Caffeine & Performance
DISCLAIMER: I realize this article is far less friendly to the layman. I did not intend for it to be so "science-y", but without deleting all the solid work, I simply added summaries at the end of each section. Future articles will not be this dry. My apologies.
Caffeine is used by 90% of the world in some form, and in the United States, 80% consume caffeine on a daily basis (1). This means that caffeine is a substance that is by no means foreign to us. However, although people have used caffeine for many benefits ranging from making drowsiness dissipate in the mornings to maintaining energy throughout the day, there may still be greater use for this highly popular compound. In gyms across the world, people use preworkout drinks to help get themselves ready for tough workout sessions, because these stimulant rich preworkouts are usually packed full of caffeine, they do help a person feel more alert and primed for an exercise bout; more importantly, however, these preworkout drinks may have more of an impact on exercise performance than we think. Not only does caffeine help raise alertness, but it may have a direct impact to gym performance.
We will explore the science behind caffeine’s impact on resistance training and aerobic training.
Let’s start off running: there is still a good amount of confusion over if caffeine has a noticeable impact on resistance training, but breaking down some of the main categories, let’s examine the research.
There are few studies that have actually studied torque, but among the few that have, a statistical difference was identified in those who were treated with caffeine (7mg/kg) compared to those in the placebo group (3). So, it is probable that torque increases some with caffeine ingestion.
Repetitions Lifted/Rating of Perceived Exertion
In one double blind study trained, regular (every day) caffeine users were given 6mg/kg and compared against a placebo group. In this study, caffeine did have limited impact on performance. No upper body exercises saw any improvement between participant groups (treated vs. placebo); however, leg exercises saw a statistically significant increase (7.2%) in 67% of caffeine treated participants. (2)
This study was conducted quite well and it does show small improvements to certain lower body exercise performance, but need I remind that the small increase in performance was only found in 2/3 of the participants. Interestingly, the study did offer an explanation. Those that saw an increase in leg performance were all heavy, regular caffeine users (relative to >225mg/day) compared to the lighter, regular users (relative <150mg/day). Other studies have also found improvements in leg exercises, but no significant improvements in upper body exercises (6).
This is the most comprehensive and well controlled study and while there are a few others researching in this area, there are many variables unaccounted for in most other studies; for example, one study combined caffeine with creatine, branched chain amino acids, taurine, and glucuronolactone (4). As the comparative group was not fed the same dose of all these substances sans caffeine, it muddies the results to unusable in a caffeine analysis.
However, some other variables to consider such as Rating of Perceived Exertion (RPE) and Perceived Pain Intensity (PPI) help show some other possible benefits. Caffeine (6mg/kg) seems to have no significant effect on PPI, but does have a relative impact on RPE (similar RPE by scale, but caffeine has more repetitions per set, so per repetition, caffeine treated had less perceived exertion) during exercise than 10mg/kg of aspirin (5). In regards to total repetitions, this particular study seems to suggest repetitions increase slightly with caffeine intake, but only saw this effect in the first set, not in following sets (5). Other studies comparing RPE and repetition count found similar results when compared to placebo (6).
1 Repetition Maximum (1RM)
According to several studies, caffeine does have an impact on 1RM related testing (7)(8). One study found no significant increase in volume repetition work, but did find a statistically significance (2.1% increase) in 1RM testing on the bench press (8). Other studies observed similar results (<1kg difference between caffeine treated and placebo group) in bench press 1RM testing with a 6mg/kg treatment group (9). So, all in all, it seems caffeine does have an impact on maximum anaerobic output, but that statistical significance applied to “real world” conditions is quite small (a few kg, at best).
Another critical note is the amount of caffeine needed to elicit benefits from consumption. Most studies reviewed saw increases in performance (in analyzed variables: 1RM, RPE, PPI, and repetition) at or above 6mg/kg. Studies conducted with lighter caffeine quantities (2.5mg/kg and total 110mg, respectively), showing significant results, tend to be skewed due to their intake being compounded with other substances (4)(11).
The research is not altogether strong. Although several studies show caffeine having an impact on performance, that impact may be quite small in real world application. Caffeine impact changes from exercise to exercise as upper body 1RM testing tends to show slight improvements while lower body shows no improvements. On the other hand, caffeine may have impact on repetition work in lower body exercises, but not upper body exercises. In areas such as RPE and PPI, caffeine seems to have a small benefit. There are several theories (athletes responding differently, caffeine dosage, and habitual caffeine use) as to why caffeine has a strange effect from exercise to exercise and measure to measure, but none have been substantiated, yet (10). Finally, certain studies approached the question while looking at energy/nutritive drinks which includes other substances (Taurine, amino acids, etc) along with caffeine which may garner similar results at a lower caffeine amount than strictly caffeine ingestion.
So, in the simplest, fairest statement on caffeine impact during resistance training, we can acknowledge that caffeine has a tiny impact on performance as a whole. That impact, already minimal, may be negated by people’s sensitivity to caffeine (queasiness, anxiety, etc) as all studies controlled for hyper sensitivity. Will caffeine make any significant impact in the gym, however? Unlikely.
Does it work?
6mg/kg or higher seem to be consistently standard doses for success at optimizing caffeine impact.
In this particular area, there has been quite a number of studies, so the research is considerably more conclusive.
In one study that looked at swimmers that were required to swim 1500 meters saw a significant improvement (~30 second) in performance in those that ingested caffeine compared to those who did not (12). Other studies looked at continuous exercise intensity to exhaustion and found an increase in performance (able to sustain said intensity for longer duration of time) of almost 20% with those that were treated with caffeine over the ones that were not given caffeine (13)(14)(16). Even in trials that compared glucose to caffeine found a 7.4% increase in performance (15).
Rating of Perceived Exertion
Studies that saw improvement in performance also saw improvement in rating of perceived exertion, as well (12)(13)(16).
There is a lot of research out claiming that caffeine has a profound influence on almost every aspect of aerobic training. Not much to say except there will be a significant increase in performance with adequate caffeine intake. The postulated reason behind this is that caffeine decreases glycogenolysis and at the same time increases free fatty acid oxidation so that glycogen lasts longer while lipolysis occurs at a greater rate to accommodate this down regulation in glycogen substrate use.
Does it work?
Absolutely – without a doubt.
Again, many studies stick to 6mg/kg, so the dose is the same as for resistance training.
Caffeine, if it has any, has a small impact in resistance training performance that is more evident in repetition number and perceived exertion than in actual muscle power increases. However, caffeine has a substantial impact on endurance exercise and leads to significant increases in performance, as well as reduced perceived exertion.
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