“Caffeine, in small and repeated doses, about sixty centigrams per day, which may be prescribed with advantage to soldiers on the march, facilitates muscular work in augmenting the activity, not directly of the muscle itself, but of the motor nervous system, cerebral as well as medullary”
- Anonymous, Journal of Science, 1890 (Vol 15, page 244).
This year, in 2015, caffeine will be the most widely consumed "drug" in the world, the most widely consumed CNS stimuland in the world, and the most common ergogenic aid used to enhance performance in the world. If you aren't a coffee drinker, and you think you're missing out, you're probably right. Furthermore, if you avoid caffeine for whatever reason, that must be a stressful part-time job. Caffeine is found in many products that often consumers aren't even aware of. The Table below from the article by Burke (2008) shows just a handful of examples of caffeine sources, and the shocking reality that amounts of caffeine per product can vary extensively. Even in the same sized, same brewed, same location of Starbucks, caffeine content caried by as much as 300 to 564 mg per serving. Can you imagine taking that kind of gamble with anything else? That is comparable to having a beer and instead of the 4% alcohol you were expecting, you instead consume closer to 8% alcohol, unknowingly.
Some of the newer products on the market not depicted in the table above include caffeinated mints and gum, Energy drinks, shots and gels for athletic performance, Lipbalms or edible sprays, Snortable caffeine sticks, caffeine patches, and caffeine pills! Personally, I'll stick to my warm caffeinated coffee.
Some myths about coffee include:
1) Increase free fatty acid oxidation (thought to improve weight loss)
2) Sparing of muscle glycogen (for better endurance performance)
3) Increased bowel movements
The above are indeed myths, and will be saved for another blog post, but let's move onto the endurance benefits that are claimed to come from caffeine.
Firstly, it is clear that the caffeine acts on Ryanodine receptors, small "gates" at the microscopic level of the muscle fiber, that release calcium in order for a muscle contraction to occur. Secondly, caffeine acts on "adenosine receptor antagonism" (Tarnopolsky, 1994). Adenosine plays an important role in biochemical processes, such as energy transfer. This phenomenon occurs because adenosine and caffeine are structurally similar, so, in a way, caffeine tricks the body into doing the opposite of sleep. Thirdly, caffeine acts on sodium potassium pumps, preventing depolarization action potential block, which contributes to fatigue during exercise.
In a review of caffeine and endurance performance by Ganio (2009), it was recommended that athletes take up to 6mg/kg body weight for optimal performance enhancement. The review recognized that timing of ingestion mattered, and despite the discrepancies in the times of ingestions among the studies included in the review, the recommendation given was to consume caffeine between 30 minutes to 2 hours prior to competition for optimal results. The mode of ingestion did matter, and caffeine pills were found to be more affective than drinks or other products containing caffeine, probably due to their variable content of caffeine. Finally, it was best to obstain from caffeine at least 7 days prior to the competition if the athlete is a habitual caffeine drinker - as this increased the effect of the dose.
Dose should be individualized for each athlete, and consumption of caffeine pills should never be tested on race day - but instead tested through trial and error prior to the athlete's race. A dose of 2-5mg/kg has been shown to increase performance by 3% on average, with minimal gastric upset (keeping in mind that there are responders and non-responders to caffeine based on habituation). Doses of >5mg/kg have been shown to increase performance on average by 7%, but again, outliers do exist. One thing is clear in the literature, which is that there are no futher increases in performance after 9mg/kg consumption of caffeine, and this size of a dose can be associated with side effects such as jitteriness, GI upset, headaches, tachycardia and nausea (Shearer & Graham, 2014).
So to conclude this blog post and to quote a great, yet anonymous author: "I don't have a problem with caffeine. I have a problem without caffeine."
Drink responsibly, and often.
Anonymous. (1890). Action of Caffeine. Journal of Science, 15(376), 244.
Bell, D. G., Jacobs, I., & Zamecnik, J. (1998). Effects of caffeine, ephedrine and their combination on time to exhaustion during high-intensity exercise. European Journal of Applied Physiology and Occupational Physiology, 77(1998), 427–433. doi:10.1007/s004210050355
Burke, L. M. (2008). Caffeine and sports performance. Applied Physiology, Nutrition, and Metabolism = Physiologie Appliquée, Nutrition et Métabolisme, 33(6), 1319–34. doi:10.1139/H08-130
Ganio, M. S., Klau, J. F., Casa, D. J., Armstrong, L. E., Maresh, C. M. (2009). Effect of Caffeine on Sport-Specific Endurance Performance: A Systematic Review. Journal of Strength and Conditioning Research, 23(1), 315–324.
Goldstein, E. R., Ziegenfuss, T., Kalman, D., Kreider, R., Campbell, B., Wilborn, C., … Antonio, J. (2010). International society of sports nutrition position stand: caffeine and performance. Journal of the International Society of Sports Nutrition, 7(1), 5. doi:10.1186/1550-2783-7-5
Harland, B. F. (2000). Caffeine and nutrition. Nutrition, 16(7-8), 522–526. doi:10.1016/S0899-9007(00)00369-5
MacIntosh, B. R., & Wright, B. M. (1995). Caffeine ingestion and performance of a 1,500-metre swim. Canadian Journal of Applied Physiology = Revue Canadienne de Physiologie Appliquee, 20(2), 168–177. doi:10.1139/h95-012
Robertson, D., Wade, D., Workman, R., Woosley, R. L., & Oates, J. a. (1981). Tolerance to the humoral and hemodynamic effects of caffeine in man. Journal of Clinical Investigation, 67(4), 1111–1117. doi:10.1172/JCI110124
Shearer, J. (2014). Methodological and metabolic considerations in the study of caffeine-containing energy drinks. Nutrition Reviews, 72, 137–145. doi:10.1111/nure.12131
Shearer, J., & Graham, T. E. (2014). Performance effects and metabolic consequences of caffeine and caffeinated energy drink consumption on glucose disposal. Nutrition Reviews, 72 Suppl 1, 121–136. doi:10.1111/nure.12124
Tarnopolsky, M. a. (1994). Caffeine and Endurance Performance. Sports Medicine, 18(2), 109–125. doi:10.2165/00007256-199418020-00004
Zhang, Y., Coca, A., Casa, D. J., Antonio, J., Green, J. M., & Bishop, P. a. (2014). Caffeine and diuresis during rest and exercise: A meta-analysis. Journal of Science and Medicine in Sport / Sports Medicine Australia. doi:10.1016/j.jsams.2014.07.017