Athletic PerformanceNCT07748416
The Effects of Acute Nitrate and Caffeine Co-ingestion on Discipline-Specific Exercise Performance.
A study testing Caffeine and Dietary Nitrate (Beetroot Juice) in people with Athletic Performance and Dietary Supplement, run by Poznan University of Physical Education at 1 site in Poland.
Trial 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. Read more about this study
- Who is it for?
- Ages 16 to 45 yearsHealthy volunteers can take part
- Conditions the study is for
- Athletic Performance, Dietary Supplement, Iron Status
- What is being tested?
- Caffeine and Dietary Nitrate (Beetroot Juice)
- Type of treatment
- Pill or oral medicine
- Could I receive a placebo?
- Yes, some participants may receive a placebo
- How many people
- 112 participants
- Where
- 1 sitePoland
- Study dates
- 1 Oct 2026to 30 Jun 2029
- Phase
- Interventional
- Are there results?
- Not yet: the study is under way
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 16 to 45 years
- All sexes
- Healthy volunteers accepted
- Child, Adult
Who may be able to join
- 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.
Show all 19Show fewer
- 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.
Who cannot join
- 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.
Trial locations and contacts
1 site in 1 country. Contact the study team or a site near you to ask about taking part.
Poland1 site
Poznan University of Physical Education
Poznan, Wielkopolska, 61-871
Natalia Główka, 691756944, glowka@awf.poznan.pl
About this study
Official title: 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.
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.
Read the 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.
- Conditions
- Athletic Performance, Dietary Supplement, Iron Status
- Being tested
- Caffeine, Dietary Nitrate (Beetroot Juice), Placebo (Maltodextrin Capsule), Placebo (Nitrate-Depleted Beetroot Juice)
- Keywords
- Caffeine, Sports nutrition, Swimming, High-Intensity Functional Training, Nitric oxide
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
CaffeineDietary supplement
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 Nitrate (Beetroot Juice)Dietary supplement
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.
Placebo (Maltodextrin Capsule)Dietary supplement
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).
Placebo (Nitrate-Depleted Beetroot Juice)Dietary supplement
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.
| Study group | Role | What they receive |
|---|---|---|
| CAF + BJ (Active Co-ingestion) | Experimental | 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. Receives: Dietary Supplement: Caffeine; Dietary Supplement: Dietary Nitrate (Beetroot Juice) |
| CAF + PLBJ (Caffeine + Placebo BJ) | Active comparator | 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. Receives: Dietary Supplement: Caffeine; Dietary Supplement: Placebo (Nitrate-Depleted Beetroot Juice) |
| PLCAF + BJ (Placebo CAF + Beetroot Juice) | Active comparator | 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. Receives: Dietary Supplement: Dietary Nitrate (Beetroot Juice); Dietary Supplement: Placebo (Maltodextrin Capsule) |
| PLCAF + PLBJ (Double Placebo Control) | Placebo comparator | 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. Receives: Dietary Supplement: Placebo (Maltodextrin Capsule); Dietary Supplement: Placebo (Nitrate-Depleted Beetroot Juice) |
What is being measured
The primary outcome is the main question the study is designed to answer.
Exercise Performance Time (minutes and seconds, Cohort A - Hyrox P'F'T)
Total time (in minutes and seconds) required to complete the standardized HYROX Physical Fitness Test (P'F'T) consisting of 6 specific functional exercises.
Measured: At each experimental visit (Visits T1-T4), with visits conducted at 7-day intervals following the baseline/familiarization visit (T0).
Swimming Performance (minutes and seconds, Cohort B - 8x100m Step-Test)
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.
Measured: At each experimental visit (Visits T1-T4), with visits conducted at 7-day intervals following the baseline/familiarization visit (T0).
Secondary outcomes (31)
Blood Lactate Kinetics (mmol/L)
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.
Measured: 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)
Real-time heart rate (beats per minute) will be continuously monitored throughout each exercise test using a telemetry-based heart rate monitoring system.
Measured: Continuously monitored during exercise at each experimental visit (Visits T1-T4; 7-day intervals).
Rating of Perceived Exertion (RPE, points)
Subjective rating of perceived exertion will be assessed using the validated Borg Scale (6-20).
Measured: Immediately after exercise at each experimental visit (Visits T1-T4; 7-day intervals).
Blood Pressure (mmHg)
Systolic and diastolic blood pressure will be measured using an automated oscillometric blood pressure monitor.
Measured: 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)
Gastrointestinal symptoms will be assessed using the modified Visual Analog Scale (mVAS; 0-10, where 0 = no symptoms and 10 = extremely severe symptoms).
Measured: 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)
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.
Measured: Before supplementation (baseline) and 3 minutes after exercise at each experimental visit (Visits T1-T4; 7-day intervals).
White blood cells count and differential (%)
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.
Measured: 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)
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.
Measured: 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)
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.
Measured: Before supplementation (baseline) and 3 minutes after exercise at each experimental visit (Visits T1-T4; 7-day intervals).
Hematological indices (hematocrit, HCT) (L/L)
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.
Measured: 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)
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.
Measured: 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)
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.
Measured: 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)
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.
Measured: 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)
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.
Measured: 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)
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.
Measured: 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) (%)
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.
Measured: 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)
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.
Measured: 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)
Urea concentration will be assessed from fingertip capillary blood collected before supplementation (baseline).
Measured: Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals).
Creatinine Concentration (μmol/L)
Creatinine concentration will be assessed from fingertip capillary blood collected before supplementation (baseline).
Measured: Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals).
Muscle Damage Markers (ALT, AST, CK, LDH) (U/L)
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).
Measured: Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals).
Body composition (fat-free mass, fat mass) (kg)
Body composition will be assessed before supplementation (baseline) using bioelectrical impedance analysis.
Measured: Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals).
Body composition (fat-free mass, fat mass) (%)
Body composition will be assessed before supplementation (baseline) using bioelectrical impedance analysis.
Measured: Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals).
Body composition (total body water) (L)
Body composition will be assessed before supplementation (baseline) using bioelectrical impedance analysis.
Measured: Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals).
Body composition (total body water) (%)
Body composition will be assessed before supplementation (baseline) using bioelectrical impedance analysis.
Measured: Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals).
Iron Status (Iron, Ferritin, UIBC, TIBC) (μg/dL)
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).
Measured: Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals).
Iron Status (Transferrin Concentration) (g/L)
Serum transferrin concentration will be assessed from fingertip capillary blood collected before supplementation (baseline).
Measured: Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals).
Sleep Quality (Visual Analog Scale, VAS; points)
Subjective sleep quality will be assessed using a Visual Analog Scale (VAS).
Measured: 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)
Mood state will be assessed using the Brunel Mood Scale (BRUMS).
Measured: 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)
Competitive state anxiety will be assessed using the Revised Competitive State Anxiety Inventory-2 (CSAI-2R).
Measured: 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)
Perceived arousal will be assessed using the Felt Arousal Scale (FAS).
Measured: Before supplementation (baseline), pre-exercise, and immediately after exercise at each experimental visit (Visits T1-T4; 7-day intervals).
Feeling Scale (FS; points)
Affective valence will be assessed using the Feeling Scale (FS).
Measured: Before supplementation (baseline), pre-exercise, and immediately after exercise at each experimental visit (Visits T1-T4; 7-day intervals).
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted5 Aug 2026
- Study start1 Oct 2026 (estimated)
- Primary completion30 Jun 2029 (estimated)
- Study completion30 Jun 2029 (estimated)
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Other trials for Athletic PerformanceStudies of the same condition, open and under way.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase N/A
- Primary purpose
- Basic science
- Allocation
- Randomised
- Intervention model
- Crossover
- 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).
- Masking
- Quadruple blind
- Who is masked
- Participant, Care provider, Investigator, Outcomes assessor
- Enrolment
- 112 participants (estimated)
Sponsor and investigators
- Lead sponsor
- Poznan University of Physical Education
- Sponsor type
- University, hospital or other
- Responsible party
- Sponsor
- Investigators
- Natalia Główka, PhD, Principal investigator, Poznan University of Physical Education, Department of Sports Dietetics
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT07748416
- Sponsor's protocol ID
- ZDS2026_NG_001
- Status last verified
- Jul 2026
- First submitted
- 17 Jul 2026
- Last updated
- 7 Aug 2026
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- Yes: The study protocol will be published as an open-access article. Upon completion of the study, de-identified individual participant data (IPD) and relevant analytic code will be deposited in an open-access repository such as Zenodo or OSF, following the FAIR principles.
Study at a glance
From the registry record, last updated by the sponsor on 7 Aug 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- 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.
- ClinicalTrials.gov ID
- NCT07748416
- Acronym / sponsor ID
- ZDS2026_NG_001
- Conditions
- Athletic Performance, Dietary Supplement, Iron Status
- Keywords
- Caffeine, Sports nutrition, Swimming, High-Intensity Functional Training, Nitric oxide
- Study type
- Interventional
- Recruitment status
- Not yet recruiting
- Enrolment
- 112 participants (estimated)
- Lead sponsor
- Poznan University of Physical EducationUniversity, hospital or other
- Study start
- 1 Oct 2026 (estimated)
- Primary completion
- 30 Jun 2029 (estimated)
- Study completion
- 30 Jun 2029 (estimated)
- First posted
- 5 Aug 2026 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
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
- Primary purpose
- Basic science
- Allocation
- Randomised
- Intervention model
- Crossover
- Masking
- Quadruple blind (participant, care provider, investigator, outcomes assessor)
- Number of arms
- 4
- 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).
| Arm | Type | Receives |
|---|---|---|
| CAF + BJ (Active Co-ingestion) | Experimental | Dietary Supplement: Caffeine, Dietary Supplement: Dietary Nitrate (Beetroot Juice)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. |
| CAF + PLBJ (Caffeine + Placebo BJ) | Active comparator | Dietary Supplement: Caffeine, Dietary Supplement: Placebo (Nitrate-Depleted Beetroot Juice)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. |
| PLCAF + BJ (Placebo CAF + Beetroot Juice) | Active comparator | Dietary Supplement: Dietary Nitrate (Beetroot Juice), Dietary Supplement: Placebo (Maltodextrin Capsule)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. |
| PLCAF + PLBJ (Double Placebo Control) | Placebo comparator | Dietary Supplement: Placebo (Maltodextrin Capsule), Dietary Supplement: Placebo (Nitrate-Depleted Beetroot Juice)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. |
Who may qualify
- Ages
- 16 to 45 years
- Sex
- All
- Healthy volunteers
- Accepted
- Age groups
- Child, Adult
Key inclusion criteria (19 listed)
- 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.
Key exclusion criteria (3 listed)
- 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.
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| CaffeineAnhydrous 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 supplement | CAF + BJ (Active Co-ingestion), CAF + PLBJ (Caffeine + Placebo BJ) |
| Dietary 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 supplement | CAF + BJ (Active Co-ingestion), PLCAF + BJ (Placebo CAF + Beetroot Juice) |
| Placebo (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 supplement | PLCAF + BJ (Placebo CAF + Beetroot Juice), PLCAF + PLBJ (Double Placebo Control) |
| Placebo (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. | Dietary supplement | CAF + PLBJ (Caffeine + Placebo BJ), PLCAF + PLBJ (Double Placebo Control) |
Primary outcome
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.
31 secondary outcomes
Blood Lactate Kinetics (mmol/L)
Time frame: 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)
Time frame: Continuously monitored during exercise at each experimental visit (Visits T1-T4; 7-day intervals).
Rating of Perceived Exertion (RPE, points)
Time frame: Immediately after exercise at each experimental visit (Visits T1-T4; 7-day intervals).
Blood Pressure (mmHg)
Time frame: 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)
Time frame: 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)
Time frame: Before supplementation (baseline) and 3 minutes after exercise at each experimental visit (Visits T1-T4; 7-day intervals).
White blood cells count and differential (%)
Time frame: 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)
Time frame: 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)
Time frame: Before supplementation (baseline) and 3 minutes after exercise at each experimental visit (Visits T1-T4; 7-day intervals).
Hematological indices (hematocrit, HCT) (L/L)
Time frame: 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)
Time frame: 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)
Time frame: 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)
Time frame: 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)
Time frame: 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)
Time frame: 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) (%)
Time frame: 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)
Time frame: 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)
Time frame: Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals).
Creatinine Concentration (μmol/L)
Time frame: Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals).
Muscle Damage Markers (ALT, AST, CK, LDH) (U/L)
Time frame: Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals).
Body composition (fat-free mass, fat mass) (kg)
Time frame: Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals).
Body composition (fat-free mass, fat mass) (%)
Time frame: Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals).
Body composition (total body water) (L)
Time frame: Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals).
Body composition (total body water) (%)
Time frame: Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals).
Iron Status (Iron, Ferritin, UIBC, TIBC) (μg/dL)
Time frame: Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals).
Iron Status (Transferrin Concentration) (g/L)
Time frame: Before supplementation (baseline) at each experimental visit (Visits T1-T4; 7-day intervals).
Sleep Quality (Visual Analog Scale, VAS; points)
Time frame: 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)
Time frame: 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)
Time frame: 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)
Time frame: Before supplementation (baseline), pre-exercise, and immediately after exercise at each experimental visit (Visits T1-T4; 7-day intervals).
Feeling Scale (FS; points)
Time frame: Before supplementation (baseline), pre-exercise, and immediately after exercise at each experimental visit (Visits T1-T4; 7-day intervals).
Results and safety
This study is still under way. Results are not available in the source record yet.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 7 Aug 2026.
- Individual participant dataSharing planned: Yes. The study protocol will be published as an open-access article. Upon completion of the study, de-identified individual participant data (IPD) and relevant analytic code will be deposited in an open-access repository such as Zenodo or OSF, following the FAIR principles.
Related trials for Athletic Performance
Recruiting
Acute Effects of Post-Exercise Hyperoxia on Recovery in Cycling
Athletic Performance, Hyperbaric Oxygenation
Not yet recruiting
Core Strength Training, Anthropometry, and Postural Control in Youth Optimist Sailors
Postural Control, Athletic Performance
Active, not recruiting
Effects of Blood Flow Restriction Training on Physical Function, Muscle Adaptations, and Performance in Roller Skaters
Athletic Performance Enhancement
Recruiting
UCLA Magnesium Formulation Athlete Study
Athletic Performance, Recovery
Not yet recruiting
Delayed Morning Training, Sleep, and Change-of-Direction Performance in Badminton Athletes
Sleep Duration, Athletic Performance
Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part.
Natalia Główka, PhD principal investigator
Poznan University of Physical Education, Department of Sports Dietetics
1 site in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A study testing Caffeine and Dietary Nitrate (Beetroot Juice) in people with Athletic Performance and Dietary Supplement, run by Poznan University of Physical Education at 1 site in Poland.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 19 inclusion and 3 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: opening soon, as of the sponsor's last update on 7 Aug 2026. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 1 site in Poland. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. Some participants in this study may receive a placebo. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
Are results available for this study?
This study is still under way. Results are not available in the source record yet.
How can a doctor refer a patient or contact the research team?
Contact Natalia Główka, PhD (+48691756944, glowka@awf.poznan.pl), or a site near the patient. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
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).). The study lists 2 primary outcomes in all. It is what the study was designed to measure, not a finding.
Where can I read the original study information?
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 7 Aug 2026; AzTrials last refreshed its copy on 7 Nov 2026.