Placebo effect on sports and cognitive performance after conditioning to caffeine supplementation

Abstract

Historically, placebos are understood as inert interventions, and for this reason they would not have any effect on the body. Placebos started to be used as a comparator in clinical trials in order to identify the effectiveness of interventions. However, with the advancement of science, it became clear that the placebo effect is a measurable phenomenon, which can lead to beneficial effects on the body. There are several factors capable of enhancing the placebo effect, such as personality, context, expectation and, as recent evidence suggests, conditioning. Conditioning is when repeated doses of a certain substance are replaced by a placebo. Studies performed with injectable analgesics, such as morphine, identified similar physiological changes between placebos, after conditioning, and the real substance. Food supplements, especially caffeine, are widely used with the objective of improving sports performance. The main justification for the ergogenicity of substances is the fact that they and their metabolites are adenosine receptor antagonists, which leads to an increase in the release of catecholamines, generating an increase in psychomotor agitation and a reduction in the perception of pain, converging to improve sports performance. Although such mechanisms are well established, no study has evaluated the placebo effect after caffeine conditioning and its responses on physiological parameters and sports and cognitive performance. The hypothesis is that caffeine conditioning enhances the placebo effect, leading to improved performance and physiological changes similar to those found with caffeine supplementation, even if the substance is not administered. To test this hypothesis, the present study will recruit n = 48 male cyclists, aged 18 to 40 years, healthy and with low caffeine consumption. Participants will be randomized into four parallel groups a) no treatment; b) placebo; c) caffeine conditioning; d) conditioning control. For all groups, six visits to the laboratory will be carried out, with two familiarization sessions and four main sessions. In all of them, volunteers will complete a cognitive test and a 1-km time trial, respectively. Furthermore, blood samples will be collected for evaluation of plasma xanthines and catecholamines. Expectation, side effects and food consumption questionnaires will be applied. Data will be analyzed using a mixed model of repeated measures to detect differences on performance variables. (AU)