The Acute Effects of Dietary Nitrate (Beetroot Juice), Caffeine, and Their Combination on Discipline-Specific Exercise Performance, Lactate Kinetics, and Physiological Responses in Trained Functional Fitness Athletes and Elite Junior Swimmers.
Trial Snapshot
- Phase
- Not Applicable
- Status
- Not yet recruiting
- Sponsor
- Enrollment
- 112
- Locations
- 1
- Primary Endpoint
- Exercise Performance Time (minutes and seconds, Cohort A - Hyrox P'F'T)
Study Overview
Brief Summary
The purpose of this study is to investigate the acute, separate, and combined ergogenic effects of dietary nitrate (beetroot juice, BJ) and caffeine (CAF) supplementation on discipline-specific athletic performance. The project employs a double-blind, randomized, placebo-controlled, four-arm crossover design. It evaluates two highly distinct, heterogeneous populations of athletes: (A) adult high-intensity functional training (HIFT/CrossFit/Hyrox) competitors performing the standardized Hyrox Physical Fitness Test (P'F'T), and (B) elite junior competitive swimmers (National Team members) performing a progressive 8 × 100 m swimming test. The study will assess physical performance, lactate kinetics, subjective exertion, biochemical indices, psychological metrics, and gastrointestinal tolerance.
Detailed Description
This project addresses a critical gap in sports nutrition literature regarding the potential synergistic, additive, or antagonistic interactions of caffeine (CAF) and dietary nitrate (beetroot juice, BJ) when co-administered. While CAF acts primarily as an adenosine receptor antagonist in the central nervous system to enhance motor unit recruitment and decrease perceived exertion, BJ acts as a physiological precursor to nitric oxide, improving peripheral muscle contractility, mitochondrial efficiency, and muscle perfusion.
To evaluate whether these effects are universal or discipline-specific, the trial employs a two-population cohort design:
- Cohort A (HIFT/Hyrox): Investigates adult functional fitness athletes (aged 18-45) characterized by concurrent strength and endurance adaptations. They will perform the ecological Hyrox P'F'T.
- Cohort B (Elite Junior Swimmers): Investigates elite junior national team swimmers (aged 16-19) during their centralized training camp. They will undergo the standardized progressive 8 × 100 m step-test.
Furthermore, this study will analyze whether individual hematological markers (iron status) and biochemical profiles correlate with the magnitude of the ergogenic response to establish prospective predictive biomarkers for customized sports nutrition.
Study Design
- Study Type
- Interventional
- Allocation
- Randomized
- Intervention Model
- Crossover
- Primary Purpose
- Basic Science
- Masking
- Quadruple (Participant, Care Provider, Investigator, Outcomes Assessor)
Eligibility Criteria
- Ages
- 16 Years to 45 Years (Child, Adult)
- Sex
- All
- Accepts Healthy Volunteers
- Yes
Inclusion Criteria
- •A) Cohort A (HIFT / CrossFit / Hyrox):
- •Aged 18-45 years.
- •Minimum of 2 years of systematic HIFT/CrossFit/Hyrox training experience.
- •Performing >4 training sessions per week.
- •Ability to perform the HYROX Physical Fitness Test (P'F'T) and has participated in at least one official HYROX event.
- •Possession of a valid medical certificate proving eligibility for competitive sports.
- •B) Cohort B (Competitive Junior Swimmers):
- •Aged 16-19 years.
- •Active member of the Polish Junior National Swimming Team.
- •Minimum of 5 years of competitive swimming experience.
- •Current training volume of at least 8-10 pool training sessions per week.
- •Written informed consent obtained from both the participant and their legal guardian (for minors under 18).
- •C)Common Criteria for Both Cohorts:
- •No history of cardiovascular, respiratory, metabolic, or musculoskeletal disease contradicting high-intensity exercise or stimulant intake.
- •No known food allergies or adverse reactions to beetroot products or caffeine.
- •No current use of medications that alter nitrate/caffeine metabolism (e.g., proton pump inhibitors, antibiotics, phosphodiesterase inhibitors).
- •History of uneventful habituation to caffeine use during training/competition.
- •Willingness to abstain from dietary supplements, antibacterial mouthwashes, alcohol, and high-nitrate foods for 48 hours prior to each testing session.
- •Good general health and physical well-being.
Exclusion Criteria
- •(Applicable to both cohorts):
- •Occurrence of acute musculoskeletal injury or trauma during the study period.
- •Any medical or health contraindications (including severe menstrual disorders, planned pregnancy, or breastfeeding).
- •Failure or refusal to strictly adhere to the dietary, supplementation, and exercise testing protocols.
Arms & Interventions
PLCAF + BJ (Placebo CAF + Beetroot Juice)
Participants ingest a concentrated beetroot juice shot (~6.4 mmol / 400 mg nitrates) 3 hours before exercise, and a placebo capsule (maltodextrin) 60 minutes before exercise.
Intervention: Dietary Nitrate (Beetroot Juice) (Dietary Supplement)
PLCAF + PLBJ (Double Placebo Control)
Participants ingest a nitrate-depleted beetroot juice shot (~0.04 mmol nitrates) 3 hours before exercise, and a placebo capsule (maltodextrin) 60 minutes before exercise.
Intervention: Placebo (Nitrate-Depleted Beetroot Juice) (Dietary Supplement)
CAF + BJ (Active Co-ingestion)
Participants ingest a concentrated beetroot juice shot (~6.4 mmol / 400 mg nitrates) 3 hours before exercise, and a capsule of caffeine (Cohort A: 6 mg/kg body mass; Cohort B: 3 mg/kg body mass) 60 minutes before exercise.
Intervention: Dietary Nitrate (Beetroot Juice) (Dietary Supplement)
CAF + PLBJ (Caffeine + Placebo BJ)
Participants ingest a nitrate-depleted beetroot juice shot (~0.04 mmol nitrates) 3 hours before exercise, and a capsule of caffeine (Cohort A: 6 mg/kg body mass; Cohort B: 3 mg/kg body mass) 60 minutes before exercise.
Intervention: Placebo (Nitrate-Depleted Beetroot Juice) (Dietary Supplement)
PLCAF + BJ (Placebo CAF + Beetroot Juice)
Participants ingest a concentrated beetroot juice shot (~6.4 mmol / 400 mg nitrates) 3 hours before exercise, and a placebo capsule (maltodextrin) 60 minutes before exercise.
Intervention: Placebo (Maltodextrin Capsule) (Dietary Supplement)
PLCAF + PLBJ (Double Placebo Control)
Participants ingest a nitrate-depleted beetroot juice shot (~0.04 mmol nitrates) 3 hours before exercise, and a placebo capsule (maltodextrin) 60 minutes before exercise.
Intervention: Placebo (Maltodextrin Capsule) (Dietary Supplement)
CAF + BJ (Active Co-ingestion)
Participants ingest a concentrated beetroot juice shot (~6.4 mmol / 400 mg nitrates) 3 hours before exercise, and a capsule of caffeine (Cohort A: 6 mg/kg body mass; Cohort B: 3 mg/kg body mass) 60 minutes before exercise.
Intervention: Caffeine (Dietary Supplement)
CAF + PLBJ (Caffeine + Placebo BJ)
Participants ingest a nitrate-depleted beetroot juice shot (~0.04 mmol nitrates) 3 hours before exercise, and a capsule of caffeine (Cohort A: 6 mg/kg body mass; Cohort B: 3 mg/kg body mass) 60 minutes before exercise.
Intervention: Caffeine (Dietary Supplement)
Outcomes
Primary Outcomes
Exercise Performance Time (minutes and seconds, Cohort A - Hyrox P'F'T)
Time Frame: At each experimental visit (Visits T1-T4), with visits conducted at 7-day intervals following the baseline/familiarization visit (T0).
Total time (in minutes and seconds) required to complete the standardized HYROX Physical Fitness Test (P'F'T) consisting of 6 specific functional exercises.
Swimming Performance (minutes and seconds, Cohort B - 8x100m Step-Test)
Time Frame: At each experimental visit (Visits T1-T4), with visits conducted at 7-day intervals following the baseline/familiarization visit (T0).
Swimming performance will be assessed using the completion time (seconds and milliseconds) for each 100-m repetition of the standardized 8 × 100-m step test, including the maximal-effort repetition performed during the fifth stage.
Secondary Outcomes
- Blood Lactate Kinetics (mmol/L)(Before supplementation (baseline), pre-exercise (3 hours after beetroot juice supplementation and 30 minutes after caffeine supplementation), and 3 and 7 minutes after exercise at each experimental visit (Visits T1-T4; 7-day intervals).)
- Heart Rate (HR, bpm)(Continuously monitored during exercise at each experimental visit (Visits T1-T4; 7-day intervals).)
- Rating of Perceived Exertion (RPE, points)(Immediately after exercise at each experimental visit (Visits T1-T4; 7-day intervals).)
- Blood Pressure (mmHg)(Measured 2.5 hours after beetroot juice supplementation and 30 minutes after caffeine supplementation (pre-exercise) at each experimental visit (Visits T1-T4; 7-day intervals).)
- Gastrointestinal Tolerance Profile (mVAS, points)(Measured 30 minutes after supplementation and immediately after exercise at each experimental visit (Visits T1-T4; 7-day intervals).)
- White blood cells count and differential (count/L)(Before supplementation (baseline) and 3 minutes after exercise at each experimental visit (Visits T1-T4; 7-day intervals).)
- White blood cells count and differential (%)(Before supplementation (baseline) and 3 minutes after exercise at each experimental visit (Visits T1-T4; 7-day intervals).)
- Hematological indices (red blood cells, RBC) (count/L)(Before supplementation (baseline) and 3 minutes after exercise at each experimental visit (Visits T1-T4; 7-day intervals).)
- Hematological indices (hemoglobin concentration, HGB) (mmol/L)(Before supplementation (baseline) and 3 minutes after exercise at each experimental visit (Visits T1-T4; 7-day intervals).)
- Hematological indices (hematocrit, HCT) (L/L)(Before supplementation (baseline) and 3 minutes after exercise at each experimental visit (Visits T1-T4; 7-day intervals).)
- Hematological indices (mean corpuscular volume, MCV; mean platelet volume, MPV) (fL)(Before supplementation (baseline) and 3 minutes after exercise at each experimental visit (Visits T1-T4; 7-day intervals).)
- Hematological indices (mean corpuscular hemoglobin mass, MCH) (fmol)(Before supplementation (baseline) and 3 minutes after exercise at each experimental visit (Visits T1-T4; 7-day intervals).)
- Hematological indices (mean corpuscular hemoglobin concentration, MCHC) (mmol/L)(Before supplementation (baseline) and 3 minutes after exercise at each experimental visit (Visits T1-T4; 7-day intervals).)
- Hematological indices (platelet count, PLT) (count/L)(Before supplementation (baseline) and 3 minutes after exercise at each experimental visit (Visits T1-T4; 7-day intervals).)
- Hematological indices (platelet hematocrit, PCT) (cL/L)(Before supplementation (baseline) and 3 minutes after exercise at each experimental visit (Visits T1-T4; 7-day intervals).)
- Hematological indices (platelet distribution width, PDW; platelet large cell ratio, PLCR; red blood cells distribution width - coefficient of variation, RDW-C) (%)(Before supplementation (baseline) and 3 minutes after exercise at each experimental visit (Visits T1-T4; 7-day intervals).)
- Hematological indices (red blood cells distribution width - standard deviation, RDW-S) (fL)(Before supplementation (baseline) and 3 minutes after exercise at each experimental visit (Visits T1-T4; 7-day intervals).)
- Nutritional status indices (concentration of urea) (mmol/L)(Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals).)
- Creatinine Concentration (μmol/L)(Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals).)
- Muscle Damage Markers (ALT, AST, CK, LDH) (U/L)(Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals).)
- Body composition (fat-free mass, fat mass) (kg)(Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals).)
- Body composition (fat-free mass, fat mass) (%)(Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals).)
- Body composition (total body water) (L)(Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals).)
- Body composition (total body water) (%)(Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals).)
- Iron Status (Iron, Ferritin, UIBC, TIBC) (μg/dL)(Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals).)
- Iron Status (Transferrin Concentration) (g/L)(Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals).)
- Sleep Quality (Visual Analog Scale, VAS; points)(Before supplementation (baseline), pre-exercise, and immediately after exercise at each experimental visit (Visits T1-T4; 7-day intervals).)
- Mood (Brunel Mood Scale, BRUMS; points)(Before supplementation (baseline), pre-exercise, and immediately after exercise at each experimental visit (Visits T1-T4; 7-day intervals).)
- Competitive State Anxiety (Revised Competitive State Anxiety Inventory-2, CSAI-2R; points)(Before supplementation (baseline), pre-exercise, and immediately after exercise at each experimental visit (Visits T1-T4; 7-day intervals).)
- Felt Arousal (Felt Arousal Scale, FAS; points)(Before supplementation (baseline), pre-exercise, and immediately after exercise at each experimental visit (Visits T1-T4; 7-day intervals).)
- Feeling Scale (FS; points)(Before supplementation (baseline), pre-exercise, and immediately after exercise at each experimental visit (Visits T1-T4; 7-day intervals).)