2.2. Procedures
RPE, cognitive interference [
A crossover randomized double-blind placebo-controlled trial was used in the current study. Two weeks after the familiarization session, participants performed an SSG exercise protocol after the ingestion of caffeine (5 mg.kgTesting sessions were performed at the same time of the day (08 am) to avoid variations in the circadian cycle. Environmental conditions were: (a) temperature (°C): start: 31.9 ± 1.98, end: 32.45 ± 3.21; (b) relative air humidity (%): start: 51.85 ± 5.31, end: 51.3 ± 5.36; (c) wind speed (m/s): start: 4.35 ± 4.46, end: 3.08 ± 5.91. These variables were measured using a digital thermo-higro-anemometer (Akrom KR825, São Leopoldo-RS, Brazil).The SSG was composed of a GK + 3 × 3 + GK format (3 players + goalkeeper on each team) with a constant area of 36 m × 27 m and 5 min duration. After 5 min of warm-up, five series of SSG were performed, with 1 min of recovery between each SSG. Team formations and experimental conditions (caffeine and placebo) were randomized. Each team consisted of a goalkeeper (not used in the analysis), a defender, a midfielder and a forward. The team formation was the same for both experimental trials and all players of each team were under the same condition (caffeine or placebo). No specific verbal instructions were provided before, during, or after the SSGs, which followed official soccer rules, including offside. Water was consumed ad libidum for hydration. The objective of each game was to score and outscore the opponents. Ratings of perceived exertion (RPE) were assessed after each SSG using a 0–10 scale (from “no exertion at all” to “maximal effort”) [Caffeine ingestion: 45 min before testing, participants ingested 5 mg.kgStroop test: the computerized colour Stroop test consists of the visualization of coloured words on the computer screen (i.e., red, blue, yellow, and green) and the identification of the correct colour using the corresponding keyboard key, which were painted in the respective colour. Participants were asked to select the correct colour of the word, not the word itself, as quickly as possible. Words appeared on the computer screen in three different ways: (i) neutral words (neutral condition); (ii) correspondent colour (i.e., “red” painted in red; congruent condition), or; (iii) different colour (i.e., “red” painted in green; incongruent condition). The incongruent condition aimed to cause the interference effect, as the colour and the word did not match. The Stroop test is a valid tool to assess selective attention and the ability to inhibit cognitive interference [