Researchers in Brazil and the United States examined whether caffeine (5 mg/kg body mass) improved maximal strength and muscular endurance in trained young men and explored individual differences in responses to caffeine and placebo effects.
They hypothesized that both caffeine ingestion and the expectation of consuming caffeine would improve performance.
Separating caffeine effects from placebo in athletic performance
Athletes commonly use caffeine to enhance performance and it has been shown to improve endurance and potentially slightly increase maximal strength and muscular endurance.
However, research findings vary, with some studies reporting performance improvements while others find no effect.
This could be due to inconsistent testing methods and participant variations or the placebo effect, where positive expectations about a substance improve performance even when the substance itself has no active effect.
In caffeine studies, participants frequently recognize when they have consumed caffeine due to its noticeable effects, which can influence their behavior. If athletes believe they did not receive caffeine, they can perform worse in placebo trials, artificially exaggerating caffeine’s apparent benefits.
Therefore, the researchers of the new study, published in Nutrients, noted that research needs experimental approaches to separate caffeine’s physiological effects from expectancy effects.
Caffeine effects on muscle performance
Researchers recruited 16 physically active men aged 18–30 to participate in the study consisting of six sessions. The first session collected demographic data, anthropometrics and familiarized participants with the procedures, and the second session confirmed strength measurements and familiarized participants with the testing protocols. The remaining four sessions were randomized experimental trials.
In each experimental session, participants received either caffeine (5 mg/kg body mass) or a placebo, while researchers told them either that they received caffeine or a placebo. This created four conditions: Told caffeine and received caffeine (C/C), told placebo and received caffeine (P/C), told caffeine and received placebo (C/P), and told placebo and received placebo (P/P). Participants ingested capsules one hour before testing.
Participants completed a perceived recovery status quiz at each session and a caffeine side-effects questionnaire every 15 minutes after supplementation. Researchers measured body mass, height, and body composition, and assessed muscle strength and muscular endurance through sets of squat repetitions.
Researchers also measured blood lactate before testing and at two, four and six minutes after the endurance test using capillary blood samples.
Results showed that caffeine intake significantly increased peak torque and maximum work, but the effects were small and mainly occurred at static and slower contraction speeds. The placebo effect did not significantly affect strength outcomes.
Caffeine did not significantly improve repetitions or total training volume during the squat endurance test. It did, however, increase post-exercise blood lactate levels, and simply expecting caffeine also produced a smaller increase, which the researchers noted was due to anticipatory nervous system responses, which may influence physiological outcomes.
Furthermore, responses to caffeine varied widely, and while many participants showed individual performance improvements, especially in strength measures, only a small proportion responded consistently across all tests. The researchers suggested that caffeine may therefore act through multiple physiological mechanisms.
The researchers noted that as caffeine responders in the maximal repetition test were not consistently responders in the strength tests, the variability in responses could not be solely attributable to central mechanisms of caffeine ergogenicity.
“In our study, these heterogeneous responses in ME were not correlated with habitual caffeine intake, body composition, or increased muscle strength from caffeine supplementation,” they noted. “Further research is necessary to elucidate possible mechanisms, especially the hypothetical role of fiber-type predominance and its influence on the variability of the caffeine response.”
Source: Nutrients; doi: 10.3390/nu18050801;“Caffeine Supplementation Increases Muscle Strength, but Not Endurance, While Both Caffeine and Its Expectation Elevate Blood Lactate: A Balanced-Placebo Design Study.” Authors: E.M.K.V.K. et al.
