Acute Caffeine Administered in Chewing Gum May Improve Functional Firefighting Balance After Gamma-Aminobutyric Acid Supplementation: A Double-Blind Crossover Trial.

BACKGROUND: This study investigated whether caffeinated chewing gum enhances sympathetic activity and improves functional firefighting balance performance after gamma-aminobutyric acid (GABA) supplementation. METHODS: Fourteen active-duty elite firefighters (age: 36 ± 5 years; height: 174 ± 5 cm; BMI: 25.2 ± 1.6 kg/m2) participated in a double-blind randomized crossover trial. The participants completed functional firefighting balance tests while wearing approximately 25 kg of full firefighting gear. After a 1 h resting period, the participants ingested GABA and rested for an additional 15 min before chewing either caffeine-containing gum (CAF) or caffeine-free gum (CG) for 10 min. Fifteen minutes after gum ingestion, the participants repeated the functional firefighting balance tests. Completion time and performance index were used as the indicators of the functional firefighting balance tests. RESULTS: The CAF trial demonstrated a significantly better completion time (p = 0.011; Cohen's d = 0.54) and performance index (p = 0.012; Cohen's d = 0.43) compared with the CG trial, with small-to-moderate effect sizes. There were no significant interactions in HR, SDNN, RMSSD, LF and HF (condition*time, p > 0.05). There was a significant interaction in LF/HF (p = 0.040); however, further statistical analysis revealed no significant differences across trials or over time (p > 0.05). Salivary α-amylase concentration was also significantly higher in the CAF trial compared with the CG trial after testing (p = 0.040; Cohen's d = 0.45). CONCLUSIONS: These findings suggest that caffeinated chewing gum may enhance functional balance performance with a small effect size after GABA supplementation. The increased activity of the sympathetic nervous system may be one of the reasons for improved functional firefighting balance performance.