This study aimed to analyze the A-S profile of elite football players according to different playing positions, training days and matches. To the authors’ knowledge, this is the first study in the literature to conduct a longitudinal observation (six weeks in a row) of this profile. The longitudinal observation offered reliability on the results showed, in which differences between microcycle session days and within playing position were found for all included variables of the A-S profile.
Previous investigations have already described the A-S profile in two non-consecutive microcycles (15) showing mean values without categorizing by playing position or microcycle day. Reference values offered by Morin, et al. 15 are 9.47 ± 0.52 m/s and 7.2 ± 0.4 m/s2 for S0 and A0 respectively in a whole microcycle. However, our study showed that S0 and A0 depends on playing position and microcycle day, showing a range from 5.66 ± 1.35 m/s (MF on MD-2) to 9.5 ± 0.34 m/s (WMF on MD) for S0 and 5.73 ± 1.13 m/s2 (FB on MD-2) to 8.68 ± 0.63 m/s2 (CD on MD) for A0. Also, S0 range values in MD of this study are similar to V0 values analyzed in linear tests of the force-velocity profile by previous studies: 9.25 ± 0.46 m/s (13), 9.25 ± 0.61 m/s (24) and 9.2 ± 0.4 m/s (25), when analyzed single sprinting F-V profile of elite football players. Furthermore, A0 values found, result similar to F0 values showed by Jimenez-Reyes, et al. 13, Jiménez-Reyes, et al. 24 and Haugen, et al. 25, 7.14 ± 0.58, 7.35 ± 0.69 and 8.4 ± 0.5 m/s2 respectively. A-S profile gives also more specific data because it is obtained within a huge number of on-field football actions. However, more investigations are needed to surely stablish a correlation between A0 and F0 and between S0 and V0 in elite football. If both profiles were similar, A-S profile could and used for fatigue and injury management (16,26,27).
Concerning ACCmax and Smax, previous studies have already shown significant differences between playing positions (4,13,19). Highest Smax was reached by WMF on MD (8.82 ± 0.41 m/s) and the lowest by MF (7.96 ± 0.57). Similar results to our study were found in other research in a team of the same division, in which WMF got the greatest one (8.88 ± 0.44 m/s) and MF the lowest one (7.91 ± 0.47 m/s) for Smax on MD. Physical demands are specific for a determined playing position (20,28) and this justify the variations found in this article for the A-S profile´s variables.
Although more investigations are required, the continuous evaluation offered by the A-S profile allows to prescribe specific training, not only by day of the microcycle but also by playing position. Also, A-S profile also could allow to detect imbalance in acceleration and speed capabilities. Determining an optimal A0 and S0 for elite football players could be interesting to set specific and individualized training programmes (18,29-31) for each playing position and player in order to improve a concrete range of the A-S spectrum. For example, greatest values for Smax on MD were found on WMF, who reached the lowest ACCmax. In this case, specific training should be programmed for WMF in order to improve the ACCmax, with very heavy sled sessions (31,32). On the other hand, positions with the lowest speed in both theoretical and maximal values should choose light loads (<10% Body mass) with the aim of improving the right side of the A-S profile profile which corresponds to maximal velocity (33).
More significant differences were found for ACCmax and Smax than for A0 and S0. This could be explained because A0 and S0 are theoretical values, and its accuracy depends on the R2 coefficient. On MD-2, higher number of significant differences were found. Closer proximity to MD is highlighted as a tapering period in which training load significantly decreases (34,35). The reason might be that closer proximity to MD, lower load for the team selected in this research.
Although not many significant differences where found for AS slope far from MD-2, it is considered as performance indicator of acceleration and sprint. More significant differences might be found inter-athletes.
This research presents some limitations that need to be considered. Football is an intermittent sport in which the physical demands oscillate depending on the style of playing and training, the team formation and the individual characteristics of players from the same position. This study included one team from a specific country, with its particular playing style and level within the league. Future research should include more teams from different competitions in order to provide results that could be extrapolated to different elite teams.
This study provides a meaningful and novel description of the differences found in the A-S profile of elite football players. Results showed significant differences for the variables of A-S profile analyzed within position and day of the microcycle. Players reached the higher values on MD, which means that is the most demanding day and it is not reproduced on any training sessions. Furthermore, it must be highlighted that CD is the position with higher values in acceleration variables. However, WMF showed the highest values for velocity variables.
The article offers values of elite football players for practitioners who need some reference about the A-S profile variables to understand the individual nature of this profile. This would help sport scientists and fitness coaches to understand the variability of this profile and design orientated sessions according to the specific positional demands. Therefore, the results might allow to relate F-V and A-S profile in the future considering the potential advantages of applying the A-S profile in elite contexts (e.g., “testing without testing”). Analyzing A-S profile workload could be prescribed precisely and individualized to each player, attending to the profile range that needs to be improved. For example, it allows to identify both acceleration or speed deficits. Moreover, the A-S profile gives information about the physical orientation of the training session and whether MD´s demands are covered along the training week.