Research: caffeine has limited effect on muscle strength

Caffeine can increase maximal strength. The size of this effect appears to differ between large and small muscle groups. However, research shows different results on both points. Recent research conducted at the University of Edinburgh seeks to provide clarity. This seems to better demonstrate the strength-increasing effect of caffeine. Overall, however, the effect appears to be much smaller than that of creatine. Since caffeine can counteract the effect of creatine, creatine is the better choice when it comes to increasing muscle strength.

Caffeine for increased muscle strength?

Recent research has emerged on the influence of caffeine on maximal strength and explosive strength [1].

Regarding endurance and fatigue, it is clear that caffeine offers benefits [2,3]. Also, when it comes to longer sprints (running or cycling, for example) [4,5]. As long as it involves efforts longer than a minute, caffeine can provide an advantage.

However, when it comes to maximal strength, the situation is less clear. Several studies have been conducted in this area, with sometimes conflicting results [6,7,8,9]. Nevertheless, in practice, caffeine is used more by strength athletes than by other athletes [10]. There are several reasons to question whether this is justified.

The recent research conducted at the University of Edinburgh aims to shed light on this.

Effect of caffeine: location and size of muscle groups?

Previous research showed differences in the effect of caffeine on (maximal) strength between the upper and lower body. Some studies showed an effect of caffeine on the strength of upper body muscles but not lower body muscles [11,4]. For example, American researchers observed in 2006 that ingestion of 201mg of caffeine increased maximal strength (expressed as the “1RM,” the weight with which one repetition could be done) in bench press but not in leg extensions [11].

Other studies showed the opposite [12,13]. Such as research from the California State University in 2011 [12]. When training with a weight of 70-80 percent of the 1RM, more repetitions could be performed on the leg press, but there was no difference in the shoulder press and bench press. In this case, 6mg per kilogram of body weight of caffeine was ingested, more than double the amount in the previously mentioned study.

Additionally, there are studies that saw no effect at all, neither on the lower body nor the upper body [14,15]. For example, the same researchers from the California State University. They observed in another study three years earlier no effect of the same amount of caffeine on both lower body and upper body when looking at the 1RM [14]. So, caffeine did not increase the maximum weight they could lift for one repetition.

In a systematic review from Georgia State University on the effects of caffeine, 27 studies on the effects of caffeine on maximal strength were compared [16]. The overall outcome was that maximal strength increased by 4%. It was noticed that the researchers conducting the review observed that the size of the muscle groups trained and their location influenced this effect. This was not observed in the effect of caffeine on endurance. The review found that caffeine had a greater effect on larger muscle groups than smaller muscle groups and a greater effect on the lower body compared to the upper body. The difference between lower and upper body can be explained by the fact that the muscle groups of the lower body are larger.

Activation of muscle fibers

As an explanation (for this difference between the effect on small and large muscle groups), the researchers from Georgia State University look at the percentage of muscle fibers activated during exertion for maximal strength. They refer to previous research showing that fewer muscle fibers are simultaneously activated in large muscle groups. For example, the quadriceps activate 80-95 percent of muscle fibers while in smaller muscle groups like the calf muscles, it’s 90-99 percent [17].

Caffeine seems to mainly exert its influence via the central nervous system and to a lesser extent in the muscles themselves. Simply put, it improves the software, not the hardware. The improved control from the brain by caffeine leads to activation of more muscle fibers. If a large part of the muscle fibers is already activated, as in small muscle groups, there is less room for improvement than when fewer muscle fibers were activated. This explanation doesn’t fully explain the difference between upper and lower body. The researchers argue that the muscle groups of the lower body are generally larger, which is correct. It’s just strange that, for example, no improvement was seen in the hamstrings. Moreover, this is a systematic review comparing various studies. There was no comparison between the effect on different muscle groups of the same person, but comparisons were made between different individuals under different conditions (participant’s level of training, diet, type of training, gender, etc.).

Recent research at the University of Edinburgh

Based on the limitations of the systemic review from Georgia State, the researchers from Edinburgh wanted to address the gaps with their recently published research.

Sixteen trained men (at least one year of training, twice a week) with an average age of 21 participated in the study. They had to indicate beforehand how much caffeine they normally consumed. Those who consumed more than 300mg per day were not allowed to participate because this could affect one of the ways caffeine may work. 24 hours before, they were not allowed to consume caffeine-containing products, alcohol, or engage in heavy training.

The participants had to follow the approximately one-hour protocol on two different days. They received a solution with 6mg of caffeine per kilogram of body weight or a placebo. This would be sufficient to maximize the amount of caffeine in the blood [18]. The following week, the men who had previously received a placebo were given caffeine, and vice versa. Fifteen minutes after taking the caffeine/placebo, they did a 15-minute warm-up. 30 minutes after ingestion, testing of maximal strength began.

Maximal strength was tested in two muscle groups of the upper body and two muscle groups of the lower body. Four exercises were performed: for the biceps and forearms, as well as quadriceps and calves. The highest of three attempts at maximal strength was recorded. A week later, the same protocol was followed, but with ingestion of the other solution (placebo instead of caffeine or vice versa).

Results

Firstly, an effect of caffeine on peak power was observed. When looking at the effect on large and small muscle groups, they saw a difference that was just not large enough to be statistically significant (p = 0.056). The increase in peak power was greater as the muscle group size increased. There was a “moderate” effect on the quadriceps and a “small to moderate” effect on the calves, forearm muscles, and biceps.

A major finding of the present study is that acute caffeine supplementation (6 mg/kg) appears to enhance MVC strength, as demonstrated by the significant (p = 0.011) increase in mean isokinetic peak torque in upper and lower body muscle groups.

…The current results indicate that a moderate dose of caffeine (6 mg/kg), consumed approximately 30 minutes before performance, improves MVC strength in upper and lower body muscle groups, in resistance-trained men. This research may be useful for competitive and recreational athletes aiming to increase strength-power performance. Further investigation is required to verify the effect of muscle group size.

-T.D. Timmins, University of Edinburgh

*MVC=Maximum Voluntary Contractile

Conclusion: Still, choose creatine for more muscle strength?

As the researchers themselves indicate, more research needs to be done to identify the various conditions that can lead to different results. For example, consider the amount of coffee participants typically drink. In an article about caffeine as a fat burner, I wrote that it has been found that people who consume more than 300mg of caffeine per day no longer have a fat-burning effect from caffeine [19]. This may also apply to the effect on muscle strength [20].

A more important question, however, is whether caffeine is worth it in terms of maximal muscle strength. Especially when compared to creatine. I recently wrote an article about the effect of caffeine on the action of creatine. It showed that the intake of 3.5 to 5 cups of coffee per day negates the effect of creatine [21]. The advice was therefore to choose creatine if muscle strength or muscle mass was your main goal instead of, for example, fat burning and endurance.

Since the effect of creatine on muscle strength and mass is greater than that of caffeine [22], I would not recommend caffeine supplementation as it comes at the expense of the greater effect of creatine.

References

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