The impact of the COVID-19 pandemic in sport has been the subject of numerous studies over the past two years. However, knowledge about the direct impact of COVID-19 infection on the performance of athletes is limited, and the importance of studies on this topic is crucial during the current pandemic era. This study aimed to evaluate the changes in the match running performance (MRP) of professional soccer players that occurred as a result of COVID-19 infection after fulfilling all of the prerequisites for a safe return to play (RTP). The participants were 47 professional soccer players from a team which competed in first Croatian division (21.6 years old on average) during the 2020/21 season. The total sample was divided into two subgroups based on the results of a PCR test for COVID-19, where 31 players tested positive (infected) and 16 tested negative. We observed the PCR test results (positive vs. negative PCR), the number of days needed to return to the team, number of days needed to RTP after quarantine and isolation, and MRP (10 variables measured by a global positioning system). The number of days where the infected players were not included in the team ranged from 7 to 51 (Median: 12). Significant pre- to post-COVID differences in MRP for infected players were only found for high-intensity accelerations and high-intensity decelerations (t-test = 2.11 and 2.13, respectively; p < 0.05, moderate effect size differences), with poorer performance in the post-COVID period. Since a decrease of the MRP as a result of COVID-19 infection was only noted in two variables, we can highlight appropriateness of the applied RTP. However, further adaptations and improvements of the RTP are needed with regard to high-intensity activities.

There are limited data describing clinical patterns and match running performance (MRP) among players with COVID-19 infection before and after infection, particularly related to different predominant SARS-CoV-2 variants, as well as in comparison to uninfected players. This observational study was conducted during two consecutive soccer seasons in one professional club in Split, Croatia. There were four clusters of mild, self-limited, or asymptomatic infection characterised by low adherence to preventive measures. Infected players had significantly more symptoms (t-test = 3.24; p = 0.002), a longer period of physical inactivity (χ² = 10.000; p = 0.006) and a longer period of self-assessment for achieving full fitness (χ² = 6.744; p = 0.034) in the 2020–2021 season (Wuhan wild strain and Alpha variant) than in the 2021–2022 season (Omicron variant). It was also found that, despite the milder clinical presentation of the infection in the 2021–2022 season, the players had significantly more abnormal laboratory findings (χ² = 9.069240; p = 0.002), although without clinical significance at the time of the study. As for the MRP, player performance in the 2021–2022 season was not negatively affected by the Omicron variant, while there was an improvement in MRP in scores for a sample of all players. The RTP protocol was correctly applied because it helped the athletes to recover their pre-infection physical capacities relatively quickly. This study advances the understanding that an optimally and individually planned RTP protocol is crucial for the MRP of infected players. Future research needs to replicate the findings of abnormal laboratory results and extend the study focusing on their potential long-term clinical significance.

To develop specific preventive strategies, it is necessary to investigate in detail the occurrence of injuries in young football players. This study aimed to provide details about the type, location, severity, and contact nature of muscle injuries in elite U15 Croatian football players. A total number of 130 muscle injuries occurred during the six competitive seasons, of which 88 were DOMS injuries and 42 were rupture injuries. Specifically, 87% of all muscle injuries belonged to the four major groups, with only 15 injuries to the other muscle groups: hamstrings (43), quadriceps (41), adductors (25), calves (6). The muscle injury incidence was stable during the observed period as the injury incidence rate ratio (IRR) was 1.01 (95%CI: 0.99–1.03), with 3.13 (95%CI: 3.09–3.17) muscle injuries per 1000 h of exposure in the first season and 3.06 (95%CI: 3.02–3.1) in the sixth season. A significantly higher risk for muscle injuries was discovered in the competition as the incidence for the whole observed period was 7.38 (95%CI: 7.29–7.47) compared to 2.25 (95%CI: 2.24–2.26) in the training period. Despite the relatively stable number of sustained muscle injuries, the relative proportion of muscular injuries increased over the years due to a severe decrease in the total number of injuries. Regarding the proportion of players who had sustained a muscle injury, our results suggest that approximately two out of five players can expect a muscular injury over the one-season period. Relatively high injury expectancy rates, as well as reinjury rates, require specific preventive interventions that will reduce the number and severity of new and recurred injuries. Future studies should include a wide set of predictor variables in order to establish the most important injury risk factors.

Although the effect of coach turnover is often discussed within the football community, there is a very limited body of knowledge on this topic. This study aimed to explore which coaching turnovers are associated with changes in injury incidence in an elite professional football club. A longitudinal study observed injury occurrence across the eight-season period, with the team experiencing 16 coaching changes, averaging 2 per season. All injuries were continuously monitored regularly recorded and saved in the club’s database. They were analyzed over three-time frames: for each season, 2 weeks after the coach was sacked, and also for 4 weeks after the coaching change. A paired sample t-test was used separately for the overall injuries and specifically for muscle injuries in the observed time frames. Overall injuries had an increase of 27.7% and 35.4% in the two and four weeks after coaching turnovers, respectively, while for muscle injuries, these rates were lower and amounted to 5.5% and 8.1%. There were no statistically significant changes, but a medium effect size was reported when comparing overall injuries in 4 weeks and the season in general. Muscle injuries appear to be less negatively affected by coaching changes. Club coaching and medical staff should be especially careful in controlling the training load and recovery techniques in the transition periods while also maintaining the club’s preventive methodology.

Injuries in elite youth football may disrupt training continuity and long-term development, particularly during the post-peak height velocity (post-PHV) period when training and match demands increase. Therefore, the aim of this study was to determine injury incidence and describe injury patterns in elite U17 football players across six consecutive competitive seasons, including injury type, anatomical location, mechanism, recurrence, and severity. A prospective longitudinal injury-surveillance design was implemented in one elite football academy from 2016/2017 to 2021/2022. Injuries were recorded in the club’s medical database using the international consensus time-loss definition. Injury incidence per 1000 h was calculated for overall exposure, training, and matches, and injuries were analyzed by diagnosis, mechanism, recurrence, and severity. Across the study period, 331 injuries were recorded. Overall injury incidence was 6.95/1000 h, with markedly higher incidence in matches (20.61/1000 h) than training (5.82/1000 h). Seasonal incidence ranged from 4.49/1000 h in 2019/2020 to 9.31/1000 h in 2021/2022. The proportion of injured players ranged from 48% to 76% per season. The most frequent injuries were contusions and muscle cramps/DOMS, followed by ligament injuries, tendinosis, and muscle ruptures. Knee, thigh, ankle, and hip/groin were the most affected regions. Most diagnoses showed a predominantly non-contact pattern. These findings support targeted prevention and load-management strategies in elite youth football.