Wednesday, May 17, 2017

Coffee Never Disappoints: Myth that Habitual Consumption Reduces Caffeine's Acute Ergogenic Effects... Dispelled!?

I must remind you, though, that performance benefits in one domain don't always transfer to another one. In other words: While the study seems to dispell the myth for classic endurance training, effects on activities where CNS activity is more important, like lifting, for example, may still be impaired w/ habitual intake.
I guess even I have to confess that I may have propagated the myth that habitual caffeine consumers would not benefit to the same extent from pre-workout caffeine supplementation as caffeine naive individuals. What I know for a fact, though, is that I also mentioned in previous caffeine/coffee articles that the "jitters" caffeine-naive individuals may experience could ruin all the benefits of the often-heard of extra effect on the central nervous system (CNS).

As de Souza Gonçalves et al. (2017) point out in their recent study, previous experimental efforts to determine "the relationship between habitual intake of caffeine and the effect of caffeine supplementation on exercise performance are inconsistent" (de Souza Gonçalves 2017).
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Dodd, et al. (1991), for example, observed no differences in the effects of caffeine on exercise performance between caffeine naïve individuals and habitual consumers. Conversely, Bell & McLellan (2002) demonstrated that non-habitual caffeine consumers cycled longer than habitual consumers during a cycling-to-exhaustion protocol at 80% VO2max following acute caffeine ingestion. Potential reasons for the different outcomes are, according to de Souza Gonçalves, ...
  • the binary stratification of subjects as habitual (> 300 mg/day) or non-habitual consumers (< 50 mg/day) that disregards the potential relevance of intermediary intakes,
  • the low total number of subjects (n < 21), which hampers definitive conclusions
  • the use of time-to-exhaustion tests to assess performance, a method, which has been subjected to criticisms due to poor external validity and large variability
Reason enough for the scientists from the University of Sao Paulo to (re-)investigate whether the long-standing notion holds true that habitual intake of caffeine (i.e., low, moderate, and high) influences the effects of acute caffeine supplementation on exercise performance using a large sample of volunteers and a reliable endurance exercise protocol. As the scientists point out, they ...
"[...] hypothesized that habitual caffeine intake would influence the ergogenic effects of caffeine supplementation, with greater aerobic exercise performance gains in individuals with lower regular consumption" (de Souza Gonçalves 2017).
In other words: de Souza Gonçalves believed that the myth was true. Their analysis of the data they collected in their double-blind, crossover, counterbalanced study with forty male endurance-trained cyclists who were allocated into tertiles according to their daily caffeine intake: low 30 (58 ± 29 mg/d), moderate (143 ± 25 mg/d), and high consumers (351 ± 139 mg/d), however, dispels the myth that habitual caffeine consumption would reduce the ergogenic effects of the world's #1 stimulant significantly.
Figure 1: Time-trial performance in caffeine (CAF), placebo (PLA) or no supplement (CON) according to habitual caffeine intake ((P > 0.05) - low (58±29 mg/d), moderate (143±25 mg/d), and high consumers (351±139 mg/d  | de Souza 2017).
As the data in Figure 1 already suggests, the scientists' mixed-model analysis revealed that their subjects' time-trial performance on 6mg/kg caffeine was significantly improved compared to both the placebo and the control trial (29.92±2.18 min vs 30.81±2.67 and 31.14±2.71 min; P = <0.0002).

More importantly, however, their analysis of covariances (ANCOVA) revealed no influence of habitual caffeine intake as a covariate on exercise performance (P=0.47). Neither was there a sign. difference between tertiles of caffeine intake (P=0.75), or a correlation between habitual caffeine intake and absolute changes (CAF – CON) in time-trial performance with caffeine (P=0.524).
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But it doesn't work for me! If you're now asking yourselves why caffeine doesn't work for you, then, I have to say that genetics appear to play an important role, here, as well. With the scientists' individual analysis showing that eight, seven and five individuals improved above the variation of the test in CAF in the low, moderate and high tertiles, respectively, there's at least little doubt that you can/should blame your habitual caffeine intake for that - after, all even the Fisher's Exact Test did not show any significant differences in the number of individuals who improved in CAF between the tertiles of caffeine intake (P>0.05). So, what? Myth busted!? Well, at least for time-trial performance, in the gym, things may still look different | Comment!
References:
  • Bell, Douglas G., and Tom M. McLellan. "Exercise endurance 1, 3, and 6 h after caffeine ingestion in caffeine users and nonusers." Journal of Applied Physiology 93.4 (2002): 1227-1234.
  • de Souza Gonçalves, L., et al. "Dispelling the myth that habitual caffeine consumption influences the performance response to acute caffeine supplementation." J Appl Physiol (2017) - Article in press as of May 11.
  • Dodd, S. L., et al. "The effects of caffeine on graded exercise performance in caffeine naive versus habituated subjects." European journal of applied physiology and occupational physiology 62.6 (1991): 424-429.