Futsal is a competitive ball sport consisting of short duration sprints interspersed with short recovery periods (Naser et al., 2017). The repeated high-intensity nature of futsal requires players to develop high-levels of both long duration exercise and short duration exercise capacity (Castagna et al., 2009). Indeed, previous research reported that professional players can develop maximum oxygen consumption (V[O.sub.2max]) values in excess of 60 ml*[kg.sup.-1]*[min.sup.-1] to cope with the games physical requirements (Alvarez et al., 2009; Castagna et al., 2009). Futsal players typically cover 3-5 km during a game and more than 50% of the time is performed at a high intensity (Castagna et al., 2009; Naser et al., 2017). A previous study has reported players achieve a mean blood lactate concentration of 5.3 mmol*[L.sup.-1] and spend ~80% of actual playing time at exercise intensities higher than 85% of their maximum heart rate (HRmax) (Barbero-Alvarez et al., 2008).
To date, there is little research investigating the actual training of futsal players (Barbieri et al., 2016; Berdejo-del-Fresno et al., 2015). Traditionally, training has focused on a combination of generic team-sport exercises, aimed at improving repeated sprint ability and long duration exercise capacity and simulated game play to enhance skill and techniques (Barbieri et al., 2016). A recent trend in team sports has seen an increase in the use of small-sided game (SSG) to not only improve the players technical and tactical aspects but also provide a time-efficient method for improving players physical condition (Amani-Shalamzari et al., 2019b; Halouani et al., 2014b). Compared to generic training the use of SSGs provides the added benefit of allowing for more training time spent developing game relevant skills and tactical abilities while simultaneously providing game specific fitness (Amani-Shalamzari et al., 2019b; Engel et al., 2018; Helgerud et al., 2001).
Given time constraints, coaches are constantly looking for exercises that may further enhance the effectiveness of the available training sessions. One that has received recent attention is the use of limb blood flow restriction (BFR) (Pope et al., 2013). Tourniquets or pneumatic cuffs are used to occlude or restrict venous return and restrict arterial blood flow during exercise with BFR (Pope et al., 2013). Using BFR during training reduces the amount of oxygen and nutrients supplied to active muscle thereby increasing hypoxic conditions and placing the muscle under greater metabolic stress (Tanimoto et al., 2005). Recently research suggests that occlusion, when used in conjunction with training, may provide greater gains in both aerobic and anaerobic performance (de Oliveira et al., 2016). Previous research has also suggested that BFR training may cause increases the levels of hormones related to muscle hypertrophy like growth hormone (GH) and insulin-like growth factor-1 (IGF-1) (Abe et al., 2005; Takano et al., 2005b). The majority of early research has utilized BFR in conjunction with low-intensity aerobic (
Adding BFR to exercise increases the metabolic load (internal exercise load), which leads to further metabolic adaptations such as lactate maintenance during exercise. Due to the specificity principle of training for train based on muscle involvement pattern in the futsal, we hypothesis that adding BFR to 3-a-side game which is predominantly dependent on the aerobic system leads to increase the exercise metabolic load and as well increased lactate tolerance, which players often encounter during the futsal games. Therefore, the aim of the current study was to investigate the utility of BFR used in combination with SSG training for enhancing the long and short duration exercise capacities of futsal players. We hypothesized that high metabolic pressure during the BFR may cause to improve performance in futsal players.
Experimental approach to the problem
The study was a control-trial in which subjects were randomly assigned to either an experimental (BFR n = 6) or control group (non-BFR n = 6) for ten sessions of game-specific futsal training.
Twelve male futsal players aged 23 [+ or -] 2 years, body height 1.74 [+ or -] 0.05 m, body weight 67.5 [+ or -] 6.8 kg, BMI 22.2 [+ or -] 2.0 kg/[m.sup.2], with at least five years' experience in futsal (played at National League Second Division) volunteered to participate in this study. All subjects were in healthiness without any orthopedic, neuromuscular or cardiovascular diseases and provided written informed consent before testing. They excluded from the study if they had more than one session absentee. The study was a controlled trial in which subjects were randomly assigned to either an experimental (BFR n = 6) or control group (non-BFR n = 6) for ten sessions of game-specific futsal training. In order to estimate the number of participants needed in the study, a sample size calculation was performed using G*Power Software version 126.96.36.199 (Dusseldorf, Germany) (Faul et al., 2007) for a repeated measures ANOVA (within factors), using an [alpha] rejection criterion of 0.05 and 0.95 (1-[beta]) power, and an average correlation of rho = 0.50 between the repeated measures for 4 within subject measurements to detect a medium effect (f = 0.5). The power calculation indicated that a minimum of 12 participants was required to be able to find such an effect. All experimental procedures were approved by the Ethics committee of Sport Sciences Research Institute of Iran with code IR.SSRI.REC.1396.187 and were conducted in accordance with the Declaration of Helsinki. The researcher explained the risks and benefits of the study to participants and obtained written informed consent prior to initial assessments.
The strength, muscle activation, and hormones (IGF-1 and myostatin) data have been published (Amani-Shalamzari et al., 2019a), but complementary data on aerobic and anaerobic performance, blood lactate concentration, and Hormones (Testosterone, GH, and cortisol) have not previously been analysed or reported.
Subjects completed a series of physiological and performance tests over three days, one week before and after a 3-week (10 sessions) training intervention. A schematic showing the testing timeline is shown in Figure 1. Physiological tests were performed in a temperature-controlled laboratory environment and consisted of a V[O.sub.2max] test followed by a time to fatigue (TTF) test on day two followed by a Wingate 30-second maximal test (WANT) on day three. On Day one, subjects initially completed an incremental speed test on a motorized treadmill (Pulsar hp Cosmos, Nussdorf-Traustein, Germany) set at a 1% inclination for determination of V[O.sub.2max]. The treadmill test commenced at 10 km*[h.sup.-1] and progressed with speed increments of 1 km*[h.sup.-1] every 3 min until subjects reached voluntary exhaustion. Throughout testing respiratory gases were measured using an alpha gas standard calibrated metabolic system (MetaLyzer3B, CORTEX, Leipzig, Germany). V[O.sub.2max] was calculated as the highest oxygen consumed over a 30 s period. V[O.sub.2max] was confirmed when 3 or more of the following criteria were met: (1) a plateau in V[O.sub.2] despite an increase in running speed; (2) a respiratory exchange ratio (RER) higher than 1.2; (3) peak heart rate at least equal to 90% of the age-predicted maximum; and/or (4) visible exhaustion (Bayati et al., 2011). Each subject's velocity at V[O.sub.2max] (vV[O.sub.2max]) was identified from the respiratory measures as the minimum velocity at which the recorded V[O.sub.2max] was initially obtained. Also a measure of running economy (RE) was identified using the mean absolute oxygen cost (L*[min.sup.-1]) measured during the final 2 min of the 11-km*[h.sup.-1] running stage. This running economy occurs below a respiratory exchange ratio of 1.0 that is between 7 and 12 km*[h.sup.-1] dependent on each individual's running ability (Paton et al., 2017).
On next day, the incremental test subjects completed a treadmill TTF at their previously determined vV[O.sub.2max]. Subjects commenced the TTF test at 60% of their vV[O.sub.2max], and then progressively increased to 100% vV[O.sub.2max] over a 30-45 s period. Total run duration was taken from the moment speed equaled the target vV[O.sub.2max] until subjects volitional exhaustion. For comparison, both pre and post-training vV[O.sub.2max] tests were performed at the same pre-training vV[O.sub.2max] velocity. On the following day, subjects performed a 30-s Wingate test on a stationary bicycle ergometer (Model 894E, Monark, Vansbro, Sweden) to obtain measures of peak power (PP), average power (AP) and minimum power (MP). Subjects commenced the WANT test with a 4-min warm-up performed at 60 revolutions per minute (RPM) against basket weight only (=60W). On completion of the warm-up subjects were immediately given a 5 s countdown to the automatically controlled beginning of the test. During the test subjects pedaled as fast as they could for 30 s while remaining seated. The resistance load for the Wingate test was set equivalent to 7.5% of each subjects' body weight. Players were verbally encouraged during all tests to perform to their maximum ability. As reported the...