The aim of this study was to analyze the changes in match performance parameters (e.g., high speed running, maximum speed, playing time) in professional soccer players after sustaining an injury, adjusting for injury severity. The main novelty of this study is the pre-post injury comparison of external loads combined with playing time in professional soccer players. This study showed a significant reduction in playing time after suffering moderate and major injuries, because players were less used as starters following major injuries after the return to play. Additionally, significant reductions were observed in distances covered in jogging and running speed after minor injuries, while players who suffer major injuries covered significantly greater distances at intense running and high-speed running (mainly in + 4 match). Finally, a decrement in the maximum speed was found after moderate and major injuries. In this sense, the initial hypothesis has been verified.
To fully understand the real impact of injuries, it is necessary to evaluate performance variables and playing time in post-injury matches. This investigation analyzed the participation of injured players after the return to play, showing that players returned to be used as starters with the progressive succession of the matches considering every injury severity. Participation as starters after a major injury in early matches after the return to play (i.e., + 1 and + 2 matches) was reduced. This could be due to the necessity of a progressive return to competition when the amount of absence was longer, which is due to the severity of the injury [10, 33], which influenced the overall playing time. Although a reduction in playing time was not found after minor injuries, the results of the present study showed that this is the case after suffering moderate or severe injuries (mainly in + 1 matches). This finding represents a key problem for the team performance because the athletes’ availability following a moderate or major injury was prolonged and went beyond the return to play [10, 34]. Team performance could have been affected because specific players did not perform similar match performance parameters as before injury (such as minutes of play) until they have played some competitive matches that were needed to recover the previous physical level [7, 35].
Common parameters in the analysis of external demands in soccer matches are the total distance (TD) and RD [36], so it seems pertinent to analyze the impact of injuries on these variables after the return to play. In this sense, no significant differences in RD between the pre-and post-injury values were reported for any injury severity. However, while a trend toward a reduction in RD was observed after minor injuries, an increasing trend was found after moderate and major injuries, which could have been possibly influenced by the reduction in playing time experienced by players who suffered these injuries. On the other hand, although no significant differences were observed in walking distance in any severity, players who suffered minor injuries revealed a significant reduction in the distance covered at jogging and running during first matches, showing significant differences with moderate and major injuries. We suppose that players suffering minor injuries could have participated in official matches without being fully recovered in terms of health readiness [21], which could have altered their match performance (this is a possible explanation). According to a previous study [23], we have found a significant post-injury increment in the running speed distance in players suffering moderate and major injuries, which were significantly higher compared with minor injuries.
Since the positive influence of high-intensity actions on soccer players’ performance during matches [27, 37], the monitoring and control of these actions after an injury seem crucial to ensure an adequate return to play [33]. Players who suffered major injuries reported significantly greater distances in the intense running and high-speed running categories, mainly in the last match analyzed (i.e., + 4), which is in agreement with previous research [23]. Some motivations of this result could be associated with the fact that these players have dedicated more time to train high-speed running [33], along with greater control of the load and fatigue during the reconditioning program [23], or, another possible explanation is that players suffering minor injuries were reincluded in the team as starters before a full recovery, therefore their match performance was affected. These findings show that after sustaining moderate and major injuries, soccer players returned to play executing similar or even better external performance compared to their previous level, however authors cannot explain the motivations of this with certainty. The external load metrics reported in this study were unified based on players played time, therefore the reduced playing time reported after some injuries can explain the similar external load performance reported compared to pre-injury. Although players maintained their pre-injury performance, they did it for less time, especially in the + 1 match. For this reason, it seems appropriate to suggest that during rehab programs external demands should not only be controlled in terms of absolute values (volume = 45 or 90 min), but also in relation to time (intensity = per min). Practitioners should develop return to play protocols that have a similar relative intensity of the matches and, with the right progression, increase the overall volume (training time) to fully prepare their players for the match.
Regarding the distance covered at sprinting speed, only certain increases were observed after minor injuries, while these were not reported after moderate and major injuries. This seems to be related to the maximum speed variable, which is significantly impaired after returning to play after suffering moderate and major injuries along the four matches analyzed. These results do not support those previously reported by Jiménez-Rubio et al. [23], who observed significant improvements in the maximum speed after the return to play compared with previous values. These results, which are in contrast with ours, could be due to methodological differences between the studies since in the aforementioned investigation all the players followed the same reconditioning program after they sustained the same injury (i.e., grade IIb hamstring strain injury), while a smaller sample was used (22 vs. 207 injuries). This reduction in the maximum speed observed in our study may suggest that soccer players, who have sustained moderate and major injuries, were not as physically fit as before the injuries despite returning to play protocols. Thus, they needed several official matches to regain their previous level, which may have a negative effect on the team performance given the importance of maximum speed during the match [37]. Therefore, strategies to improve the maximum speed level should be implemented during reconditioning processes.
This study is not without its limitations, firstly, only time parameters and external demands were considered, despite the importance of physiological variables during return to sport protocols [38, 39]. Secondly, this study focused on external load parameter recorded during matches, while physical tests may have added some important information. Furthermore, only players from the Spanish Premier League were involved in this study, and this could limit the application of these findings to other leagues. This is due to the fact that competitive demands vary between the main professional soccer leagues, however, future studies could replicate the protocol reported in this study and investigate other championships. Finally, there is no information on the rehabilitation programs followed by each team, which could have been different among them, and therefore, they may have influenced the post-injury performance reported in this study.