|With only 65mg of caffeine, an espresso provides only ~12.5% of the amount of caffeine used in the study at hand.|
One thing most of these studies have in common is that they tested the subjects' strength or power production during short workouts. Studies that investigate the effects of caffeine in higher volume contexts, on the other hand (e.g. Lang. 2015; Thomas. 2015), confirm that caffeine is rightly the most (ab-)used ergogenic among fitness enthusiasts.
One thing that has recently caught my attention on Facebook is the claim that the performance enhancing effects of caffeine put you at risk of rhabdomiolysis, i.e. the potentially dangerous breakdown of muscle tissue. In theory, it'd appear logical to assume that an agent that has repeatedly been proven to significantly lower the perceived exertion/fatigue as well as muscle pain during exercise could lead to a greater degree of muscle damage during exercise.
|Figure 1: Graphical overview of the experimental design of Ribiero's study (Ribiero. 2016).|
"All of them had at least 5 years of experience in the sport and trained for about 4 hours a day, 4-5 days a week. No athlete had a previous medical history of cardiopulmonary disease or used any medication during the study. The athletes reported intake of ~ 60 mg of caffeine per day (~ 1 cup of coffee)" (Ribiero. 2016).In a randomized, placebo-controlled, double-blind crossover study, the subjects reported to the laboratory at two occasions after an 8-h fast and at least 24h of caffeine abstinence. 60 minutes after having a standardized breakfast, which consisted of bread, white cheese, and orange juice (CHO: 87 g, 348 kcal; PTN: 13.5 g, 54 kcal; LIP: 7 g, 63 kcal; Total: 465 kcal), they consumed either placebo (PLA), or caffeine (CAF; 6mg/kg body weight) and remained seated for another 60 minutes.
But this is not resistance training! While you're absolutely right, jumping is at least as notorious for producing muscle damage as regular resistance training. It is thus unlikely that leg presses or squats would have produced a greater degree of muscle damage than this intense VJ protocol.After the 60-minute delay during which the serum caffeine levels rose to peak values (see previous SuppVersity article), they performed a short warm-up and a standardized vertical jump test the scientists describe as follows:
"The VJ performance was evaluated by the jump platform System Optical (Cefise®, São Paulo, Brazil). This equipment consists of a laptop with the software "Jump System" (version 1.0, São Paulo, Brazil), connected by a cable to a resistive (or capacitive) platform (equipped with infrared optical sensors). The timer software is triggered by the feet of the subject at the moment of release from the platform, and will be stopped at the moment of touchdown. This equipment has the same principle of “Ergojump” to inform the flight time (ms) and contact (ms).
Figure 2: Mean leg power during VJ (Ribiero. 2016).
The error of measurement, when compared with film analysis has been reported to be in the order of ± 2% (18). The athlete was positioned, barefoot, in the interior of the platform and the jumps were performed starting from a standing position until approximately at an angle of 90° knee, using help from upper limbs at the time of the VJ execution" (Ribiero. 2016).The VJ data were analyzed by average leg power (Watts/Kg) generated by the athletes. In that, the scientists separated the total number of vertical jumps into tertiles, so that they could have an understanding of the behavior of the jumps in the 1st tertile (i.e., theoretically better performance), in the 2nd tertile (i.e., theoretically an average performance), and 3rd tertile (i.e., theoretically a drop in performance).
Your muscle is not the only thing that could be overtaxed - Even though the ability to perform more sets / work out more intensely / longer may not have affected the primary marker of muscle damage in the study at hand, the chronic consumption of high doses of caffeine may still pose a risk to your central nervous system and contribute to sympathetic overtraining. Therefore I'd still recommend you stick of max. 400-600 mg caffeine per day and, instead of increasing the dosage, when it stops working, take a "caffeine break" whenever you stop noticing the "caffeine spike".This allowed Ribiero et al. to make comparisons between groups and to assess the effects of supplementation. Effects of which the data in Figure 3 tells you that they became evident only in the latter tertile of jumps:
|Figure 3: Nonlinear regression analyses (polynomial regression 3rd order). Leg of the power generated in each sets of athletes with tertiles in placebo (PLA) and caffeine (CAF) trials (Ribiero. 2016).|
At the same time, however, it lead to a highly significant increase in blood lactate levels (+42.59%) after the execution of vertical jump test (p <0.05). In contrast to what the initially discussed hypothesis would suggest, though, this increase in lactate was not accompanied by significant increases in serum CK levels of the athletes (see Figure 4).
- Lang, K., and E. B. LaFountaine. "Effects of caffeine as an ergogenic aid on weight lifting regimes in male collegiate athletes." International journal of exercise science: Conference proceedings. vol. 12. no. 1. 2015.
- Thomas, Gabrielle. Is coffee an effective pre-workout drink?–The effects of ingesting naturalistic doses of caffeine on one-repetition maximum muscular strength and muscular endurance in females. Diss. Cardiff Metropolitan University, 2015.
- Ribiero, et al. "Caffeine attenuates decreases in leg power without increased muscle damage." Journal of Strength and Conditioning Research (2016): Publish Ahead of Print | DOI: 10.1519/JSC.0000000000001332
- Trevino, Michael A., et al. "Acute Effects of Caffeine on Strength and Muscle Activation of the Elbow Flexors." The Journal of Strength & Conditioning Research 29.2 (2015): 513-520.