Caffeine supplementation does not enhance jump performance: a placebo and nocebo study

Purpose : There is evidence that caffeine supplementation improves jump performance in studies where the design is randomized, counterbalanced and placebo-controlled. However, there is recent evidence that this outcome is expectation-dependent. Here, we applied a method to nullify the expectancy. Therefore, we aimed to check whether caffeine supplementation improves jump performance when nullifying the positive expectation for performance improvement. Methods : Thirty-four women participated. Participants performed squat jump and countermovement jump in four days. The first day was a control day. In the last three days, we gave the participants caffeine (6 mg. kg ^-1 ). However, we informed them that randomly and blindly, participants would receive caffeine (ergogenic), placebo (ineffective) or lactic acid (ergolytic). Results : Jump performance neither improves along the days (P>0.05) nor through different expectations (P>0.05). Still, there is a moderate chance (>75%) to observe similar performance between control and supplementation days or different expectancies. Conclusion : We conclude that caffeine supplementation does not improve jump performance in women when positive expectation is nullified.