Athletic Performance, Dietary Supplement, Iron Status
Conditions
Keywords
Caffeine, Sports nutrition, Swimming, High-Intensity Functional Training, Nitric oxide
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.
Interventions
DIETARY_SUPPLEMENTCaffeine
Anhydrous caffeine administered orally in a hard gelatine capsule. To address the unique physiological profiles of the two cohorts, a highly specific, differentiated dosing protocol is implemented: Cohort A (adult functional fitness athletes) will receive a high-performance dose of 6 mg/kg body mass, while Cohort B (elite junior swimmers) will receive a safe, youth-adapted dose of 3 mg/kg body mass. In all experimental trials, the capsule is ingested exactly 60 minutes prior to the onset of the discipline-specific exercise test to match peak plasma caffeine concentration.
DIETARY_SUPPLEMENTDietary Nitrate (Beetroot Juice)
Concentrated beetroot juice (BJ) administered as a single, acute organic shot of 70 mL (Beet It Sport, James White Drinks Ltd., Ipswich, UK). Each active shot contains approximately 400 mg (equivalent to \~6.4 mmol) of inorganic nitrate. In contrast to chronic loading designs, this study evaluates purely acute effects; the shot is ingested exactly 3 hours (180 minutes) prior to the physical performance test to align with peak systemic concentration of plasma nitrite.
DIETARY_SUPPLEMENTPlacebo (Maltodextrin Capsule)
Placebo capsule containing inert maltodextrin powder. The capsule is identical in size, shape, weight, color (opaque), and texture to the active caffeine capsule to ensure robust blinding. It is administered at the exact same time point (60 minutes pre-exercise) according to the identical body-mass-adjusted dosing scheme (simulating either 3 mg/kg or 6 mg/kg).
DIETARY_SUPPLEMENTPlacebo (Nitrate-Depleted Beetroot Juice)
Nitrate-depleted beetroot juice (Beet It, James White Drinks Ltd., Ipswich, UK) administered as a 70 mL shot. This placebo is identical in taste, smell, appearance, packaging, and viscosity to the active concentrated shot, but has been selectively filtered to contain negligible nitrate levels (\<0.4 mmol / \~25 mg of nitrates). It is ingested exactly 3 hours prior to the exercise test.
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
This study employs a double-blind, randomized, placebo-controlled, four-arm, crossover design to evaluate the acute, separate, and combined effects of caffeine (CAF) and dietary nitrate (beetroot juice, BJ) on athletic performance. Following a baseline familiarization session (T0), participants will complete four main experimental testing visits (T1-T4). Every participant will undergo all four interventional conditions in a randomized, counterbalanced sequence. A minimum 7-day (168-hour) washout period will separate each testing session to ensure complete physical recovery, muscle regeneration, and complete elimination of the active substances from the systemic circulation. The four interventional combinations administered across the testing visits are: Active BJ + Active CAF (CAF+BJ); Active CAF + BJ (CAF+PLBJ); Active BJ + Placebo CAF (PLCAF+BJ); Placebo BJ + Placebo CAF (PLCAF+PLBJ).
Eligibility
Sex/Gender
ALL
Age
16 Years to 45 Years
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.
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| Exercise Performance Time (minutes and seconds, Cohort A - Hyrox P'F'T) | 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) | 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
| Measure | Time frame | Description |
|---|---|---|
| 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). | Blood lactate concentration, including peak concentration, accumulation kinetics, and clearance rate, will be assessed from fingertip capillary blood collected before supplementation (baseline), pre-exercise (3 hours after beetroot juice supplementation and 30 minutes after caffeine supplementation), and post-exercise (3 and 7 minutes after exercise) at each experimental visit. |
| Heart Rate (HR, bpm) | Continuously monitored during exercise at each experimental visit (Visits T1-T4; 7-day intervals). | Real-time heart rate (beats per minute) will be continuously monitored throughout each exercise test using a telemetry-based heart rate monitoring system. |
| Rating of Perceived Exertion (RPE, points) | Immediately after exercise at each experimental visit (Visits T1-T4; 7-day intervals). | Subjective rating of perceived exertion will be assessed using the validated Borg Scale (6-20). |
| 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). | Systolic and diastolic blood pressure will be measured using an automated oscillometric blood pressure monitor. |
| Gastrointestinal Tolerance Profile (mVAS, points) | Measured 30 minutes after supplementation and immediately after exercise at each experimental visit (Visits T1-T4; 7-day intervals). | Gastrointestinal symptoms will be assessed using the modified Visual Analog Scale (mVAS; 0-10, where 0 = no symptoms and 10 = extremely severe symptoms). |
| 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). | Assessment of the hematological parameter will be performed from fingertip capillary blood collected before supplementation (baseline) and 3 minutes after exercise at each experimental visit. |
| White blood cells count and differential (%) | Before supplementation (baseline) and 3 minutes after exercise at each experimental visit (Visits T1-T4; 7-day intervals). | Assessment of the hematological parameter will be performed from fingertip capillary blood collected before supplementation (baseline) and 3 minutes after exercise at each experimental visit. |
| 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). | Assessment of the hematological parameter will be performed from fingertip capillary blood collected before supplementation (baseline) and 3 minutes after exercise at each experimental visit. |
| 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). | Assessment of the hematological parameter will be performed from fingertip capillary blood collected before supplementation (baseline) and 3 minutes after exercise at each experimental visit. |
| Hematological indices (hematocrit, HCT) (L/L) | Before supplementation (baseline) and 3 minutes after exercise at each experimental visit (Visits T1-T4; 7-day intervals). | Assessment of the hematological parameter will be performed from fingertip capillary blood collected before supplementation (baseline) and 3 minutes after exercise at each experimental visit. |
| 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). | Assessment of the hematological parameter will be performed from fingertip capillary blood collected before supplementation (baseline) and 3 minutes after exercise at each experimental visit. |
| 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). | Assessment of the hematological parameter will be performed from fingertip capillary blood collected before supplementation (baseline) and 3 minutes after exercise at each experimental visit. |
| 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). | Assessment of the hematological parameter will be performed from fingertip capillary blood collected before supplementation (baseline) and 3 minutes after exercise at each experimental visit. |
| 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). | Assessment of the hematological parameter will be performed from fingertip capillary blood collected before supplementation (baseline) and 3 minutes after exercise at each experimental visit. |
| 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). | Assessment of the hematological parameter will be performed from fingertip capillary blood collected before supplementation (baseline) and 3 minutes after exercise at each experimental visit. |
| 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). | Assessment of the hematological parameter will be performed from fingertip capillary blood collected before supplementation (baseline) and 3 minutes after exercise at each experimental visit. |
| 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). | Assessment of the hematological parameter will be performed from fingertip capillary blood collected before supplementation (baseline) and 3 minutes after exercise at each experimental visit. |
| Nutritional status indices (concentration of urea) (mmol/L) | Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals). | Urea concentration will be assessed from fingertip capillary blood collected before supplementation (baseline). |
| Creatinine Concentration (μmol/L) | Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals). | Creatinine concentration will be assessed from fingertip capillary blood collected before supplementation (baseline). |
| Muscle Damage Markers (ALT, AST, CK, LDH) (U/L) | Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals). | Activities of alanine aminotransferase (ALT), aspartate aminotransferase (AST), creatine kinase (CK), and lactate dehydrogenase (LDH) will be assessed from fingertip capillary blood collected before supplementation (baseline). |
| Body composition (fat-free mass, fat mass) (kg) | Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals). | Body composition will be assessed before supplementation (baseline) using bioelectrical impedance analysis. |
| Body composition (fat-free mass, fat mass) (%) | Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals). | Body composition will be assessed before supplementation (baseline) using bioelectrical impedance analysis. |
| Body composition (total body water) (L) | Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals). | Body composition will be assessed before supplementation (baseline) using bioelectrical impedance analysis. |
| Body composition (total body water) (%) | Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals). | Body composition will be assessed before supplementation (baseline) using bioelectrical impedance analysis. |
| Iron Status (Iron, Ferritin, UIBC, TIBC) (μg/dL) | Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals). | Serum iron concentration, ferritin concentration, unsaturated iron-binding capacity (UIBC), and total iron-binding capacity (TIBC) will be assessed from fingertip capillary blood collected before supplementation (baseline). |
| Iron Status (Transferrin Concentration) (g/L) | Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals). | Serum transferrin concentration will be assessed from fingertip capillary blood collected before supplementation (baseline). |
| 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). | Subjective sleep quality will be assessed using a Visual Analog Scale (VAS). |
| 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). | Mood state will be assessed using the Brunel Mood Scale (BRUMS). |
| 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). | Competitive state anxiety will be assessed using the Revised Competitive State Anxiety Inventory-2 (CSAI-2R). |
| 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). | Perceived arousal will be assessed using the Felt Arousal Scale (FAS). |
| Feeling Scale (FS; points) | Before supplementation (baseline), pre-exercise, and immediately after exercise at each experimental visit (Visits T1-T4; 7-day intervals). | Affective valence will be assessed using the Feeling Scale (FS). |
Countries
Poland
Contacts
CONTACTNatalia Główka, PhD
PRINCIPAL_INVESTIGATORNatalia Główka, PhD
Poznan University of Physical Education, Department of Sports Dietetics
Outcome results
None listed