Small-sided games (SSGs) are extensively used in football training with the aim of concurrently simulating a variety of technical and physical aspects of the sport (Hill-Haas et al., 2009). In this regard, the implementation of SSGs has been shown to be effective in developing aerobic and anaerobic endurance, agility and strength in players at different standards of play (Los Arcos et al., 2015; Owen et al., 2012).
Among the vast array of football-specific tasks (e.g., SSGs, modified games, conditioned games, etc.) currently available, small-sided ball possession games (SSBPGs) are extensively used to develop combinative playing skills. In these drills, the generic aim is to conserve ball possession with no goals or goalkeepers involved, while the four moments of the game (i.e., offensive organization, defensive organization and both offensive and defensive transitions) are present (Winter and Pfeiffer, 2016). Moreover, the spatial structure of the team and tactical tasks associated with the different playing positions, although simplified in comparison to an 11 vs. 11 game, can be maintained.
The idea that the physical demands of competition present large inter-player and intra-player variability is not new (Carling 2013; Di Salvo et al., 2007). One of the variables that can greatly influence a player's physical activity during a competitive match is the position they occupy on the pitch (Castellano et al., 2014; Di Salvo et al., 2007). Thus, it would appear desirable that training drills aiming to improve game-related physical performance effectively address these positional-specific demands observed during matches. In overall terms, SSGs typically present lower demands relating to high-speed running (HSR) and sprint actions, and greater acceleration-deceleration demands than competitive matches (Beenham et al., 2017; Casamichana et al., 2012; Dellal et al., 2012; Gimenez et al., 2018). The magnitude of these differences increases when the number of players and/or pitch dimensions are reduced (Casamichana and Castellano, 2010; Hill-Haas et al., 2009).
Recently, Lacome et al. (2017) compared competitive match demands with those imposed by different SSGs and modified games, considering the playing position of players in the competition. The main findings revealed that, when compared with the most demanding passages (MDP) of the competitive matches, there were substantial differences depending on positional role, with central defenders and midfielders being the most over-stimulated and under-stimulated during the SSGs compared to competition respectively. Despite the study by Lacome et al. (2017), the possible differences that SSGs might impose on the different playing positions remain largely unexplored.
To date no comprehensive evaluation of the physical demands of SSBPGs in comparison with game demands and specific to each playing position has been conducted. Therefore, the aim of this study was to quantify the external training load that the different positions are exposed to during different SSBPGs when compared with the MDP of competitive matches.
Global Positioning System (GPS) data were collected during the 2015-2016 competitive season to establish the position-specific demands of the competitive matches and the different SSBPGs. Demands were expressed in values relative to practice time (m*[min.sup.-1] for example) and values relative to the most demanding passages of play (% of the MDP) in competitive football matches over a similar duration (3 or 5 minutes).
Data were collected from 25 football players (20.4 [+ or -] 2.1 yrs, 1.78 [+ or -] 0.66 m, 69.7 [+ or -] 6.1 kg) belonging to the reserve squad of a Spanish La Liga Club. At the time of writing, the first team squad has been ranked among the top six in the last 10 seasons and ranked as the top team in the last three seasons according to official UEFA rankings. Players were grouped according to their playing position as central defenders (CD, n = 4), full backs (FB, n = 6), midfielders (MF, n = 3), wide midfielders (WMF, n = 5) and forwards (FW, n = 7). Data arose as a condition of the players' employment whereby they were assessed daily and thus no authorization was required from an institutional ethics committee (Carling et al., 2016; Lacome et al., 2017). Nevertheless, this study conformed to the Declaration of Helsinki and players provided informed consent before participating.
Thirty-seven competitive matches in the 2015-2016 season were included in the analysis (13 wins, 15 losses, 9 draws, final league position 11 (th) ). The team systematically played in a 1-4-3-3 formation with a goalkeeper, four defenders (two FBs and two CDs), three midfielders (a MF and two WMFs) and three FWs. Goalkeepers and players with fewer than six records were not included in the analysis. Only data from players who completed the full match were analyzed. A total of 227 individual GPS files from match data on reserve team players belonging to a professional male football team were collected, with this distribution per position: CD = 42, FB = 60, MF= 40, WMF = 34, and FW = 51 GPS files.
Small-sided ball possession games
The SSBPGs were structured according to the position of the player in the game system (wide players occupied the positions closest to the narrow side line and MF and WMF occupied the inner positions). The main offensive objective of the positional games was to maintain possession of the ball in superiority with three jokers (Jk). Quick pressure after losing ball possession was the main defensive tactical concept. The characteristics of each of the SSBPGs analyzed in the current study were as follows (Figure 1):
4v4+3: four against four players plus three Jks. Duration: 02:48[+ or -]00:37 min. Dimensions: 13 x 17 m, surface area per player: 21.0 [m.sup.2]; one of the Jks is located inside and the other two Jks on the sides of the playing area, which creates an overload of 7 vs. 4 in the possession phase.
5v5+3: five against five plus three Jks. Duration: 03:48[+ or -]00:43 min. Dimensions: 25 x 20 m, surface area per player: 38.5 [m.sup.2]; one of the Jks is located inside and the other two Jks on the sides of the playing area, which creates an overload of 8 vs. 5 in the possession phase.
7v7+3: seven against seven plus three Jks. Duration: 05:18[+ or -]00:40 min. Dimensions: 29 x 36 m, surface area per player: 61.4 [m.sup.2]; one of the Jks (always a MF) is located inside and the other two Jks (always a CD and FW) on the sides of the playing area, which creates an overload of 10 vs. 7 in the possession phase.
8v8+3: it is eight against eight plus three Jks. Duration: 05:23[+ or -]00:37 min. Dimensions: 40 x 35 m, surface area per player: 73.7 [m.sup.2]; one of the Jks is located inside and the other two Jks on the sides of the playing area, which creates an overload of 11 vs. 8 in the possession phase.
Variables and MDP of the games
The variables recorded were relativized to metres per minute (m*[min.sup.-1]): the distance covered (TD), distance covered at high speed running (HSR: >19.8 km*[h.sup.-1], m*[min.sup.-1]), distance covered in sprinting (SPR: >25.2 km*[h.sup.-1], m*[min.sup.-1]), the number of high intensity accelerations and decelerations (ACC/DEC: >3 m*[s.sup.-2], n*[min.sup.-1]), the high metabolic load distance (HMLD; >25.5 W*[kg.sup.-1], m*[min.sup.-1]), and the average metabolic power (AMP: W*[kg.sup.-1]). The intensity thresholds used were the same as those employed in previous studies (Osgnach et al., 2010; Owen et al., 2017; Stevens et al., 2017; Tierney et al., 2016). ACC/DEC in the STATSports software was calculated from the differentiated GPS Doppler speed; for an ACC/DEC to register it had to have a minimum duration of 0.5 seconds and a minimum magnitude of 0.5 m*[s.sup.-2] (Varley et al., 2017).