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Abstract
Background
Caffeine (CAF) has been shown to improve performance during early phase of repeated sprint exercise; however some studies show that CAF also increases the magnitude of physical stress represented by augmented blood lactate, glucose, and cortisol concentrations during latter phase of repeated sprint exercise. No studies have investigated the efficacy of combined carbohydrate (CHO) and CAF consumption during repeated sprint exercise (RSE) in female athletes. Thus, the purpose of this study was to investigate the effects of CAF with CHO supplementation on RSE and agility.
Methods
Eleven female athletes completed four experimental trials performed 7 d apart in a double-blind, randomized, and counter-balanced crossover design. Treatments included CAF + PLA (placebo), CAF + CHO, PLA + CHO, and PLA + PLA. Participants ingested capsules containing 6 mg · kg−1 of CAF or PLA 60-min prior to RSE, and 0.8 g · kg−1 of CHO solution or PLA immediately before the RSE, which consisted of ten sets of 5 × 4-s sprints on the cycle ergometer with 20-s active recovery. The agility T-test (AT-test) was performed before and after the RSE. Blood samples were acquired to assess glucose, lactate, testosterone, and cortisol.
Results
During Set 6 of RSE, peak power and mean power were significantly higher in PLA + CHO than those in CAF + PLA and PLA + PLA, respectively (p < .05). Total work was significantly increased by 4.8% and 5.9% with PLA + CHO than those of CAF + CHO and CAF + PLA during Set 3. PLA + CHO also increased total work more than CAF + PLA and PLA + PLA did during Set 6 (p < .05). No significant differences in AT-test performance either before or after the RSE were occurred among treatments (p > .05). Blood lactate and glucose concentrations were significantly higher under CAF + CHO, CAF + PLA, and PLA + CHO versus PLA + PLA (p < .05), but no differences in testosterone or cortisol levels were found (p > .05).
Conclusions
Findings indicate that CAF + PLA or CAF + CHO ingestion did not improve repeated sprint performance with short rest intervals or agility. However, CHO ingested immediately prior to exercise provided a small but significant benefit on RSE performance in female athletes.
Electronic supplementary material
The online version of this article (doi:10.1186/1550-2783-11-17) contains supplementary material, which is available to authorized users.
Copyright comment
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Electronic supplementary material
The online version of this article (doi:10.1186/1550-2783-11-17) contains supplementary material, which is available to authorized users.
Copyright comment
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Acknowledgements
We would like to thank all participants and research assistants for their effort in the study. This work was partly supported by a research grant from the Ministry of Science and Technology, Taiwan (NSC 101–2410-H-110–085). This work was also particularly supported by “Aim for the Top University Plan” of National Taiwan Normal University , National Sun Yat-sen University, and the Ministry of Education, Taiwan.
Competing interests
The authors declare that they have no competing of interest.
Authors’ contributions
CLL and CFC developed the study design, data collection, statistical analysis, and all sport drink tested. TA helped draft the manuscript. JCL was in charge of participant recruitment and management. HWH contributed to the data collection and analysis. WDC provided consultation. All authors contributed to drafting of the manuscript. All authors have read and approved the final manuscript.