The Impact of Expectations on Physical Performance and Psychophysiological Potential: a Randomized, Double-blind, Placebo-controlled Crossover Study on the Placebo Effect in the Context of Caffeine Supplementation
试验速览
- 阶段
- 不适用
- 状态
- 尚未招募
- 发起方
- 入组人数
- 80
- 试验地点
- 1
- 主要终点
- Physical Work Capacity (total work in J)
研究概览
简要总结
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.
详细描述
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.
研究设计
- 研究类型
- Interventional
- 分配方式
- Randomized
- 干预模型
- Crossover
- 主要目的
- Basic Science
- 盲法
- Quadruple (Participant, Care Provider, Investigator, Outcomes Assessor)
入排标准
- 年龄范围
- 20 Years 至 35 Years（Adult）
- 性别
- All
- 接受健康志愿者
- 是
入选标准
- •Age between 20 and 35 years,
- •Healthy adults,
- •Regular physical activity, but not professional athletes,
- •Normal or corrected-to-normal vision,
- •Habitual caffeine consumption.
排除标准
- •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.
研究组 & 干预措施
Sequence ABAB
Participants follow the sequence: Caffeine, Placebo, Caffeine, Placebo, with a 7-day washout period between sessions.
干预措施: Placebo (Starch capsule) (Other)
Sequence AABB
Participants follow the sequence: Caffeine, Caffeine, Placebo, Placebo, with a 7-day washout period between sessions.
干预措施: Caffeine (6mg/kg) (Drug)
Sequence BBAA
Participants follow the sequence: Placebo, Placebo, Caffeine, Caffeine, with a 7-day washout period between sessions.
干预措施: Caffeine (6mg/kg) (Drug)
Sequence ABAB
Participants follow the sequence: Caffeine, Placebo, Caffeine, Placebo, with a 7-day washout period between sessions.
干预措施: Caffeine (6mg/kg) (Drug)
Sequence BABA
Participants follow the sequence: Placebo, Caffeine, Placebo, Caffeine, with a 7-day washout period between sessions.
干预措施: Caffeine (6mg/kg) (Drug)
Sequence BABA
Participants follow the sequence: Placebo, Caffeine, Placebo, Caffeine, with a 7-day washout period between sessions.
干预措施: Placebo (Starch capsule) (Other)
Sequence AABB
Participants follow the sequence: Caffeine, Caffeine, Placebo, Placebo, with a 7-day washout period between sessions.
干预措施: Placebo (Starch capsule) (Other)
Sequence BBAA
Participants follow the sequence: Placebo, Placebo, Caffeine, Caffeine, with a 7-day washout period between sessions.
干预措施: Placebo (Starch capsule) (Other)
结局指标
主要结局
Physical Work Capacity (total work in J)
时间窗: 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.
Psychomotor Vigilance Test Reaction Time (ms)
时间窗: 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)
时间窗: 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).
Postural Control (mm)
时间窗: 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).
Explosive power variables (mm)
时间窗: 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.
次要结局
- Exercise Heart Rate (bpm)(Measured continuously during each laboratory exercise protocol (approximately 85-120 minutes).)
- Exercise Heart Rate Variability (ms)(Measured continuously during each laboratory exercise protocol (approximately 85-120 minutes).)
- 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 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 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.)
- 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).)
- Heart Rate Recovery (bpm)(Measured continuously during the first 5 minutes immediately following exercise cessation.)
- Postural Control (mm)(Measured continuously during the exercise protocol and at T1 (minute 2), T2 (minute 55), and T3 (minute 125).)
- 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.)
- Personality Traits (NEO-FFI, points)(Measured at baseline (first study visit).)
- Mood State (POMS/BRUMS) (points)(Measured during each laboratory study visit.)
- Caffeine Expectancy (Caff-EQ-Brief) (points)(Measured 30 minutes post-ingestion.)
- Urine pH(Measured once prior to the start of each laboratory study visit.)
- White blood cells count and differential (count/L)(Measured at baseline (pre-supplementation), 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.)
- Hematological indices (red blood cells, RBC) (count/L)(Measured at baseline (pre-supplementation), 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.)
- Hematological indices (hematocrit, HCT) (L/L)(Measured at baseline (pre-supplementation), 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.)
- Hematological indices (mean corpuscular hemoglobin mass, MCH) (fmol)(Measured at baseline (pre-supplementation), 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.)
- Hematological indices (platelet count, PLT) (count/L)(Measured at baseline (pre-supplementation), 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.)
- CAF and PAX concentrations (µmol/L)(Measured at baseline (pre-supplementation), 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.)
- 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.)
- Urea Concentration (mmol/L)(Measured at baseline (pre-supplementation), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise.)
- Glucose Concentration (mg/dL)(Measured at baseline (pre-supplementation), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise.)
- Creatinine concentration (μmol/L)(Measured at baseline (pre-supplementation), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise.)
- 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.)
- Lactate concentration (mmol/L)(Measured at baseline (pre-supplementation), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise.)
- Electrolites' concentration (Ca, Na, K, Cl) (mmol/L)(Measured at baseline (pre-supplementation), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise.)
- Blood pH(Measured at baseline (pre-supplementation), 30 minutes post-ingestion, before exercise, and 3 minutes post-exercise.)
- 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.)
- Static weight distribution (mm)(Measured at the start of each study visit.)
- Analysis of body composition (fat-free mass, fat mass) (kg)(Measured at the start of each study visit.)
- Analysis of body composition (total body water) (L)(Measured at the start of each study visit.)
- Analysis of body composition (total body water) (%)(Measured 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).)
- Anthropometric Indices (kg)(Measured at the start of each study visit.)
- Anthropometric Indices (metres)(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 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 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).)
- Hydration Status (g/mL)(Once prior to the start of each laboratory study visit.)
- 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).)
- 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).)
- 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).)
- Heart Rate Variability Recovery (ms)(Measured continuously during the first 5 minutes immediately following exercise cessation.)
- Caffeine Expectancy Questionnaire Score (points)(Measured 30 minutes post-ingestion.)
- Suggestibility (SSS) (points)(Measured during the last study visit.)
- Intrinsic Motivation (IMI) (points)(Measured after each test block during every laboratory study visit.)
- Sport Motivation (SMS) (points)(Measured during the first study visit.)
- Sleep Quality (LSEQ) (points)(Measured once during each laboratory study visit.)
- Salivary Cortisol Concentration (nmol/L)(Measured at baseline (pre-supplementation), 30 minutes post-ingestion, before warm-up (60 minutes post-ingestion), 3 minutes post-exercise, and 10 minutes post-exercise.)
- Salivary Testosterone Concentration (pmol/L)(Measured at baseline (pre-supplementation), 30 minutes post-ingestion, before warm-up (60 minutes post-ingestion), 3 minutes post-exercise, and 10 minutes post-exercise.)
- Salivary Alpha-amylase Activity (U/L)(Measured at baseline (pre-supplementation), 30 minutes post-ingestion, before warm-up (60 minutes post-ingestion), 3 minutes post-exercise, and 10 minutes post-exercise.)