Scientific Review Series: Caffeine Supplementation and Exercise Performance

Scientific Review Series:
Caffeine Supplementation and Exercise Performance

Published March 29, 2019 in British Journal of Sports Medicine

Our goal with our scientific review series is to break down studies related to supplements, health, athletic performance, and general wellness. Often times, these scientific studies can be a little dry and difficult to get through. We've taken the liberty to cut through all the "science-talk" and deliver to you a simple and straightforward break down of these studies!

Today, we're reviewing a study titled: "Wake up and smell the coffee: caffeine supplementation and exercise performance—an umbrella review of 21 published meta-analyses"

This study looked at one of the most basic and widely used ingredients in pre-workout supplements: caffeine. It's generally agreed upon that a hefty dose of caffeine will improve your workout. This study wanted to reevaluate and update the effects of caffeine on athletic performance. Every once in awhile, it's useful to review all the new studies that have come out and see if there's any new connections or finding.

Summary

Objective: To review and summarize findings of published studies that have examined the effects of caffeine on exercise performance.

Study Design: Twelve databases were searched and 405 studies relating to caffeine and exercise performance were evaluated. These results were then combined and analyzed.

Results: Caffeine supplementation improved aerobic endurance, muscle strength, muscle endurance, anaerobic power, vertical jump height, exercise speed, and short-term high-intensity exercise. 
 

    Background

    Caffeine is a supplement that has a long history of use for improving athletic performance. Caffeine is used by both amateurs and professionals around the world. In fact, after the World Anti-Doing Agency removed caffeine from it's list in 2004, a whopping 74% of urine samples collected contained caffeine! 

    Given the widespread use of caffeine, many research groups have tried to scientifically evaluate the effects of caffeine on the body. One of the struggles of doing such research is that the human body is very unique and different people react differently to supplements. As a result, scientists have turned to meta-analysis. Meta-analysis is the process of combining multiple sources of data and using it to identity common effects or trends. 

    This study combed through hundreds of research studies involving caffeine and athletic performance and evaulated the data to determine if there was sufficient evidence for the effects of caffeine.

    Study Design

    The research group searched through 12 scientific review databases for studies that involved caffeine and physical performance. There were 405 studies that were found and evaluated.

    The criteria used to evaluate if a study could be included in the analysis were:

    • Participants  - Study subjects had to be healthy individuals of both sexes and all ages
    • Interventions - Studies had to examine the effect of caffeine only on exercise performance. Studies that looked at caffeine + other ingredients were not included. For example, a study looking at sports energy drinks is not included because the energy drink has caffeine along with other ingredients, so the effects could not be isolated to caffeine alone. 
    • Comparison Group- Studies had to have a placebo group, meaning a group of participants who did not take any caffeine so you can compare results with caffeine vs without caffeine.
    • Outcome Measures- Studies had to look at the effect of caffeine on exercise performance specifically. For example, studies that looked at cognitive effects like awakeness were not included.
    • Methodology Quality Evaluation- Studies were evaluated on their methodology, or how they carried out their study. Research studies have to be carefully controlled so that the outcome can be measured. You do not want wrong data because you collected data the wrong way. You also do not want any sort of bias in collecting the results. This evaluation was based on the AMSTAR 2 Checklist  Full AMSTAR 2 Checklist Link.
    • Results Quality Evaluation- Studies were also evaluated on the accurately of their results. After collecting the data, you need to evaluate if the data is meaningful or if no conclusion on can be drawn. The results summary was based on the GRADE checklist. Full GRADE Checklist Link.

    Of the 405 studies, only 11 of them qualified in this meta-analysis!

    From these 11 studies, the research group combined the data and looked at a variety of performance metrics including: maximal running/cycling/rowing speed, aerobic endurance, peak and mean power, 1 Rep Max strength, muscular endurance, and maximal voluntary strength. 

    Results

    The results for the study show that caffeine has performance enhancing effects on muscle endurance, muscle strength, anaerobic power and aerobic endurance!

    The below graph shows the results of different athletic performance measures vs study participants who took a placebo (no caffeine) and those who did take caffeine. The black bars indicate the confidence of the result measured in a specific study, and the grey lines indicate the measure of confident if the result was applied to future studies. The effects we are most confident in are where the black and grey lines both fall in the "Favors Caffeine" section.


    What's interesting is that these studies indicate that caffeine is potentially more effective at increasing aerobic exercise over muscle strength and endurance. This means that taking caffeine could be more beneficial for longer distance running, cycling, rowing, etc.

    Additional results from the study included:

  • Optimal Dose of Caffeine - Most commonly used dosage from scientific studies is 3mg/lb but the optimal dose of caffeine is not conclusive. More dose-response studies are needed to be done that account for various factors such as exercise type, muscle action type, and individual response. 
  • Is coffee a good way to consume caffeine?  - Coffee may be used as a source of caffeine, but it may not be the most practical form of caffeine. A majority of studies used caffeine powder because it is more practical to take vs 2-4 cups of coffee.
  • Conclusion

  • Of the 11 included reviews, all report significant improvements in at least one component of exercise performance following caffeine ingestion with the effect size magnitude ranging from small to moderate.
  • The effect sizes for meta-analyses that focused on aerobic tests of performance are generally higher than those that used anaerobic tests of performance.
  • Additional questions the researchers wanted future studies to look into:

  • The effects of caffeine habituation - Is there a reduction in effectiveness of caffeine after repeated short term use?
  • Optimal timing of caffeine ingestion - is there a "best time" for consuming caffeine before exercise? 
  • Effects of different sources of caffeine - Does the source of caffeine have an effect on athletic performance?
  • Effects of caffeine among trained versus untrained individuals - Do untrained and trained individuals respond better/worse to caffeine?
  • Chronic effects of caffeine on exercise adaptations - Use the long term use of caffeine result in long term improvement in athletic performance?

  • Reference for Full Study: 

    Grgic J, Grgic I, Pickering C, et al Wake up and smell the coffee: caffeine supplementation and exercise performance—an umbrella review of 21 published meta-analyses Br J Sports Med Published Online First: 29 March 2019. doi: 10.1136/bjsports-2018-100278

    Link for Full Study