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Caffeine Expectancy Does Not Affect Interval Running Performance, Physiological Responses, or Running Kinematics in
Fernando Valero1, Fernando González-Mohíno1, Alejandro Alda-Blanco1
1Sport Training Lab, Faculty of Sport Sciences, University of Castilla-La Mancha, 45071 Toledo, Spain.
Nutrients
|August 13, 2026
Summary
Believing they consumed caffeine did not enhance running performance or physiological responses in trained athletes. However, caffeine expectancy did alter the perception of expected side effects, suggesting limited ergogenic placebo effects.
Area of Science:
- Exercise Physiology
- Sports Science
- Psychology of Sport
Background:
- The placebo effect, particularly caffeine expectancy, may influence athletic performance.
- Understanding expectancy effects is crucial for interpreting ergogenic aid studies.
Purpose of the Study:
- To investigate the placebo effect of caffeine expectancy on interval running performance in moderately trained athletes.
- To analyze the impact of caffeine expectancy on pacing, physiological responses, and perceived exertion.
Main Methods:
- Randomized crossover trial with 14 moderately trained athletes.
- Participants completed interval running sessions under placebo (described as caffeine) and control conditions.
- Evaluated running performance, pacing, heart rate, kinematics, RPE, and side effects.
Main Results:
- No significant differences in total running time, pacing, heart rate, or kinematics between placebo and control conditions.
- Athletes reported increased feelings of activeness and expected caffeine side effects (e.g., increased urination, sleep disturbance) with placebo ingestion.
- Perceived exertion (RPE) did not differ between conditions.
Conclusions:
- Caffeine expectancy alone did not improve interval running performance or physiological markers in trained runners.
- Expectancy influenced the perception of caffeine-related side effects, but not performance.
- Further research is needed to understand conditions influencing placebo effects in exercise.
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