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The primary aim of this study was to compare the measured oxygen consumption (Measured -V O 2 ) in a simulated futsal game (S-Game) with the estimated oxygen consumption (Estimated -V O 2 ) through a regression equation between heart rate (HR) and oxygen consumption ( V O 2 ) (HR- V O 2 ) in treadmill running, and a secondary aim was to calculate the total energy expenditure (EE) in S-Game. Ten professional players (22.20 ± 3.22 years) were evaluated. HR- V O 2 was determined individually in the continuous test on the treadmill (Cont Test ). The Measured -V O 2 in S-Game was compared with the Estimated -V O 2 in the Cont Test . Alactic and lactic pathways were estimated by V O 2 . The Estimated -V O 2 presented no statistically significant difference with the Measured -V O 2 , using the paired t -test ( p = 0.38). However, the correlation between Estimated- and Measured- V O 2 was very weak ( r = -0.05), and it presented poor agreement (concordance correlation coefficient = -0.04). In addition, a Bland-Altman plot presented bias of -2.8 ml/kg/min and individual difference as large as 19 ml/kg/min. The HR- V O 2 determined by the Cont Test was not a good individual predictor of V O 2 . The high intensity and intermittent nature of the futsal game possibly caused dissociation in the HR- V O 2 relationship. Cont Test is not recommended for estimating V O 2 and calculating individual EE in the futsal game. This is recommended only for the group mean. The total EE in S-Game was 13.10 ± 1.25 kcal.min -1 (10.81 ± 1.57 metabolic equivalents). The contributions from the metabolic pathways were as follows: aerobic (93%), alactic (5%), and lactic (2%)., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Silva, Nakamura, Papoti, da Silva and Dos-Santos.)

Physiological responses in futsal have not been studied together with temporal information about the players' stay on the court. The aim of this study was to compare heart rate (HR) and blood lactate concentration ([La - ]) responses between 1-H and 2-H considering the time of permanency of the players on the court at each substitution in a futsal match. HR was recorded during entire match and [La - ] was analyzed after each substitution of seven players. %HR mean (89.61 ± 2.31 vs. 88.03 ± 4.98 %HR max ) and [La - ] mean (8.46 ± 3.01 vs. 8.17 ± 2.91 mmol·L -1 ) did not differ between 1-H and 2-H (ES, trivial-small). Time in intensity zones of 50-100 %HR max differed only in 60-70 %HR max (ES, moderate). HR coefficient of variation throughout the match was low (7%) and among the four outfield players on the court (quartets, 5%). Substitutions (2 player's participation in each half), time of permanence on the court (7.15 ± 2.39 vs. 9.49 ± 3.80 min), ratio between time in- and out-ratio on the court (In:Outcourt = 1:1.30 ± 1:0.48 vs. 1:1.05 ± 1:0.55 min) also were similar between 1-H and 2-H (ES, moderate and small, respectively). Balancing the number of substitutions, and the In:Outcourt ratio of players in both halves of the match, playing lower time at 1-H, ~8 min for each participation in the match, made it possible to maintain intensity of the match in 2-H similar to the 1H. These results are a good guidance to coaches and for application in future studies., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2020 Dos-Santos, da Silva, da Silva Junior, Barbieri, Penafiel, da Silva, Milioni, Vieira, Coledam, Santiago and Papoti.)