed coffee) (3). There was not a signifcant difference in response between 3-5mg/kg of caffeine (3). Doses higher than 5mg/kg  are close to the amount recognized as an illegal sports performance supplement (roughly 800 milligrams or more). At high doses, caffeine may work against you, potentially causing fast breathing, high blood pressure, nervousness, an upset stomach and intestinal tract, and irritability. Therefore, using high doses of caffeine with exercise should be discouraged for individuals with high blood pressure. Caffeine has also been said to be a diuretic. However, there have been no significant findings that caffeine effects hydration during exercise (1).

What if you are a habitual caffeine user? A recent research study also found that habitual users in low dosages (<75 mg/day) build a tolerance and do not see a significant response of high dosages of caffeine to their performance (4). Therefore, in order to use caffeine as an ergogenic aid, you should refrain from habitual use and only use when needed for performance enhancement.

So while caffeine has been shown to improve endurance performance, the amount you have to consume may be difficult to take in prior to your morning run or afternoon bike ride. If you do use caffeine on a consistent basis, think about maybe abstaining for a few days prior to a big competition and using the day of a race.

By: Lauren Higgins, M.S., CSCS, FMS-level 1

SPARC Sports Performance Coordinator


  • Goldstein, E.R., Ziegenfuss, T., Kalman, D., Kreider, R., Campbell, B., et al. (2009). International society of sports nutrition position stand: caffeine and performance. Journal of the international society of sorts nutrition, 7(5). Retrieved from
  • Kalmar JM, Cafarelli E. (1999). Effects of caffeine on neuromuscular function. Journal of applied physiology. 87: 801-808.
  • Higgins, S. Straight, C.R., Lewis, R.D. (2016). The effect of preexercise coffee ingestion on endurance performance. International journal of sport nutrition and exercise metabolism, 26(3): 221-239.
  • Beaumont, R., Cordery, P., Funnell, M., Mears, S., James, L., et al. (2016). Chronic injestion of a low dose of caffeine induces tolerance to the performance benefits of caffeine. Journal of sports sciences, 1-8.