Published in Nutrients, the research found that anhydrous caffeine (the powdered form, commonly used in pre-workout supplements) does not positively affect muscular endurance exercises. In fact, it had a negative effect on one performance parameter: the number of sit-up repetitions.
However, the researchers from the universities of Thrace, Thessaloniki and Athens, Greece, said their results suggest that caffeine may have benefits for athletes rather than physically active individuals.
“Caffeine supplementation may have different effects depending on the individual training level,” they wrote. “The participants in the present study were mainly active individuals, with only two being competitive CrossFit athletes. Indeed, these two athletes performed more repetitions after consuming caffeine than the placebo.”
Caffeine as an ergogenic aid
Established in 2000, CrossFit is a form of high-intensity training that includes varied functional movements, combining the elements of weightlifting, gymnastics and aerobic exercise.
Supplements are popular among CrossFit athletes, with one study finding that most participants (82.2%) consumed at least one supplement, with roughly one in five (20.7%) consuming pre-workout or energy drinks.
However, while a number of studies have shown that caffeine can improve exercise performance, the results have not been conclusive. Indeed, a recent critical evaluation of the literature by the International Society of Sports Nutrition (ISSN) found that supplementation with caffeine has been shown to acutely enhance various aspects of exercise performance in many but not all studies.
When looking specifically at CrossFit, there is limited evidence supporting the use of caffeine as an ergogenic aid. Four randomized, double-blind, crossover studies showed that caffeine does not improve CrossFit performance, while another found that a medium dose (6 mg) can induce improvements in exercise repetitions and reaction time.
Given this varied evidence, the researchers set out to examine the effects of a relatively high dose of caffeine (7 mg/kg body mass) on performance and physiological responses to a demanding CrossFit workout.
Study details
In the study, 12 male cross fit athletes performed two CrossFit training sessions seven days apart. In the first, the participants received 7 mg/kg of anhydrous caffeine 60 minutes before exercising, and in the second, they received a placebo.
Their performance was measured using various CrossFit exercises, including push-ups, power cleans, front squats, sit-ups and deadlifts. Performance was defined as the total number of repetitions per round, as well as the number of repetitions performed in each exercise per round.
Blood lactate levels, heart rate and information about possible side effects were also recorded before and after exercise.
Overall, caffeine had no significant effect on the total number of repetitions or the number of repetitions per round in most of the exercises included in the program. The only recorded difference was a 9.5% decrease in the number of sit-up repetitions between the third and fourth rounds.
In addition, heart rate and blood lactate concentration were not affected by caffeine supplementation. However, side effects were more common with caffeine supplementation compared to placebo (67% vs. 25%), with gastrointestinal disturbances reported by one third of participants.
The researchers say these symptoms may have affected performance, since three of the eight individuals who performed fewer abdominal repetitions after caffeine intake experienced gastrointestinal discomfort.
Why do the findings differ from previous research?
The researchers noted various factors that could explain the results of their study and why they diverge from previous research on caffeine consumption pre-exercise.
“According to a meta-analysis, caffeine improves muscular endurance by 6–7% when large muscle groups are engaged through repetitions to exhaustion in multiple sets of weightlifting, with fewer than 30 repetitions, a number not comparable to the total repetitions performed in CrossFit programs like the one in the present study,” they wrote.
“Additionally, even for the number of repetitions of each exercise per round, the results are not comparable, as in our training program, there were insufficient rest intervals, unlike the studies used in the meta-analysis, which also typically involved only isolated exercises and muscle groups.”
Habitual caffeine consumption may have also played a role, the researchers added. However, they believe this is unlikely given that the amount of caffeine administered during the trial was at a much higher dose compared to the participants’ typical intake.
“Regular caffeine consumption seems to reduce the ergogenic effects of acute intake, possibly by altering physiological responses due to increased adenosine receptors,” they wrote. “However, there is evidence that if the dose administered before exercise is higher than the usual daily intake, caffeine still exerts ergogenic effects.”
Given the small sample size and the inclusion of only male participants, the researchers say more research is needed to truly understand the potential for caffeine to boost exercise performance.
“Further randomized studies with larger sample sizes are needed to minimize limitations and examine the factors affecting the physiological responses and performance changes following caffeine supplementation in different individuals,” they concluded.
Source: Nutrients. doi: 10.3390/nu17091419. “Effects of an Acute High Dose of Caffeine on Physiological Responses and Performance During a Strength-Focused CrossFit® Workout: A Randomized, Double-Blind, Crossover Study”. Authors: Z. Konidari, et al.
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