No major changes in injury incidence in European club football during the 2022/23 FIFA World Cup season: a subanalysis of the UEFA Elite Club Injury Study

Abstract

Objectives

To compare injury incidences between the 2022/23 season and the preceding five seasons, and between World Cup players and non-World Cup players during the 2022/23 season.

Methods

During the 2022/23 season, 29 teams participated in the Union of European Football Associations Elite Club Injury Study and reported football exposures and injuries prospectively. Injury incidence was compared with that of the five preceding seasons for the full season and for periods before and after the Fédération Internationale de Football Association World Cup 2022. In addition, World Cup players were compared with non-World Cup players. Incidences were compared using rate ratio (RR) with 95% CI.

Results

Injury incidences during the 2022/23 season were similar to previous seasons except for training incidence which, due to a significantly lower incidence in the 2017/18 season compared with all other seasons, was higher during the full season (RR 1.10, 95% CI 1.00 to 1.21) and in the period before the World Cup (RR 1.17, 95% CI 1.02 to 1.35). World Cup players had similar injury incidences before and after the tournament (training incidence; RR 0.95, 95% CI 0.65 to 1.38, match incidence; RR 1.15, 95% CI 0.87 to 1.52) but a significantly lower match incidence than non-World Cup players before the tournament (RR 0.84, 95% CI 0.71 to 1.00).

Conclusions

No major changes in injury incidences were observed during the 2022/23 season compared with previous seasons. World Cup players experienced similar injury incidences before and after the tournament, and had a lower match injury incidence before the tournament compared with non-World Cup players.

WHAT IS ALREADY KNOWN ON THIS TOPIC

• The Fédération Internationale de Football Association (FIFA) World Cup Qatar 2022 was scheduled to coincide with the middle of the European club season.

• This led to an increased match load during specific periods of the season and relatively short time to prepare for and recover after the World Cup.

WHAT THIS STUDY ADDS

• The injury incidence during the 2022/23 season was, in general, similar to previous seasons.

• The incidence of training injuries was slightly higher than in previous seasons. This difference appears to be due to a significantly lower training injury incidence during the 2017/18 season rather than a sudden increase during the 2022/23 season.

• The match injury incidence during the 2022/23 season was similar to that of previous seasons, considering the whole season as well as the periods before and after the World Cup.

• Players who participated in the World Cup did not experience an increase in injury incidence after the tournament.

HOW THIS STUDY MIGHT AFFECT RESEARCH, PRACTICE OR POLICY

• Scheduling the World Cup during the winter months of 2022 did not seem to cause major changes in injury incidences in European professional club football during the 2022/23 season. This study could potentially serve as a benchmark for future research and stakeholder planning before, during and after tournaments in similar conditions, such as the FIFA World Cup in Saudi Arabia 2034.

Introduction

Historically, the Fédération Internationale de Football Association (FIFA) World Cups have been played during the summer months, coinciding with the off-season for most professional domestic leagues as well as European international club tournaments.

Qatar hosted the FIFA World Cup 2022, and due to the potential for extreme heat during the summer months,¹ it was decided to schedule the tournament between 20 November and 18 December in a more favourable climate period. This scheduling forced European competitions to rearrange their match schedules to accommodate the World Cup,² causing increased match congestion both before and after the tournament, which could potentially influence the injury landscape.³ Indeed, a recent study on 17 teams in the French Ligue 1 revealed a significantly increased incidence of injuries during the 2022/23 season compared with the previous season.⁴

International tournaments also carry a high risk of injury.⁵,¹¹ Since the period between the World Cup and the resumption of club competitions was shorter following the 2022 tournament than would typically be the case after an off-season tournament,² the risk of continued injury absences in club teams due to injuries sustained during the World Cup may have also been increased.

The objective of this study was to compare injury incidence rates between the 2022/23 season and the preceding five seasons of historical data, as well as between World Cup players and non-World Cup players during the 2022/23 season. We hypothesised that injury incidences during the 2022/23 season would be higher than in previous seasons and that World Cup players would be particularly susceptible to injuries during the continued club season after the World Cup.

Material and methods

This is a substudy of the Union of European Football Associations (UEFA) Elite Club Injury Study (ECIS), a prospective cohort study commissioned by UEFA that has monitored injuries in European men’s professional club football consistently since 2001. The general methodology of ECIS adheres closely to consensus on how to conduct epidemiological studies in the field¹²,¹⁴ and has been described in detail previously.¹⁵

Participating clubs

At the start of a season in European football, clubs that have qualified for the group stage of the UEFA Champions League (UCL) are invited to take part in ECIS. To increase data consistency, teams that participated in ECIS in the previous season are invited to continue their participation even if they do not qualify for the UCL. For the 2022/23 season, 25 (78%) of the 32 teams that qualified for UCL agreed to participate in ECIS. Four additional teams agreed to continue their participation, bringing the total number of participating teams to 29. Study participation in the five preceding seasons, which were included as historical data comparison, was similar with 34 teams in 2017/18, 30 teams in 2018/19, 28 teams in 2019/20, 27 teams in 2020/21 and 25 teams in 2021/22. All first-team players were included in the study after providing their written and informed consent.

Data collection

At the time of study inclusion, teams assigned a member of their medical staff to serve as the contact person for the study. These contacts were provided with a study manual with detailed descriptions of the study methodology and operational definitions. Contact persons were also in continuous contact with members of the study group during participation to answer questions about the study procedure.

All training sessions and matches were registered, along with the individual duration of exposure in minutes. The attendance record also contained information about player absences due to injury, illness, national team duty or other reasons.

An injury was defined according to time-loss as “any physical damage that occurs during a training session or match which results in the player being unable to participate fully in training or a match the same day or subsequent days”.^{12 14 15}

The injury forms included information about the injury occasion and the diagnosis of the injury.

All data were sent to the study group monthly, and prompt feedback was returned to the clubs to enable them to complete any missing information or clarify any uncertainties.

Statistical analysis

Injury incidence is reported as the number of injuries per 1000 hours of exposure [(Σ injuries/Σ exposure hours) × 1000] with corresponding 95% CI. Muscle injuries were analysed separately, as this is the most common injury type in professional football,¹⁶ and it is suggested to be most affected by match congestion.^{17 18}

Injury incidences were computed for the full seasons, for the period before the World Cup (start of season to 19 November), and for the period after the World Cup (19 December to end of season). Injury incidences in these periods were then compared with data from the five preceding seasons (2017/18 to 2021/22), similar to what has been done previously,¹⁹ and presented as a rate ratio (RR) with 95% CI. Additionally, within-season injury incidences for World Cup players were compared with those of non-World Cup players during the 2022/23 season. RRs were tested for statistical significance using Z-statistics. These analyses were two-sided, and the significance level was set at p<0.05.

Injury incidences and exposure variables during the 2022/23 season were also calculated and presented every month, along with the median and IQR of these variables in the five previous seasons (2017/18 to 2021/22) for visual comparison.

If players returned from the World Cup with injuries sustained during the tournament that caused a continued absence, the number of absence days resulting from these injuries after the end of the World Cup was aggregated. These absences were presented as a proportion of all absence days caused by injuries during the season and in the period after the tournament.

Results

A total of 913 unique players from 29 teams participated in the 2022/23 season; 219 players (24%) were included in World Cup squads. In total, 176 790 exposure hours and 1123 injuries were reported during club trainings and matches over the 2022/23 season. Figure 1 illustrates monthly training and match exposure during this season compared with the five preceding seasons in terms of hours per month and training/match exposure ratio. Exposure variables during the 2022/23 season were generally similar to those in previous seasons, but a significantly increased number of match hours was registered in October 2022. In addition, during the World Cup months (November and December 2022), significantly fewer match hours were registered than in previous seasons, while training exposure was lower in November only.

Figure 1. Monthly exposure in terms of training hours, match hours and training/match hours per player and month during the 2022/23 season compared with historical data from five seasons (2017/18 to 2021/22). The shaded areas represent the IQRs for the period 2017/18 to 2021/22.

The injury incidences during the 2022/23 season were 3.5 (95% CI 3.2 to 3.9) injuries per 1000 training hours and 21.1 (95% CI 19.5 to 22.9) injuries per 1000 match hours. While no difference was found for match injury incidence during the 2022/23 season compared with combined data from the five previous seasons, training injury incidence was significantly higher (table 1). However, as figure 2 illustrates, there was no major change in training injury incidence during the 2022/23 season compared with the most recent seasons (2018/19 to 2021/22). Instead, a significantly lower training injury incidence was observed during the 2017/18 season. The figure also shows a relatively stable match injury incidence with no sudden increase during the 2022/23 season. Muscle injury incidence was similar in 2022/23 compared with previous seasons in both training and match play (table 1).

Table 1. Injury incidences and rate ratios comparing the 2022/23 World Cup season with the five preceding seasons.

	Preceding seasons	WC season	Rate ratio (95% CI)	P value
Full season
Training injury incidence (95% CI)	3.2 (3.1 to 3.3)	3.5 (3.2 to 3.9)	1.10 (1.00 to 1.21)	0.049
Match injury incidence (95% CI)	21.5 (20.7 to 22.3)	21.1 (19.5 to 22.9)	0.98 (0.90 to 1.07)	0.687
Training muscle injury incidence (95% CI)	1.6 (1.5 to 1.7)	1.7 (1.5 to 2.0)	1.08 (0.94 to 1.23)	0.290
Match muscle injury incidence (95% CI)	10.6 (10.1 to 11.2)	10.5 (9.3 to 11.7)	0.98 (0.87 to 1.12)	0.807
Season start to 19 November*
Training injury incidence (95% CI)	3.0 (2.8 to 3.2)	3.5 (3.1 to 4.0)	1.17 (1.02 to 1.35)	0.026
Match injury incidence (95% CI)	20.9 (19.7 to 22.2)	20.6 (18.2 to 23.2)	0.98 (0.86 to 1.12)	0.804
Training muscle injury incidence (95% CI)	1.5 (1.4 to 1.7)	1.8 (1.5 to 2.2)	1.19 (0.98 to 1.45)	0.083
Match muscle injury incidence (95% CI)	9.9 (9.1 to 10.7)	10.0 (8.5 to 11.9)	1.02 (0.84 to 1.23)	0.850
19 December to end of season†
Training injury incidence (95% CI)	3.4 (3.2 to 3.6)	3.4 (3.0 to 3.8)	1.00 (0.87 to 1.15)	0.975
Match injury incidence (95% CI)	21.5 (20.4 to 22.7)	22.2 (19.9 to 24.7)	1.03 (0.91 to 1.16)	0.642
Training muscle injury incidence (95% CI)	1.7 (1.6 to 1.8)	1.6 (1.3 to 1.9)	0.92 (0.75 to 1.12)	0.386
Match muscle injury incidence (95% CI)	10.9 (10.1 to 11.7)	11.0 (9.5 to 12.9)	1.01 (0.85 to 1.20)	0.883

Injury incidence is presented as the number of injuries per 1000 hours of exposure. Text in bold indicates a significant difference.

^*Period from the start of the season to the start of the World Cup.

^†Continuation of the club season after the World Cup.

WC, World Cup.

Figure 2. Training injury incidence and match injury incidence, presented as the number of injuries per 1000 hours of exposure with 95% CI, in European football during six seasons from 2017/18 to 2022/23.

When the periods before (from season start to 19 November) and after (19 December to the end of the season) the World Cup were analysed separately, the match injury incidence in both periods was similar to what had been reported during these periods in previous seasons. The incidence of training injuries in the period leading up to the World Cup was significantly higher (17%) than in previous seasons (table 1). When muscle injury incidences were analysed during these periods, no significant differences were observed compared with previous seasons (table 1).

Figure 3 shows monthly injury incidences and muscle injury incidences in training and match play compared with the median and IQR of the five preceding seasons. Injury incidences during the 2022/23 season were similar to those in previous seasons. Still, a potential increase in training injury incidences and a decrease in match injury incidences were observed during the World Cup months (November and December).

Figure 3. Total injury incidence and muscle injury incidence, presented as the number of injuries per 1000 hours of exposure, in European football clubs during the 2022/23 season compared with historical data from 2017/18 to 2021/22. The shaded areas represent the IQRs for the period 2017/18 to 2021/22.

The injury incidence of World Cup players during the 2022/23 season was generally lower than that of non-World Cup players, but reached statistical significance only for match injury incidence. When injury incidences in the period before and after the tournament were analysed separately, no differences were identified between World Cup players and non-World Cup players (table 2).

Table 2. Injury incidences and rate ratios comparing World Cup players with non-World Cup players during the 2022/23 season.

	Non-WC players (n=693)	WC players (n=219)	Rate ratio (95% CI)	P value
Full season
Training injury incidence (95% CI)	3.7 (3.3 to 4.0)	3.1 (2.6 to 3.8)	0.86 (0.70 to 1.05)	0.145
Match injury incidence (95% CI)	22.5 (20.4 to 24.8)	18.9 (16.4 to 21.7)	0.84 (0.71 to 1.00)	0.044
Training muscle injury incidence (95% CI)	1.8 (1.6 to 2.1)	1.4 (1.1 to 1.9)	0.77 (0.57 to 1.05)	0.095
Match muscle injury incidence (95% CI)	10.1 (8.7 to 11.7)	11.0 (9.2 to 13.2)	1.09 (0.86 to 1.38)	0.460
Season start to 19 November*
Training injury incidence (95% CI)	3.7 (3.3 to 4.0)	3.1 (2.4 to 4.1)	0.85 (0.63 to 1.16)	0.311
Match injury incidence (95% CI)	22.3 (19.3 to 25.8)	17.5 (14.1 to 21.6)	0.78 (0.61 to 1.01)	0.061
Training muscle injury incidence (95% CI)	1.9 (1.6 to 2.3)	1.5 (1.0 to 2.3)	0.81 (0.52 to 1.25)	0.333
Match muscle injury incidence (95% CI)	10.0 (8.1 to 12.4)	10.1 (7.6 to 13.3)	1.01 (0.71 to 1.43)	0.976
19 December to end of season†
Training injury incidence (95% CI)	3.5 (3.1 to 4.1)	3.0 (2.3 to 3.8)	0.84 (0.63 to 1.13)	0.250
Match injury incidence (95% CI)	23.5 (20.5 to 26.9)	20.2 (16.8 to 24.2)	0.86 (0.68 to 1.08)	0.189
Training muscle injury incidence (95% CI)	1.7 (1.4 to 2.1)	1.2 (0.8 to 1.8)	0.71 (0.45 to 1.12)	0.145
Match muscle injury incidence (95% CI)	10.6 (8.6 to 13.0)	11.9 (9.4 to 15.1)	1.12 (0.82 to 1.53)	0.467

Injury incidence is presented as the number of injuries per 1000 hours of exposure. Text in bold indicates a significant difference.

^*Period from the start of the season to the start of the World Cup.

^†Continuation of the club season after the World Cup.

WC, World Cup.

When the injury incidence for World Cup players in the period before the World Cup was compared with the period after the tournament, no significant differences were identified with corresponding RRs of 0.95 (95% CI 0.65 to 1.38, p=0.777) for training injury incidence, 1.15 (95% CI 0.87 to 1.52, p=0.317) for match injury incidence, 0.78 (95% CI 0.44 to 1.37, p=0.383) for muscle injury training incidence and 1.18 (95% CI 0.82 to 1.70, p=0.376) for muscle injury match incidence.

Of the 219 players selected for the 2022 World Cup, 14 (6%) sustained injuries during the tournament, resulting in continued absence after the event. These injuries aggregated to a total of 362 absence days during the continuation of the club season, representing 1.3% of the total injury absence during the season (26 418 absence days in total) and 2.2% of the injury absence (16 162 absence days in total) during the period following the World Cup.

Discussion

The most important finding of this study was that the injury incidence in European professional club football during the 2022/23 World Cup season was similar to that in previous seasons. This finding contrasts with recent observations from French professional football.⁴ It refutes our hypothesis that the novelty of a mid-season World Cup in November and December would contribute to a distinct increase in injury occurrence during the season.

No major changes in injury incidence during the 2022/23 season

One of the main reasons it was believed that a mid-season World Cup would increase injury occurrence during the 2022/23 club season was that it would lead to match congestion, with the same number of club matches as in any previous regular season being played in a shorter period.² This argument made theoretical sense since several previous reports have shown that match congestion can cause an increased injury occurrence,³ muscle injuries in particular.^{17 18}

As expected, an increased number of matches per month was observed in specific periods of the 2022/23 season, particularly in October, just before the World Cup, and also towards the end of the season in April and May. This increased match congestion did not, however, translate to an increased injury incidence, at least not in matches. Training injury incidence, on the other hand, was slightly higher during the 2022/23 season compared with the aggregate for the five previous seasons, which was mainly due to a lower training injury incidence in the 2017/18 season rather than a sudden increase during the 2022/23 season. Our study contrasts with a recent study on 17 teams in the French Ligue 1, which identified a significantly increased occurrence of injuries during the 2022/23 season compared with the previous 2021/22 season.⁴ However, the incidence of training injuries could not be calculated since training exposure was not recorded, making a direct comparison to our study difficult. Additionally, the study included only the preceding season for reference purposes. In contrast, our study used historical five-season data to smooth out the influence of any between-season or within-season outlier data.

Changes in injury rates during the World Cup months

Match injury incidences during the World Cup months (November and December) appear to be lower than in the preceding five seasons. The most obvious explanation for this difference is that few competitive club matches were played during these months. Previous studies have shown that the incidence of injury in friendly matches is significantly lower than in competitive matches.^{20 21}

A distinct increase in training injury incidences was also shown during the World Cup months. The most plausible explanation for this increase is that the coaching staff increased the training load and/or intensity during this period in response to the lack of match time, thereby avoiding de-training of players who remained with their club teams.²² Increasing the physical demands of training sessions, making them more match-like, could logically also increase the incidence of injuries during the sessions, considering that most injuries occur during high-intensity actions.^{23 24}

Did a two-month World Cup break protect from injury?

There are some potential explanations for why injury incidences during the 2022/23 season were similar to those in previous seasons. First, most players did not participate in the World Cup, and the 1- to 2-month break from competitive matches during the tournament could be considered an extended winter break. Previous studies have shown that teams that are allowed a winter break suffer fewer injuries than teams that are not.^{25 26} It is possible that this ‘enforced’ winter break allowed players suffering from overuse injuries, not yet causing absence from football, to recuperate from these conditions during a less competitive part of the season before their complaints forced them to miss out on any training sessions or matches. Second, it has also been argued that high absolute loads and accumulated fatigue over extended periods can increase injury risks.²⁷ A one to two month break from competitive matches in the middle of the season could potentially reduce the accumulation of fatigue, making players less susceptible to injuries in the later stages of the season.

Are World Cup players less injury prone?

World Cup players were found to have a lower incidence of match injuries before the World Cup compared with their colleagues who did not participate in the tournament. One potential explanation is that being injury-free may be a prerequisite to being selected for a World Cup. An injured player, for obvious reasons, cannot participate in a World Cup. Even if an injury had been resolved before the tournament started, players who have suffered injuries may still be at a disadvantage compared with non-injured players if they have not yet reached their desired level of performance.²⁸ Previous injury is one of the most prominent risk factors for new injuries,²⁹,³¹ and it is therefore not surprising that players who have been less likely to sustain injuries, thus being available and more likely to be selected for the World Cup, continued to have low injury incidence after the tournament. Additionally, it has been argued that players can be prepared for high loads by gradually adapting to them. World Cup players, by remaining injury-free, may have also been accustomed to high loads, making them more resilient to a congested match calendar after the tournament.³²,³⁴

Few World Cup injuries carried over to the club season

The current study showed that only a few World Cup players sustained injuries during the tournament, which continued to cause absence when the tournament was completed. Since the World Cup was played in the middle of the 2022/23 European club season, several European national leagues continued their competitions just over a week after the World Cup final was played. Historically, domestic competitions have begun close to a month after the finals of previous World Cups, which were all played during the off-season.² Logically, this would cause an increased frequency of players still being injured due to injuries that occurred during the 2022 World Cup. To our knowledge, no previous World Cups have been evaluated in this aspect, making it difficult to compare this World Cup to previous editions. Injury incidences in World Cups have, however, been analysed since 2002, showing the 2022 World Cup to have the lowest injury incidence of all tournaments since injury monitoring started.⁶⁸,¹¹ This relatively low injury incidence may be one factor contributing to the fact that only a few players returned from the World Cup to their club teams with continued injury absences.

Methodological consideration

While a large and homogeneous dataset strengthens this study, it also has some limitations. First, team inclusion varied between seasons, with different teams participating in different seasons. This means that there might have been team-related factors affecting the results that we have not been able to consider. Second, a time-loss definition of injury was used. While this approach follows consensus and is the most widely used in epidemiological studies in the field, it also has some drawbacks. For example, injuries that do not cause absence may have been overlooked.³⁵,³⁷ Such injuries may be of special interest when overload was hypothesised to be contributing to increased injury rates, and the collection of such complaints could have strengthened the study further. Third, information about players’ mental health was not included. It has been suggested that a congested match calendar could potentially impact players’ mental health,³⁸ and such information would thus be beneficial. Fourth, it has been shown that training loads are often decreased when match loads increase, and vice versa,^{39 40} and it is plausible that similar load management strategies were implemented in the club teams participating in the present study. More information about the intensity of football exposures could have contributed to a more detailed explanation of how club teams may have changed their training content over the season to compensate for the lack of competitive matches during the World Cup and the match-congested periods before and after.

Conclusion

No major changes in injury incidences were observed during the 2022/23 season compared with previous seasons. The increased incidence of training injuries appeared to be due to a general increase during the study period and a significantly lower incidence during the 2017/18 season, rather than a sudden increase during the 2022/23 season. World Cup players experienced similar injury incidences before and after the tournament, and had a lower match injury incidence before the tournament compared with non-World Cup players. Injuries sustained during the World Cup caused a limited absence during the continuation of the club season.

Data availability statement

No data are available.