Effects of β-Alanine Supplementation on Kickboxing-Specific Anaerobic Performance, Neuromuscular Power, and Strength Endurance: A Randomized, Double-Blind, Placebo-Controlled Trial

Rationale and Background: β-Alanine supplementation increases intramuscular carnosine, enhancing intracellular buffering capacity and potentially preserving excitation-contraction coupling during high-intensity, repeated efforts. Kickboxing competition is characterized by short striking bouts, rapid direction changes, and high glycolytic contribution-conditions under which increased buffering may translate to meaningful performance benefits. Prior work in combat sports has reported ergogenic effects of BA; however, evidence in kickboxing using a validated sport-specific test remains limited. This trial addresses that gap using the Kickboxing Anaerobic Speed Test (KAST), which offers strong ecological validity for combat athletes.

Design and Setting: Randomized, double-blind, placebo-controlled, parallel-group clinical trial with two assessment time points (pre, post). Participants continue usual training under coach supervision and are instructed to avoid other ergogenic aids and caffeine for 24 h before testing. All testing is performed under standardized environmental conditions (temperature and humidity controlled) and at the same time of day (±1 h) to minimize circadian and residual fatigue effects.

Participants: Twenty-eight healthy adult male kickboxers with ≥5 years of systematic training and active competition in the prior year. Key exclusions include musculoskeletal injury limiting high-intensity exercise, cardiometabolic or respiratory disease, β-alanine intolerance, and recent use of overlapping supplements. Written informed consent is obtained. The protocol complies with the Declaration of Helsinki and local ethics approval.

Interventions Experimental: β-alanine, 6.4 g·day-¹ for 4 weeks (e.g., divided doses). Comparator: Appearance-matched placebo (rice flour), same schedule. Products are dispensed in coded containers to preserve blinding of participants, investigators, and outcome assessors.

Outcome Measures Primary: KASTtotal (s), computed as the sum of five consecutive sets of a standardized four-technique combination performed at maximal effort with 10-s passive recovery. Timing starts at first bag contact and ends after the final kick; performance is video-recorded at 25 fps and analyzed frame-by-frame.

Secondary: KASTbest (best of two maximal sets separated by 5-min recovery), individual set times KAST₁-₅, PDI (%) = KASTtotal/(KASTbest × 5) × 100, CMJ and SJ height (hands on hips; validated smartphone app), and maximal push-ups and pull-ups (strict form criteria). Adverse events and tolerability-especially paresthesia-are recorded throughout.

Procedures and Standardization: A familiarization session precedes baseline testing. Warm-up includes light aerobic activity, dynamic drills, plyometrics, mobility work, and shadowboxing following a scripted sequence. Standardized verbal encouragement and rest intervals are used. Technique order for KAST is fixed; any deviation leads to trial termination and repeat after enforced rest.

Sample Size and Statistical Analysis: An a priori power analysis for a medium within-between interaction (α=0.05, power 0.80) indicated a minimum sample of 24; the target enrollment of 28 provides adequate sensitivity. Baseline between-group differences are assessed by independent t-tests (effect size: Hedges' g). The primary inferential model is a two-way repeated-measures ANOVA (group × time) for each outcome, reporting F(1,26), p values, and partial eta-squared (ηp²) with conventional magnitude thresholds. Assumptions are tested (Shapiro-Wilk, Levene, Mauchly); Greenhouse-Geisser corrections are applied as needed. When interactions are significant, simple-effects tests with Bonferroni adjustment localize differences.

Safety and Monitoring: This is a low-risk nutrition study in trained athletes. The most common expected adverse effect is transient paresthesia, which will be monitored via spontaneous reports and direct questioning. Any unexpected or serious events will be evaluated and reported per institutional policy; supplementation may be paused or discontinued at investigator discretion.

Expected Impact and Limitations: BA to reduce KASTtotal and improve push-up and pull-up performance versus placebo, with minimal changes in CMJ/SJ. Limitations include the absence of direct physiological verification of carnosine accrual (e.g., muscle biopsy) and lack of concurrent lactate or pH measures, which constrain mechanistic inference. Nonetheless, by deploying a validated, sport-specific performance test with rigorous control of confounders and blinded assessment, this trial aims to provide clinically relevant, ecologically valid evidence for practitioners working with combat sport athletes.