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

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.

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.