The Effects of Acute Nitrate and Caffeine Co-ingestion on Discipline-Specific Exercise Performance.

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.

Overview

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 supplement Caffeine
  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
• Dietary supplement 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 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 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.

Primary outcome measures

• 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).]
• 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).]

Secondary outcome measures (12)

• 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).]

Eligibility criteria

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.

Criteria are shown verbatim from the registry (in English). Final eligibility is always assessed by the study center.

Healthy volunteers: Yes

Study design

Allocation

Randomized

Model

Crossover

Masking

Quadruple blind

Primary purpose

Basic science

Study locations

Poland · 1 center

• Poznan University of Physical Education — Poznan

Identifiers

NCT: NCT07748416 · ZDS2026_NG_001

Primary sources (government registries)

• ClinicalTrials.gov (US NIH)

View this study on ClinicalTrials.gov ↗