Cognitive Performance, Physical Performance, Placebo Effect
Conditions
Keywords
Caffeine, Expectancy, Psychophysiology, Exercise PHysiology, Postural Control, Human Performance
Brief summary
This study aims to determine the impact of the placebo (PLA) effect on physical and cognitive performance in a controlled laboratory setting. The study investigates how expectations and beliefs about substance intake (caffeine vs. placebo) interact with actual consumption to influence performance and physiological stress markers. Healthy adults (n = 80) will participate in four testing sessions using a randomized, double-blind, placebo-controlled crossover design. Physiological stress markers (cortisol and alpha-amylase), heart rate, and performance metrics will be monitored during a standardized cycling exercise protocol. This phase provides the dense mechanistic data required to refine a mathematical model of the placebo effect, offering insights into how individual personality traits and cognitive anchoring influence psychophysiological potential.
Detailed description
This study employs a randomized, double-blind, placebo-controlled crossover design to conduct a multifactorial analysis of psychophysiological and biomechanical dynamics. Participants (n = 80, aged 20-35 years) will complete four experimental sessions separated by 7-day washout periods, involving caffeine (6 mg/kg) or placebo administration. The laboratory protocol (160 minutes) integrates multiple modalities: (1) cognitive testing (Reaction Time Test and Flanker Test), (2) postural control assessment using the BTrackS Balance Plate, and (3) a standardized cycle ergometer exercise protocol consisting of 15 minutes at the anaerobic threshold followed by a 5-minute self-paced maximal effort trial. Belief manipulation (immediate vs. retrospective reporting) and cognitive anchoring (feedback conditions) are implemented to isolate expectancy-driven effects. Continuous metabolic and cardiorespiratory data collected using the Cosmed K5 system will be synchronized with blood biomarkers (lactate, glucose, caffeine, and paraxanthine) and salivary biomarkers (cortisol, testosterone, and alpha-amylase). Advanced statistical methods, including Functional Data Analysis (FDA) and machine learning, will be used to integrate physiological trajectories with behavioral predictors.
Interventions
Anhydrous caffeine administered in an encapsulated form at a dosage of 6 mg per kilogram of body mass, 60 minutes before the exercise protocol.
Corn starch administered in an identical encapsulated form as the active caffeine, 60 minutes prior to the laboratory exercise protocol.
Sponsors
Poznan University of Physical Education
Study design
Allocation
RANDOMIZED
Intervention model
CROSSOVER
Primary purpose
BASIC_SCIENCE
Masking
QUADRUPLE (Subject, Caregiver, Investigator, Outcomes Assessor)
Intervention model description
Participants are divided into two MetaGroups (MG1 and MG2). MG1 follows a fully blinded crossover design (sequences AABB or BBAA), while MG2 follows a partially blinded mixed design (sequences ABAB or BABA), with all participants undergoing four experimental sessions separated by a 7-day washout period.
Eligibility
Sex/Gender
ALL
Age
20 Years to 30 Years
Healthy volunteers
Yes
Inclusion criteria
* Age between 20 and 30 years, * Healthy adults, * Regular physical activity, but not professional athletes, * 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.
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| Physical Work Capacity (total work in J) | Measured during each laboratory exercise protocol (approximately 85-120 minutes). | Total physical work performed, expressed in Joules (J), during the standardized laboratory exercise protocol, including both the Anaerobic Threshold phase and the Self-paced Maximal Time-trial. |
Secondary
| Measure | Time frame | Description |
|---|---|---|
| Exercise Heart Rate (bpm) | Measured continuously during each laboratory exercise protocol (approximately 85-120 minutes). | Heart rate expressed in beats per minute (bpm) recorded continuously throughout the standardized laboratory exercise protocol. |
| Exercise Heart Rate Variability (ms) | Measured continuously during each laboratory exercise protocol (approximately 85-120 minutes). | Heart rate variability expressed in milliseconds (ms) and recorded continuously throughout the standardized laboratory exercise protocol to assess autonomic regulation. |
| Salivary Cortisol Concentration (nmol/L) | Measured at baseline (pre-supplementation), 30 minutes post-ingestion, after warm-up (60 minutes post-ingestion), and 3 minutes post-exercise. | Salivary cortisol concentration expressed in nmol/L. |
| Salivary Testosterone Concentration (pmol/L) | Measured at baseline (pre-supplementation), 30 minutes post-ingestion, after warm-up (60 minutes post-ingestion), and 3 minutes post-exercise. | Salivary testosterone concentration expressed in pmol/L. |
| Salivary Alpha-amylase Activity (U/L) | Measured at baseline (pre-supplementation), 30 minutes post-ingestion, after warm-up (60 minutes post-ingestion), and 3 minutes post-exercise. | Salivary alpha-amylase activity expressed in U/L. |
| Simple Reaction Time (ms) | Measured at T1 (pre-ingestion, minute 2 of the protocol), T2 (post-ingestion/pre-exercise, minute 55 of the protocol), and T3 (post-exercise, minute 125 of the protocol). | Reaction time during the Simple Reaction Time test expressed in milliseconds (ms). |
| Heart Rate Recovery (bpm) | Measured continuously during the first 5 minutes immediately following exercise cessation. | Heart rate recorded during the post-exercise recovery period, expressed in beats per minute (bpm). |
| Postural Control (mm) | Measured continuously during the exercise protocol and at T1 (minute 2), T2 (minute 55), and T3 (minute 125). | Center of Pressure excursions measured using the BTrackS Balance Plate and expressed in millimeters (mm). |
| Rating of Perceived Exertion (Borg Scale, points) | Before and immediately after warm-up, immediately after the Anaerobic Threshold phase, immediately after the Self-paced Maximal Time-trial, and immediately after cooldown during each laboratory study visit. | Perceived exertion will be assessed using the Borg Rating of Perceived Exertion Scale and reported in points (6-20). |
| Personality Traits (NEO-FFI, points) | Measured at baseline (first study visit). | Personality traits will be assessed using the NEO Five-Factor Inventory (NEO-FFI). The questionnaire provides scores for five personality domains: Neuroticism, Extraversion, Openness to Experience, Agreeableness, and Conscientiousness. Results will be reported as domain scores in points. |
| Mood State (POMS/BRUMS) (points) | Measured during each laboratory study visit. | Mood state assessed using the Profile of Mood States (POMS/BRUMS), expressed in points. |
| Caffeine Expectancy (Caff-EQ-Brief) (points) | Measured 30 minutes post-ingestion. | Caffeine expectancy assessed using the Caffeine Expectancy Questionnaire-Brief (Caff-EQ-Brief), expressed in points. |
| Urine pH | Measured once prior to the start of each laboratory study visit. | Urine pH measured using a urine strip analyzer. |
| White blood cells count and differential (count/L) | Measured at baseline (pre-supplementation), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. | Assessment of the hematological parameter will be performed from fingertip capillary blood collected before supplementation (baseline), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. |
| White blood cells count and differential (%) | Measured at baseline (pre-supplementation), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. | Assessment of the hematological parameter will be performed from fingertip capillary blood collected before supplementation (baseline), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. |
| Hematological indices (red blood cells, RBC) (count/L) | Measured at baseline (pre-supplementation), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. | Assessment of the hematological parameter will be performed from fingertip capillary blood collected before supplementation (baseline), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. |
| Hematological indices (hemoglobin concentration, HGB) (mmol/L) | Measured at baseline (pre-supplementation), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. | Assessment of the hematological parameter will be performed from fingertip capillary blood collected before supplementation (baseline), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. |
| Hematological indices (hematocrit, HCT) (L/L) | Measured at baseline (pre-supplementation), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. | Assessment of the hematological parameter will be performed from fingertip capillary blood collected before supplementation (baseline), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. |
| Hematological indices (mean corpuscular volume, MCV; mean platelet volume, MPV) (fL) | Measured at baseline (pre-supplementation), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. | Assessment of the hematological parameter will be performed from fingertip capillary blood collected before supplementation (baseline), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. |
| Hematological indices (mean corpuscular hemoglobin mass, MCH) (fmol) | Measured at baseline (pre-supplementation), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. | Assessment of the hematological parameter will be performed from fingertip capillary blood collected before supplementation (baseline), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. |
| Hematological indices (mean corpuscular hemoglobin concentration, MCHC) (mmol/L) | Measured at baseline (pre-supplementation), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. | Assessment of the hematological parameter will be performed from fingertip capillary blood collected before supplementation (baseline), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. |
| Hematological indices (platelet count, PLT) (count/L) | Measured at baseline (pre-supplementation), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. | Assessment of the hematological parameter will be performed from fingertip capillary blood collected before supplementation (baseline), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. |
| Hematological indices (platelet hematocrit, PCT) (cL/L) | Measured at baseline (pre-supplementation), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. | Assessment of the hematological parameter will be performed from fingertip capillary blood collected before supplementation (baseline), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. |
| Hematological indices (platelet distribution width, PDW; platelet large cell ratio, PLCR; red blood cells distribution width - coefficient of variation, RDW-C) (%) | Measured at baseline (pre-supplementation), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. | Assessment of the hematological parameter will be performed from fingertip capillary blood collected before supplementation (baseline), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. |
| Hematological indices (red blood cells distribution width - standard deviation, RDW-S) (fL) | Measured at baseline (pre-supplementation), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. | Assessment of the hematological parameter will be performed from fingertip capillary blood collected before supplementation (baseline), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. |
| Urea Concentration (mmol/L) | Measured at baseline (pre-supplementation), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. | Urea concentration measured from fingertip capillary blood and expressed in mmol/L. |
| Glucose Concentration (mg/dL) | Measured at baseline (pre-supplementation), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. | Glucose concentration measured from fingertip capillary blood and expressed in mg/dL. |
| Creatinine concentration (μmol/L) | Measured at baseline (pre-supplementation), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. | Creatinine concentration measured from fingertip capillary blood and expressed in µmol/L. |
| Muscle damage markers (activity of alanine aminotransferase, aspartate aminotransferase, creatine kinase, lactate dehydrogenase) (U/L) | Measured at baseline (pre-supplementation), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. | Assessment of the muscle damage markers (activity of alanine aminotransferase, aspartate aminotransferase, creatine kinase, lactate dehydrogenase) (U/L) will be performed from fingertip capillary blood. |
| Lactate concentration (mmol/L) | Measured at baseline (pre-supplementation), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. | Blood lactate concentration measured from fingertip capillary blood and expressed in mmol/L. |
| Electrolites' concentration (Ca, Na, K, Cl) (mmol/L) | Measured at baseline (pre-supplementation), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. | Assessment of electrolites' concentration (Ca, Na, K, Cl) (mmol/L) will be performed from fingertip capillary blood. |
| Blood pH | Measured at baseline (pre-supplementation), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. | Assessment of gasometry markers (blood pH) will be performed from fingertip capillary blood. |
| Partial Pressure of Carbon Dioxide and Oxygen (pCO2, pO2) (mmHg) | Measured at baseline (pre-supplementation), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. | Assessment of gasometry markers (pCO2, pO2) (mmHg) will be performed from fingertip capillary blood. |
| CAF and PAX concentrations (µmol/L) | Measured at baseline (pre-supplementation), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise. | Assessment of caffeine and paraxanthine concentrations (µmol/L) will be performed from fingertip capillary blood. |
| Static weight distribution (mm) | Measured at the start of each study visit. | Static weight distribution expressed in millimeters of Center of Pressure symmetry. |
| Analysis of body composition (fat-free mass, fat mass) (kg) | Measured at the start of each study visit. | Assessment of body composition (fat-free mass, fat mass) (kg) will be carried out at the start of each study visit. |
| Analysis of body composition (total body water) (L) | Measured at the start of each study visit. | Assessment of body composition (total body water) (L) will be carried out at the start of each study visit. |
| Analysis of body composition (total body water) (%) | Measured at the start of each study visit. | Assessment of body composition (total body water) (%) will be carried out at the start of each study visit. |
| Autonomic Response during Cognitive Performance (bpm) | Measured at three time points: T1 (pre-ingestion; 2 minute of protocol), T2 (post-ingestion/pre-exercise; 55 minute of protocol), and T3 (post-exercise; 125 minute of protocol). | Heart rate and heart rate variability recording during cognitive testing blocks, expressed in beats per minute (bpm). |
| Anthropometric Indices (kg) | Measured at the start of each study visit. | Body mass in kilograms will be measured at the start of each study visit. |
| Anthropometric Indices (metres) | Measured at the start of each study visit. | Height in metres will be measured at the start of each study visit. |
| Explosive power variables (ms) | Continuous recording throughout the exercise protocol and discrete assessments at T1 (2 minute of protocol), T2 (55 minute of protocol), and T3 (125 minute of protocol). | Explosive lower-limb power variables expressed in milliseconds (ms) - Countermovement Jump - contact time and flight time. |
| Explosive power variables (W) | Continuous recording throughout the exercise protocol and discrete assessments at T1 (2 minute of protocol), T2 (55 minute of protocol), and T3 (125 minute of protocol). | Explosive lower-limb power expressed in Watts (W) - Countermovement Jump - power. |
| Explosive power variables (mm) | Continuous recording throughout the exercise protocol and discrete assessments at T1 (2 minute of protocol), T2 (55 minute of protocol), and T3 (125 minute of protocol). | Explosive lower-limb power expressed in millimeters (mm) - Countermovement Jump - height. |
| Hydration Status (g/mL) | Once prior to the start of each laboratory study visit. | Assessment of urine specific gravity (g/mL) using a urine strip analyzer. |
| Psychomotor Vigilance Test Reaction Time (ms) | Measured at T1 (pre-ingestion, minute 2 of the protocol), T2 (post-ingestion/pre-exercise, minute 55 of the protocol), and T3 (post-exercise, minute 125 of the protocol). | Reaction time during the Psychomotor Vigilance Test expressed in milliseconds (ms). |
| Flanker Test Reaction Time (ms) | Measured at T1 (pre-ingestion, minute 2 of the protocol), T2 (post-ingestion/pre-exercise, minute 55 of the protocol), and T3 (post-exercise, minute 125 of the protocol). | Reaction time during the Flanker Test expressed in milliseconds (ms). |
| Flanker Test Accuracy (%) | Measured at T1 (pre-ingestion, minute 2 of the protocol), T2 (post-ingestion/pre-exercise, minute 55 of the protocol), and T3 (post-exercise, minute 125 of the protocol). | Accuracy during the Flanker Test expressed as the percentage of correct responses. |
| Heart Rate Variability Recovery (ms) | Measured continuously during the first 5 minutes immediately following exercise cessation. | Heart rate variability expressed in milliseconds (ms) during the post-exercise recovery period. |
| Caffeine Expectancy Questionnaire Score (points) | Measured 30 minutes post-ingestion. | Caffeine expectancy assessed using the Caffeine Expectancy Questionnaire and expressed in points. |
| Suggestibility (SSS) (points) | Measured during the last study visit. | General suggestibility assessed using the Short Suggestibility Scale (SSS), expressed in points. |
| Intrinsic Motivation (IMI) (points) | Measured after each test block during every laboratory study visit. | Task-specific intrinsic motivation assessed using the Intrinsic Motivation Inventory (IMI), expressed in points. |
| Sport Motivation (SMS) (points) | Measured during the first study visit. | Sport motivation assessed using the Sport Motivation Scale (SMS), expressed in points. |
| Sleep Quality (LSEQ) (points) | Measured once during each laboratory study visit. | Subjective sleep quality assessed using the Leeds Sleep Evaluation Questionnaire (LSEQ), expressed in points. |
Countries
Poland
Contacts
CONTACTJakub Malik, PhD
PRINCIPAL_INVESTIGATORJakub Malik, PhD
Poznan University of Physical Education, Department of Sports Psychology
Outcome results
None listed