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Placebo effects and physical performance: central and peripheral mechanisms investigated by different experimental designs

Grant number: 20/04827-0
Support type:Scholarships in Brazil - Doctorate
Effective date (Start): May 01, 2021
Effective date (End): April 30, 2024
Field of knowledge:Health Sciences - Physical Education
Principal researcher:Flávio de Oliveira Pires
Grantee:Cayque Brietzke Barreto
Home Institution: Instituto de Saúde e Sociedade (ISS). Universidade Federal de São Paulo (UNIFESP). Campus Baixada Santista. Santos , SP, Brazil


Research method handbooks consider double-blind Randomized Controlled Trials (RCTs) gold-standard for drug investigation and interventions. However, this type of design presents a bias derived from the participant's expectation about the ingested substance, which may cause a phenomenon called placebo effect. In the physical exercise scenario, a substance commonly used to improve performance is caffeine. However, studies have suggested a possible placebo effect of its use, although there is still no solid mechanistic basis to explain this effect. The aim of this study is to compare the central (i.e., Central and Peripheral Nervous System (CNS and PNS, respectively)) and peripheral (muscle and mechanical responses) mechanisms of the placebo effect of caffeine in an RCT and in a placebo perceived-as-caffeine design. For this, 16 participants will perform 8 sessions: 1) participants will be familiarized with the study procedures; 2 - 3) measurement error estimate and control measures (session 3); 4 - 7) comparison of the placebo effect in an RCT vs a placebo perceived-as-caffeine design; 8) caffeine session as a form of positive control of the study. In sessions 4 - 8, participants will perform 5 maximum voluntary contractions before and 45 minutes after the capsules ingestion to assess SNP and torque measurements, and after that they will perform 10 series of 10 submaximal voluntary contractions to assess SNC responses. CNS (EEG) and SNP responses such as the corticospinal excitability (V-wave) will be obtained together with the muscular responses (EMG). The hypothesis is that there is a placebo effect in both experimental designs, but with greater magnitude when participants have their expectations manipulated towards the beneficial effect of caffeine. (AU)

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