This is an 8-week longitudinal double-blind clinical trial type study. The study was approved by the Research Ethics Committee of Hospital of Clínicas in Medical School of Ribeirão Preto – HCFMRP (Universidade de São Paulo – USP); technical opinion n.º 3.089.224).
22 flag football male players participated in this study with age between 19- 24 years old. The sample size was determined by convenience, according to the acceptance and availability of the athletes. As inclusion criteria were adopted: being between 18-25 years old and experience in the sport of, at least, one year. As exclusion criteria: the subjects have been taking any supplementation; took or have been taking any anabolic steroids. All participants received and signed an informed consent form in which they were informed of the structure of the study, and its possible risks and implications.
The participants were randomized through a computer software and divided into two groups, being instructed to ingest a “supplement capsule” 60 minutes before trainings. The content of the provided capsule of each group was unknown for both researcher and athletes. One group received capsules containing 200mg of teacrine (named T) and the other group received placebo capsules containing maltodextrin (placebo). The capsules of the two groups were of the same weight and size. The person in charge for the receiving and distribution of the capsules to the subjects of this study was a responsible for the team, in which, kept the confidentiality of the content in order to preserve the authoritativeness of the research. Participants were evaluated in two distinct moments: the first evaluation was done before the supplementation period (pre); the second evaluation occurred after 8 weeks of supplementation and the training program (post). The evaluations included:
The tests utilized to evaluate the physical performance of the athletes were the following: sextuple jump , T test , 30m sprint , 40-second run test (Matsudo test) , and 12-minute run test (Cooper test) .
Height, body mass, fat mass, and lean mass were determined. For this, a stadiometer (AVA-312, Avanutri, Três Rios, Brazil) and a bioimpedance scale (BF 1000, Beurer, Ulm, Germany) were used. Anthropometric evaluations were performed one day before physical tests, since it was necessary the athletes to be in fasting.
Blood analyzes were performed to determine serum levels of IGF-1 and its binding protein IGFBP-3. Blood samples were collected right after lunch, respecting the interval of, at least, 2 hours after the last meal, by a qualified nurse professional. Venous blood sample was collected by puncture of blood vessel on the anterior forearm. 5 ml blood of each individual were collected in tubes without addition of anticoagulant. The samples were immediately stored at 0-4ºC, then centrifuged between 0 and 4ºC at 1200 rpm for 12 minutes and the blood serum stored at -80ºC for hormonal dosages. There was not storage of biological material in a bank, and the samples were discarded right after the analysis.
Serum levels of IGF-1, IGFBP-3 were determined by specific immunoassays using a commercial kit and expressed in ng/mL (Immulite 2000, Siemens, Los Angeles, CA, USA). All samples of the study were dosed in duplicate within same assay. The intra-assay coefficients of variation were 2.77% for IGF-I; and 2.60% for IGFBP-3. The assays were carried out in the Endocrinology Lab of Hospital of Clínicas in Medical School of Ribeirão Preto (Universidade de São Paulo).
The training of the athletes during the research period was composed by physical preparation (2 weekly session constituted by force training and followed by aerobic work, totalizing about 90 minutes each) on Mondays and Thursdays; also, technical-tactical preparation (on Saturday afternoon and Sunday mornings, in which the athletes perform physical, technical, and tactical training specific of the modality).
Diet and total energy expenditure
The total energy expenditure (TEE), as well as the composition of the diet of the athletes were calculated by a nutritionist of the team. To estimate TEE, it was utilized the Dietary Reference Intakes (DRIs) 2005 . The energetic intake and the division of micro and macronutrients followed the literature recommendations [15,16].
It was utilized a linear model of mixed effects, adopting a significance level of 0,05. The variables are expressed in median and interquartile range and standard deviation, or when indicated and appropriated in mean and standard deviation. After a well detailed description of the data, it was adjusted linear models of mixed effect to compare the means of the group and moments of interest. Multiple comparisons were performed by estimating orthogonal contrasts, obtaining the difference between means and their respective confidence interval of 95%. The data were analyzed by the software SAS (SAS Statistical Software version 9.3; SAS Institute, Inc. Cary, NC). It was utilized PROC MIXED of the software SAS 9.4 (SAS Institute Inc, Cary, NC).