Placebo Effect in Field-Based Physical Performance

Official title

Psychophysiological Mechanisms of the Placebo Effect on Physical Performance in Field Settings

Overview

This study aims to investigate the placebo (PLA) effect on physical performance across different sports disciplines in real-world, field-based settings. The study investigates how participant expectations and beliefs regarding caffeine (CAF) intake influence physical performance and psychomotor function outside the controlled laboratory environment. Healthy, physically active adults (n = 120) from diverse sports backgrounds will be randomly assigned to receive caffeine, placebo, or no intervention. Participants will perform discipline-specific field exercise tests (e.g., running-based protocols or repeated sprint protocols) while physiological responses are monitored using wearable technology. Physical performance outcomes and psychomotor responses will be analyzed to evaluate the real-world impact of the placebo effect and to distinguish the pharmacological effects of caffeine from those driven by psychological expectations across different athletic settings.

Detailed description

This study employs a cross-sectional design conducted in diverse field settings to investigate the placebo (PLA) effect across different sports disciplines. Participants (n = 120, aged 20-35 years) representing different training profiles (endurance and mixed) will be randomly assigned to one of three parallel groups: Caffeine, Placebo, or Control. Each participant will complete a single experimental session lasting approximately 35 minutes, consisting of: (1) baseline psychomotor assessment using the Simple Reaction Time test, (2) a discipline-specific exercise protocol (e.g., the Cooper test performed on an athletics track or a Repeated Sprint Ability protocol), and (3) post-exercise recovery monitoring. Physiological parameters, including heart rate (HR), heart rate variability (HRV), and respiratory rate (RR), together with postural stability, will be continuously monitored using wearable technology. The study will evaluate how psychological expectations influence physical performance, psychomotor function, and physiological responses during sport-specific exercise, providing evidence for the role of the placebo effect under real-world athletic conditions.

Interventions

• Drug Caffeine (6mg/kg)
  Anhydrous caffeine administered in an encapsulated form at a dosage of 6mg per kilogram of body mass, 30-60 minutes before the exercise protocol.
• Other Placebo (Starch capsule)
  Corn starch administered in an identical encapsulated form as the active caffeine, 30-60 minutes before the exercise protocol.
• Other Sham (No Treatment)
  Participants perform the same exercise protocols without any capsule or substance administration.

Primary outcome measures

• Physical Performance Capacity (total distance in running, metres) [Time frame: Measured during the exercise protocol immediately following administration of the study intervention.]
• Physical Performance Capacity (total work in Joules for cycling) [Time frame: Measured during the exercise protocol immediately following administration of the study intervention.]
• Physical Performance Capacity (exercise duration until exhaustion, minutes) [Time frame: Measured during the exercise protocol immediately following administration of the study intervention.]

Secondary outcome measures (12)

• Exercise Heart Rate (bpm) [Time frame: Continuously monitored during the exercise protocol immediately following administration of the study intervention.]
• Cognitive Heart Rate (bpm) [Time frame: Measured during cognitive testing immediately before and immediately after the exercise protocol.]
• Post-Exercise Heart Rate Recovery (bpm) [Time frame: Continuously monitored during the first 5 minutes immediately following completion of the exercise protocol.]
• Cognitive Reaction Time (ms) [Time frame: Measured immediately before and immediately after the exercise protocol.]
• Rating of Perceived Exertion (Borg Scale, points) [Time frame: Measured immediately after completion of the exercise protocol.]
• Biomechanical Kinematic Profile (cm) [Time frame: Continuously monitored during the exercise protocol immediately following administration of the study intervention.]
• Biomechanical Kinematic Profile (ms) [Time frame: Continuously monitored during the exercise protocol immediately following administration of the study intervention.]
• Biomechanical Kinematic Profile (steps/min) [Time frame: Continuously monitored during the exercise protocol immediately following administration of the study intervention.]
• Anthropometric Indices (kg) [Time frame: Measured at the start of the protocol.]
• Anthropometric Indices (m) [Time frame: Measured at the start of the protocol.]
• Body composition (fat-free mass, fat mass) (kg) [Time frame: Measured at the start of the protocol.]
• Body composition (fat-free mass, fat mass) (%) [Time frame: Measured at the start of the protocol.]

Eligibility criteria

Inclusion criteria

• Age between 20 and 35 years,
• Healthy adults,
• Regular physical activity,
• Normal or corrected-to-normal vision,
• Habitual caffeine consumption.

Exclusion criteria

• History of neurological, psychiatric, cardiovascular, or metabolic disorders,
• Current use of medication or supplements affecting the central nervous system,
• Musculoskeletal injuries that would impair physical performance,
• No habitual caffeine consumption or severe negative side effects of caffeine,
• Diagnosed sleep disorders or chronic fatigue,
• Diagnosed major depressive disorder or other severe psychiatric conditions,
• Presence of any menstrual disorders,
• Inability to attend all experimental study visits.

Criteria are shown verbatim from the registry (in English). Final eligibility is always assessed by the study center.

Healthy volunteers: Yes

Study design

Allocation

Randomized

Model

Parallel assignment

Masking

Quadruple blind

Primary purpose

Basic science

Study locations

Poland · 1 center

• Poznan University of Physical Education — Poznan

Identifiers

NCT: NCT07742150 · 152-1-26 · 2025/57/N/NZ4/04470

Primary sources (government registries)

• ClinicalTrials.gov (US NIH)

View this study on ClinicalTrials.gov ↗