COMPARISON OF AEROBIC PERFORMANCE INDICATORS OF SOCCER AND FUTSAL ATHLETES

Soccer and futsal have similar technical movements that are used within different spatial dimensions and game dynamics. The possible physiological differences between players of each sport were unknown. The main purpose of this study was to compare the maximum oxygen uptake (VO 2 max) and ventilatory thresholds (VT) of soccer and futsal players. VO 2 max and VT of 32 athletes (soccer: n = 15; futsal: n = 17) were obtained by ergospirometry in a progressive treadmill test. VO 2 max was similar between groups. VT occurred later and at higher running speeds in the soccer players. The similarities found in VO 2 max may be related to the fact that the evaluations were carried out in the pre-season. The fact that the VT was reached later in the soccer players suggests a longer capacity for aerobic exercise and greater resistance to lactate production. Moreover, soccer players appear to be conditioned to withstand increased running times and speeds, until exhaustion. Players of both sports reached the second VT at similar intensities, suggesting no prevalence of anaerobic metabolism. Soccer and futsal players have similar VO 2 max, but their VTs occur at different times, and at different running speeds. Level of Evidence III; Cross-sectional study.


INTRODUCTION
Soccer is a field sport with various movements and movement patterns required from players (e.g. shorts and long sprints, walking and running slowly, accelerations with rapid decelerations, changes in direction, jumps, kicks, and confrontations). 1,2 Futsal is similar to soccer, but it is played on a smaller court, with fewer players, uses a smaller ball, and allows for constant and unlimited substitutions. [3][4][5][6] Futsal is a dynamic and intense sport that requires many movements within short periods. 3,5,7 Various studies have compared the physiological characteristics of soccer and futsal players. 5,[7][8][9][10][11] Maximum oxygen uptake (VO 2 max) and ventilatory threshold (VT) are two characteristics that are commonly used to measure athletes' fitness. VO 2 max is an indicator of the highest oxygen uptake (VO 2 ) per unit of time that an individual can capture, transport and use at the cellular level. 8 VT is an indicator of lactate production and includes a first and second threshold. 12 VO 2 max is a determinant factor for aerobic capacity 13 and is considered the gold standard for assessing aerobic fitness. VO 2 max seems to be a determinant in soccer performance, 13,14 but not as much in futsal performance. 5 The literature contains contradictory data, where studies have found higher VO 2 max in soccer, 7 or futsal players, 5 and have also observed similarities. 8,10 These different outcomes can be attributed to factors ranging from different evaluation periods during the season, level of competitiveness and evaluation protocols.
VT is a measure of endurance performance. The first VT threshold (VT 1 ) corresponds to the start of blood lactate accumulation, and the second threshold (VT 2 ) to the moment when lactate production exceeds its removal. 9 Studies comparing VTs of soccer and futsal players 5,8-10 have related VT to VO 2 at the time of VT 2 , 5,9 and the percentage of VO 2 max during VT 2 (%VO 2 maxVT 2 ). 9,15 Soccer players reached %VO 2 maxVT 2 between 76.6 and 90.3% and futsal players between 65 and 77%, 9 demonstrating that VT 2 occurred at different exercise intensities. 10 The percentage of VO 2 max during VT 1 (%VO 2 maxVT 1 ) is rarely reported in the literature 16,17 even though it is an indicator of aerobic metabolism 16 that marks the beginning of lactate accumulation. 18 Running speed during each VT is also a parameter of exercise intensity 9,18 , and when running speed is associated with VO 2 max and VT it can provide more information than isolated cardiorespiratory variables. 11,15,19 Studies evaluating running speed during VT 1 (speedVT 1 ), 9 and VT 2 (speedVT 2 ) 5,8,9 have found contradictory results, where: speedVT 1 was superior in futsal players; 9 speedVT 2 was superior in soccer players, and; 8 speedVT 2 was similar in soccer and futsal players. 9 These contradictory outcomes could result from a lack of control in training stage between soccer and futsal players. This study aimed to compare the VO 2 max and VT of soccer and futsal players at the same training stage during the start of the preseason. We hypothesized that: 1) soccer players would have higher VO 2 max than futsal players; 7 and 2) VT 1 and VT 2 would occur earlier in futsal players than soccer players. 9

Participants
This study was approved by the institutional Research Ethics Committee of the University of Santa Cruz do Sul, RS, Brazil (number 1.514.711). All participants read and signed an informed consent form.
Study participants were State level male soccer and futsal players who met the inclusion criteria: a) aged 18 to 30 years old; b) no musculoskeletal injuries; c) no respiratory disorders; and d) no heart disease. Individuals who did not reach VT 2 during testing and those who had difficulties understanding the experimental protocol were excluded from the study. Thirty-two athletes (soccer: n = 15; futsal: n = 17) participated in the study.
The evaluation took place preseason, prior to any soccer or futsal training. During the evaluation period, soccer and futsal players began their preparation to compete in the State championships.
To characterize athletes, body mass and height were measured. Measurements followed Heyward's guidelines using a beam scale (Welmy R110; Welmy SA, Santa Bárbara do Oeste, Brazil). 20

Assessment of performance indicators
Cardiorespiratory parameters were obtained by ergospirometry during a maximal effort test on a treadmill (Super ATL, Inbramed Ltda., Porto Alegre, RS, Brazil). The Bruce ramp protocol was used, which consists of seven three-minute stages. The starting speed and inclination were 2.7 km/h and 10º, respectively. Each progressive stage involved an increase in speed and inclination of 1.6 km/h and 2º. 21,22 Respiratory gases were measured every 20 seconds by a gas analyzer (VO2000, Aerosport, Medgraphics, St. Paul, Minnesota, USA), which was calibrated before the start of each test within a temperature-controlled environment (20-22ºC). Assessments were performed during the day, with all subjects in a resting state (sitting for five minutes) until the time of the test. The test duration was determined by the athletes' voluntary exhaustion; when the athletes reached their effort limit, the test was immediately interrupted, and the recovery phase began [three minutes of walking on the treadmill at 2.7 km/h without any inclination (0º)]. VO 2 max was determined by the VO 2 peak reached during the maximal effort test. 23 It was captured in absolute and relative values, but only relative values were reported. VTs were identified by three experienced evaluators using the visual-graphic method, which consists of observing the behaviour of the VO 2 curve (oxygen consumption over time) and the production of carbon dioxide (VCO 2 ) during progressive effort. VT 1 was identified when the VCO 2 increased disproportionately to VO 2 (i.e. loss of parallelism), while VT 2 was identified at the time of respiratory compensation or during the disproportionate increase in ventilation compared to VCO 2 . 17,23 For VT 1 or VT 2 , when the three evaluators identified identical values, that value was adopted. In the case of divergences between evaluators, the median result was chosen.

Statistical analysis
Descriptive analyses (mean and standard deviation) were performed. The normality of the data was verified by the Shapiro-Wilk test. Betweengroup comparisons were performed using Student' s t-test for independent samples (parametric data), or the Mann-Whitney U test (non-parametric data). All statistical tests were performed using SPSS software (v. 23.0; IBM Corporation, Armonk, New York, NY, USA), with α=0.05.

RESULTS
The characterization of the players is shown in Table 1. Regarding positions, soccer players included a goalkeeper, a full-back, four defenders, four defensive midfielders, three midfielders, and two forwards. Futsal players included two goalkeepers, four defenders, nine wingers, and two pivots. The groups were similar in terms of age and body mass; however, soccer players were taller.
No differences were found in VO 2 max and %VO 2 maxVT 2 between groups but soccer players had higher %VO 2 maxVT 1 , VT 1 and VT 2 . In addition, futsal players reached both VTs at lower speeds (Table 2).

DISCUSSION
This study aimed to compare aerobic performance indicators between soccer and futsal players. No differences were found in VO 2 max and %VO-2 maxVT 2 between groups. Percent VO 2 maxVT 1 was lower in futsal players, and their VT occurred sooner and at lower speeds than in soccer players. VO 2 max represents the maximal capacity of oxygen consumption and reflects level of fitness. We found no differences in VO 2 max between soccer and futsal players. These results agree with previous studies that controlled for stage of training. [8][9][10] Soccer and futsal players may have similar VO 2 max levels due to the intermittent high-intensity nature of their sports. 4 Contradictory values of VO 2 max were identified between soccer and futsal players in studies that did not control for stage of training. Karimi, Hojjati and Shamsi 7 found higher VO 2 max values in soccer players (57.42 ml•kg-1 •min-1 ) than futsal players (52.77 ml•kg-1 •min-1 ). According to the authors, this suggests an aerobic predominance in soccer, where the aerobic system is the main source of energy (70 to 90%) during a match/ training. 5,7,10,25 VO-2 max is linked to the distance covered during a match; thus, soccer players may have better endurance, withstanding longer periods of exercise until exhaustion. 8 On the other hand, Nunes et al. 5 found a higher VO 2 max in futsal players (62.5 ml•kg-1 •min-1 ) than in soccer players (52.1 ml•kg-1 •min-1 ). These authors attributed their results to the different training methods, levels of competitiveness and number of competitions between players. Therefore, the level of competitiveness of the teams may have influenced the results, as the futsal team in their study competed nationally while the soccer team competed at the state level. Since VO 2 max may vary during the season (3-7% lower at the beginning of the season than the end), 13 it is important to consider evaluation period, periodization of training, and level of competitiveness of players when different sports are compared.
VT 1 refers to the beginning of lactate accumulation during physical effort. 18 In our study, futsal players reached VT 1 at lower percentages of VO 2 max, and it occurred earlier and at lower speeds than in soccer players, suggesting earlier lactate production in futsal players. This may result from greater participation of anaerobic glycolytic metabolism in futsal players, while aerobic metabolism is still their main source of energy. 16 Despite this, VT 1 , which represents intensity of effort relative to VO 2 max, was lower in futsal than in soccer players and futsal players had a longer interval between VT 1 and VT 2 . According to Wilke et al., 17 intensity is divided into three zones: below VT 1 (low intensity), between VT 1 and VT 2 (moderate intensity), and above VT 2 (high intensity). It is reported that futsal players expend 73% of a training session below VT 1 , 20% between the VT 1 and VT 2 and 7% above VT 2 . 17 , while soccer players cover approximately 11 km in a match, with 3% and 5% of a training session spent sprinting and running at high-intensity effort, respectively. 26 Therefore, it is expected that futsal players have higher speeds during VT, since speedVT is highly correlated to the ability to perform repeated high-intensity sprints over time. 24 Contrary to our results, Ribeiro et al. 9 observed a higher speedVT 1 in futsal players (13.3 km/h) than soccer players (11.0 km/h); however, this study did not control for preseason period (initial and final). Ribeiro et al. 9 also adopted a more intense ramp protocol with an increase in speed of 1 km/h every minute, where testing lasted between 8-12 minutes, while we adopted a longer protocol (i.e. Bruce protocol) with increases in speed and inclination of 1.6 km/h and 2º at each 3-min stage, lasting up to 21 minutes. VT 2 represents the respiratory compensation point. 18 We found no differences in %VO 2 maxVT 2 between soccer and futsal players. This is in agreement with the results of Baroni et al., 8 who observed %VO 2 maxVT 2 at similar intensities (soccer = 87.89%; futsal = 88.29%). Nunes et al. 5 found higher %VO 2 maxVT 2 in futsal players (futsal = 93.9%; soccer = 76%), who reached VT 2 at higher intensities than soccer players. Our results may have been different from Nunes et al. 5 because our evaluations were performed at the beginning of the preseason, while Nunes et al. 5 did not mention the phase of the preseason in which players were evaluated. In our study, VT 2 was reached earlier (less time) in futsal than soccer players. Leal Junior et al., 10 also found that futsal players reached VT 2 earlier (11.4 min) than soccer players (14.0 min), suggesting that soccer players have a greater aerobic capacity. Like Baroni et al., 8 we found that speedVT 2 was greater in soccer players than futsal players. Soccer players reached both VTs at higher speeds (equivalent to time/test stage), where VO 2 increases as running speed increases, 27 suggesting that soccer players can withstand progressive effort for longer periods until exhaustion. 8 Our study had some limitations. Laboratory effort protocols, such as the one used in this study, are not very functional for soccer and futsal, while field tests have good applicability. 28,29 However, the procedures used in this study can be performed with athletes to assess basic physiological parameters (e.g. VO 2 max and VT), which assist in building highly specific training programs. 22,29 Participants in our study were not stratified by position, which could have minimized intragroup variation as there are different mechanical and physiological demands for each position. 8,18,30 However, the number of players evaluated did not allow for such stratification. To control these limitations, pre-training and post-training evaluations could be performed, and training routines and game calendars could be monitored. 18 This would allow us to identify adaptations to physiological parameters caused by training. 31 As well, the inclusion of other physiological markers such as blood lactate, 4,15,32 heart rate, 2,5 and subjective perception of effort, 31,33 could provide additional information about the demands of soccer and futsal and the physiological profiles of players.

CONCLUSION
In the preseason phase of the competitive calendar of soccer and futsal, male players have similar VO 2 max's and reach their VT at different times and speeds. Different levels of physical effort and physiological adaptations exist for each sport, indicating that training methods should be designed with each sport's specificity in mind.
All authors declare no potential conflict of interest related to this article Values expressed as mean and standard deviation (±); VO 2 max = maximal oxygen uptake; %VO 2 maxVT 1 = percentage of VO 2 max at first ventilatory threshold; VT 1 = first ventilatory threshold; speedVT 1 = speed during first VT; %VO 2 maxVT 2 = percentage of VO 2 max at second ventilatory threshold; VT 2 = second ventilatory threshold; speedVT 2 = speed during second VT. * = statistically significant differences between groups (p≤0.05).

AUTHORS' CONTRIBUTIONS:
Each author made significant individual contributions to this manuscript. MHG: substantial contribution to the conception and design of the work, analysis and interpretation of the data, writing the manuscript and preparing the final version of the manuscript; JMG: interpretation of the data, writing the manuscript, critical review of the intellectual content and final approval of the version of the manuscript; ANC: analysis and interpretation of the data, writing the manuscript and critical review of the intellectual content; PN: analysis and interpretation of the data, writing the manuscript and preparing the final version of the manuscript; GGR: substantial contribution to the concept and design of the work, analysis of the data; HHP): substantial contribution to the concept and design of the work, critical review of its intellectual content and final approval of the version of the manuscript. MBR: substantial contribution to the concept and design of the work, interpretation of the data, critical review of its intellectual content and final approval of the version of the manuscript.