{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,2]],"date-time":"2026-09-02T08:21:10Z","timestamp":1788337270680,"version":"build-2803163510"},"reference-count":28,"publisher":"MDPI AG","issue":"17","license":[{"start":{"date-parts":[[2026,9,2]],"date-time":"2026-09-02T00:00:00Z","timestamp":1788307200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Nutrients"],"abstract":"<jats:p>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 \u00b1 5 years; height: 174 \u00b1 5 cm; BMI: 25.2 \u00b1 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\u2019s d = 0.54) and performance index (p = 0.012; Cohen\u2019s 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 &gt; 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 &gt; 0.05). Salivary \u03b1-amylase concentration was also significantly higher in the CAF trial compared with the CG trial after testing (p = 0.040; Cohen\u2019s 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.<\/jats:p>","DOI":"10.3390\/nu18172876","type":"journal-article","created":{"date-parts":[[2026,9,2]],"date-time":"2026-09-02T07:53:11Z","timestamp":1788335591000},"page":"2876","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Acute Caffeine Administered in Chewing Gum May Improve Functional Firefighting Balance After Gamma-Aminobutyric Acid Supplementation: A Double-Blind Crossover Trial"],"prefix":"10.3390","volume":"18","author":[{"given":"Mei-Hui","family":"Tseng","sequence":"first","affiliation":[{"name":"Institute of Biomedical Sciences, National Chung Hsing University, Taichung 402202, Taiwan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6676-9344","authenticated-orcid":false,"given":"Ching-Lin","family":"Wu","sequence":"additional","affiliation":[{"name":"Graduate Institute of Sports and Health Management, National Chung Hsing University, Taichung 402202, Taiwan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yi-Jie","family":"Shiu","sequence":"additional","affiliation":[{"name":"Physical Education and Sport Sciences, National Taiwan Normal University, Taipei 106308, Taiwan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yi-Chun","family":"Tsou","sequence":"additional","affiliation":[{"name":"Graduate Program in Department of Exercise and Health Science, National Taiwan University of Sport, Taichung 404401, Taiwan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hsien-Tsung","family":"Lin","sequence":"additional","affiliation":[{"name":"Graduate Program in Department of Exercise and Health Science, National Taiwan University of Sport, Taichung 404401, Taiwan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Chih-Hui","family":"Chiu","sequence":"additional","affiliation":[{"name":"Graduate Program in Department of Exercise and Health Science, National Taiwan University of Sport, Taichung 404401, Taiwan"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,9,2]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Williams-Bell, F.M., and CMcGregor, A.M. (2022). Firefighter Personnel and Their Activities in Extreme Environments, in Engineering and Medicine in Extreme Environments, Springer.","DOI":"10.1007\/978-3-030-96921-9_12"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"167","DOI":"10.1080\/10407413.2014.875357","article-title":"Fighting fires without falling: Effects of equipment design and fatigue on firefighter\u2019s balance and gait","volume":"26","author":"Rosengren","year":"2014","journal-title":"Ecol. Psychol."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"1193","DOI":"10.1080\/00140139.2019.1623422","article-title":"The effect of firefighter personal protective equipment on static and dynamic balance","volume":"62","author":"Brown","year":"2019","journal-title":"Ergonomics"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"547","DOI":"10.1007\/s10068-016-0076-9","article-title":"Effect of oral \u03b3-aminobutyric acid (GABA) administration on sleep and its absorption in humans","volume":"25","author":"Yamatsu","year":"2016","journal-title":"Food Sci. Biotechnol."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"8852","DOI":"10.1080\/10408398.2023.2204373","article-title":"Gamma-aminobutyric acid (GABA): A comprehensive review of dietary sources, enrichment technologies, processing effects, health benefits, and its applications","volume":"64","author":"Hou","year":"2024","journal-title":"Crit. Rev. Food Sci. Nutr."},{"key":"ref_6","doi-asserted-by":"crossref","unstructured":"Lim, L.W., and Aquili, L. (2021). GABA supplementation negatively affects cognitive flexibility independent of tyrosine. J. Clin. Med., 10.","DOI":"10.3390\/jcm10091807"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"241","DOI":"10.3390\/nutraceuticals4020015","article-title":"The effect of oral GABA on the nervous system: Potential for therapeutic intervention","volume":"4","author":"Almutairi","year":"2024","journal-title":"Nutraceuticals"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"41","DOI":"10.1007\/s004210050556","article-title":"Autonomic nervous system responses as performance indicators among volleyball players","volume":"80","author":"Collet","year":"1999","journal-title":"Eur. J. Appl. Physiol."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"2414871","DOI":"10.1080\/15502783.2024.2414871","article-title":"Acute ingestion of caffeinated chewing gum reduces fatigue index and improves 400-meter performance in trained sprinters: A double-blind crossover trial","volume":"21","author":"Shiu","year":"2024","journal-title":"J. Int. Soc. Sports Nutr."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"4269","DOI":"10.1007\/s00421-026-06247-0","article-title":"Caffeinated chewing gum improves military performances in special forces soldiers","volume":"126","author":"Shiu","year":"2026","journal-title":"Eur. J. Appl. Physiol."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"41","DOI":"10.1123\/ijspp.2025-0210","article-title":"Caffeinated Chewing Gum Improves Sympathetic Nerve Activity and Wrestling Performance: A Double-Blind Crossover Trial","volume":"21","author":"Tzeng","year":"2026","journal-title":"Int. J. Sports Physiol. Perform."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"569","DOI":"10.1016\/j.jsams.2014.07.017","article-title":"Caffeine and diuresis during rest and exercise: A meta-analysis","volume":"18","author":"Zhang","year":"2015","journal-title":"J. Sci. Med. Sport"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"3293","DOI":"10.1007\/s00394-019-02167-2","article-title":"Time course of tolerance to adverse effects associated with the ingestion of a moderate dose of caffeine","volume":"59","author":"Lara","year":"2020","journal-title":"Eur. J. Nutr."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"175","DOI":"10.3758\/BF03193146","article-title":"G* Power 3: A flexible statistical power analysis program for the social, behavioral, and biomedical sciences","volume":"39","author":"Faul","year":"2007","journal-title":"Behav. Res. Methods"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"159","DOI":"10.1016\/S0378-5173(01)00958-9","article-title":"The rate of absorption and relative bioavailability of caffeine administered in chewing gum versus capsules to normal healthy volunteers","volume":"234","author":"Kamimori","year":"2002","journal-title":"Int. J. Pharm."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"15328","DOI":"10.1038\/s41598-018-33555-z","article-title":"Relationships Between Neuromuscular Function and Functional Balance Performance in Firefighters","volume":"8","author":"Mota","year":"2018","journal-title":"Sci. Rep."},{"key":"ref_17","doi-asserted-by":"crossref","unstructured":"Liu, H.-S., Okada, T., Mitsuya, H., Hsieh, M.-H., Hou, C.-W., Chang, C.-C., and Chiu, C.-H. (2025). Effects of caffeinated chewing gum-induced sympathetic activation and diuretic effect on the rapid rate of weight loss in bodybuilders: A double-blind crossover study. Bmc Sports Sci. Med. Rehabil., 17.","DOI":"10.1186\/s13102-025-01144-z"},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"16","DOI":"10.1186\/s12970-021-00413-9","article-title":"Nicotine supplementation enhances simulated game performance of archery athletes","volume":"18","author":"Hung","year":"2021","journal-title":"J. Int. Soc. Sports Nutr."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"173","DOI":"10.1080\/03091902.2019.1640306","article-title":"A robust algorithm for heart rate variability time series artefact correction using novel beat classification","volume":"43","author":"Lipponen","year":"2019","journal-title":"J. Med. Eng. Technol."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"2074","DOI":"10.1038\/s41598-024-52599-y","article-title":"Caffeine supplementation improves the cognitive abilities and shooting performance of elite e-sports players: A crossover trial","volume":"14","author":"Wu","year":"2024","journal-title":"Sci. Rep."},{"key":"ref_21","doi-asserted-by":"crossref","unstructured":"Liu, H.-S., Liu, C.-C., Shiu, Y.-J., Lan, P.-T., Wang, A.-Y., and Chiu, C.-H. (2024). Caffeinated chewing gum improves basketball shooting accuracy and physical performance indicators of trained basketball players: A double-blind crossover trial. Nutrients, 16.","DOI":"10.3390\/nu16091256"},{"key":"ref_22","unstructured":"Hopkins, W.G. (2009, June 01). A Scale of Magnitudes for Effect Statistics, 2002. Available online: http:\/\/www.sportsci.org\/resource\/stats\/index.html."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1186\/s12970-020-00383-4","article-title":"International society of sports nutrition position stand: Caffeine and exercise performance","volume":"18","author":"Guest","year":"2021","journal-title":"J. Int. Soc. Sports Nutr."},{"key":"ref_24","doi-asserted-by":"crossref","unstructured":"Briggs, I., Chidley, J.B., Chidley, C., and Osler, C.J. (2021). Effects of caffeine ingestion on human standing balance: A systematic review of placebo-controlled trials. Nutrients, 13.","DOI":"10.3390\/nu13103527"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"127","DOI":"10.4103\/0972-6748.62274","article-title":"Hypothesis testing, type I and type II errors","volume":"18","author":"Banerjee","year":"2009","journal-title":"Ind. Psychiatry J."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"605","DOI":"10.1111\/apa.13384","article-title":"Understanding type I and type II errors, statistical power and sample size","volume":"105","author":"Akobeng","year":"2016","journal-title":"Acta Paediatr."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"41","DOI":"10.1089\/jcr.2011.0005","article-title":"Gender differences in subjective and physiological responses to caffeine and the role of steroid hormones","volume":"1","author":"Temple","year":"2011","journal-title":"J. Caffeine Res."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"13795","DOI":"10.1038\/s41598-023-40365-5","article-title":"Acute effects of caffeine supplementation on taekwondo performance: The influence of competition level and sex","volume":"13","author":"Ouergui","year":"2023","journal-title":"Sci. Rep."}],"container-title":["Nutrients"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2072-6643\/18\/17\/2876\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,9,2]],"date-time":"2026-09-02T07:59:23Z","timestamp":1788335963000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2072-6643\/18\/17\/2876"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,9,2]]},"references-count":28,"journal-issue":{"issue":"17","published-online":{"date-parts":[[2026,9]]}},"alternative-id":["nu18172876"],"URL":"https:\/\/doi.org\/10.3390\/nu18172876","relation":{},"ISSN":["2072-6643"],"issn-type":[{"value":"2072-6643","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,9,2]]}}}