Karolina Kristenson

Injuries affect team performance negatively in professional football: an 11-year follow-up of the UEFA Champions League injury study

Background The influence of injuries on team performance in football has only been scarcely investigated. Aim To study the association between injury rates and team performance in the domestic league play, and in European cups, in male professional football. Methods 24 football teams from nine European countries were followed prospectively for 11 seasons (2001–2012), including 155 team-seasons. Individual training and match exposure and time-loss injuries were registered. To analyse the effect of injury rates on performance, a Generalised Estimating Equation was used to fit a linear regression on team-level data. Each teams season injury rate and performance were evaluated using its own preceding season data for comparison in the analyses. Results 7792 injuries were reported during 1 026 104 exposure hours. The total injury incidence was 7.7 injuries/1000 h, injury burden 130 injury days lost/1000 h and player match availability 86%. Lower injury burden (p=0.011) and higher match availability (p=0.031) were associated with higher final league ranking. Similarly, lower injury incidence (p=0.035), lower injury burden (p<0.001) and higher match availability (p<0.001) were associated with increased points per league match. Finally, lower injury burden (p=0.043) and higher match availability (p=0.048) were associated with an increase in the Union of European Football Association (UEFA) Season Club Coefficient, reflecting success in the UEFA Champions League or Europa League. Conclusions Injuries had a significant influence on performance in the league play and in European cups in male professional football. The findings stress the importance of injury prevention to increase a teams chances of success.

Fewer ligament injuries but no preventive effect on muscle injuries and severe injuries: an 11-year follow-up of the UEFA Champions League injury study

Background Limited information is available on the variation in injury rates over multiple seasons of professional football. Aim To analyse time-trends in injury characteristics of male professional football players over 11 consecutive seasons. Methods A total of 1743 players comprising 27 teams from 10 countries were followed prospectively between 2001 and 2012. Team medical staff recorded individual player exposure and time loss injuries. Results A total of 8029 time loss injuries were recorded. The match unavailability due to injury was 14% and constant over the study period. On average, a player sustained two injuries per season, resulting in approximately 50 injuries per team and season. The ligament injury rate decreased during the study period (R2=0.608, b=−0.040, 95% CI −0.065 to −0.016, p=0.005), whereas the rate of muscle injury (R2=0.228, b=−0.013, 95% CI −0.032 to 0.005, p=0.138) and severe injury (R2=0.141, b=0.015, 95% CI −0.013 to 0.043, p=0.255) did not change over the study period. In addition, no changes in injury rates over the 11-year period were found for either training (R2=0.000, b=0.000, 95% CI −0.035 to 0.034, p=0.988) or match play (R2=0.282, b=−0.015, 95% CI −0.032 to 0.003, p=0.093). Conclusions The injury rate has decreased for ligament injuries over the last 11 years, but overall training, match injury rates and the rates of muscle injury and severe injury remain high.

Regional differences in injury incidence in European professional football.

The objective of this study was to investigate regional differences in injury incidence in mens professional football in Europe. A nine‐season prospective cohort study was carried out between 2001–2002 and 2009–2010 involving 1357 players in 25 teams from nine countries. Teams were categorized into different regions according to the Köppen–Geiger climate classification system. Teams from the northern parts of Europe (n = 20) had higher incidences of injury overall [rate ratio 1.12, 95% confidence interval (CI) 1.06 to 1.20], training injury (rate ratio 1.16, 95% CI 1.05 to 1.27), and severe injury (rate ratio 1.29, 95% CI 1.10 to 1.52), all statistically significant, compared to teams from more southern parts (n = 5). In contrast, the anterior cruciate ligament injury incidence was lower in the northern European teams with a statistically significant difference (rate ratio 0.43, 95% CI 0.25 to 0.77), especially for noncontact anterior cruciate ligament injury (rate ratio 0.19, 95% CI 0.09 to 0.39). In conclusion, this study suggests that there are regional differences in injury incidence of European professional football. However, further studies are needed to identify the underlying causes.

Lower Injury Rates for Newcomers to Professional Soccer A Prospective Cohort Study Over 9 Consecutive Seasons

Background: No study has investigated whether newcomers to professional soccer have a different injury rate than established players. Purpose: The primary objective was to investigate whether being a newcomer to professional soccer influences injury rates. The secondary objective was to evaluate whether playing position and player age influence injury rates. Study Design: Cohort study; Level of evidence, 2. Methods: Twenty-six soccer clubs, with 1401 players, were followed prospectively over 9 consecutive seasons between 2001 and 2010. Club medical staff recorded time-loss injuries and soccer exposure on an individual level. Cox regression analyses were used to evaluate associations between time-loss injuries and time in professional soccer, playing position, and age. Results: In total, 6140 injuries and 797,389 hours of exposure were registered. A decreased general injury rate was observed for newcomers (n = 116) compared with established players (n = 3091) (hazard ratio [HR], 0.77; 95% confidence interval [CI], 0.61-0.99). In contrast, newcomers had a higher rate of fractures (rate ratio [RR], 1.77; 95% CI, 1.05-2.97), especially stress-related bone injuries (RR, 2.68; 95% CI, 1.08-6.69). Using goalkeepers as a reference, all outfield playing positions had significantly higher adjusted injury rates: defenders with an HR of 1.91 (95% CI, 1.64-2.24), midfielders with an HR of 1.78 (95% CI, 1.53-2.07), and forwards with an HR of 1.82 (95% CI, 1.55-2.14). Using players aged ≤21 years as a reference, the overall adjusted injury rate increased with age, with a peak injury rate among players aged 29 to 30 years (HR, 1.44; 95% CI, 1.24-1.68). Conclusion: Newcomers to professional soccer had a lower general injury rate than established players but a higher rate of stress-related bone injuries. Being a goalkeeper was associated with lower injury rates than all outfield playing positions. Injury rates increased with age, a pattern that persisted after adjusting for playing position and match exposure.

THE NORDIC FOOTBALL INJURY AUDIT: HIGHER INJURY RATES FOR PROFESSIONAL FOOTBALL CLUBS WITH THIRD-GENERATION ARTIFICIAL TURF AT THEIR HOME VENUE

Background Previously, no difference in acute injury rate has been found when playing football on artificial turf (AT) compared with natural grass (NG). Aim To compare acute injury rates in professional football played on AT and NG at the individual player level; and to compare, at club level, acute and overuse injury rates between clubs that have AT at their home venue (AT clubs) and clubs that have NG (NG clubs). Methods 32 clubs (AT, n=11; NG, n=21) in the male Swedish and Norwegian premier leagues were followed prospectively during the 2010 and 2011 seasons. Injury rate was expressed as the number of time loss injuries/1000 h and compared with rate ratio (RR) and 99% CI. Results No statistically significant differences were found in acute injury rates on AT compared with NG during match play (RR 0.98, 99% CI 0.79 to 1.22) or training (RR 1.14, 99% CI 0.86 to 1.50) when analysing at the individual player level. When analysing at the club level, however, AT clubs had a significantly higher acute training injury rate (RR 1.31, 99% CI 1.04 to 1.63) and overuse injury rate (RR 1.38, 99% CI 1.14 to 1.65) compared with NG clubs. Conclusions At the individual player level, no significant differences were found in acute injury rates when playing on AT compared with NG. However, clubs with AT at their home venue had higher rates of acute training injuries and overuse injuries compared with clubs that played home matches on NG.

Role of illness in male professional football: not a major contributor to time loss

Background There are limited data on the nature, type and incidence of illness in football. Previous studies indicate that gastrointestinal and respiratory tract illnesses are most common. Aim To describe the incidence and burden of illness in male professional football. Methods Over the 4-year study period, 2011–2014, 73 professional football teams in Europe participated, with a total of 1 261 367 player-days recorded. All time-loss illnesses were recorded by the medical staff of each club. A recordable illness episode was any physical or psychological symptom (not related to injury) that resulted in the player being unable to participate fully in training or match play. Results A total of 1914 illness episodes were recorded. The illness incidence was 1.5 per 1000 player-days, meaning that, on average, a player experienced an illness episode every second season, with a median of 3 days absence per illness episode. Severe illness (absence >4 weeks) constituted 2% of all illnesses. Respiratory tract illness was the most common (58%), followed by gastrointestinal illness (38%). Respiratory tract illness, gastrointestinal illness and cardiovascular illness caused the highest illness burden. Conclusions The illness incidence among male professional football players is low compared with the injury incidence. We found that the highest illness burden was caused by illness to the respiratory tract, gastrointestinal tract and cardiovascular system.

No association between surface shifts and time-loss overuse injury risk in male professional football

OBJECTIVES To investigate frequent surface shifts and match play on an unaccustomed surface as potential risk factors for injury in Scandinavian male professional football. DESIGN Prospective cohort study. METHODS Thirty two top-division clubs (16 Swedish, 16 Norwegian) were followed during seasons 2010 and 2011. The influence from (1) number of surface shifts (between artificial turf and grass) during five-match sequences, and (2) match play on an unaccustomed surface (other surface than on the home venue) on subsequent overuse injury risk was evaluated with generalized estimating equations (GEE). GEE results are presented with risk ratios and 95% confidence interval (CI). Injury rate was expressed as time loss injuries/1000h, and compared between groups with a rate ratio and 95% CI. RESULTS No association was found between the number of surface shifts and subsequent overuse injury risk (risk ratio 1.01, 95% CI 0.91-1.12). Furthermore, no difference was seen in subsequent overuse injury risk after match play on unaccustomed compared with accustomed surface (risk ratio 1.04, 95% CI 0.78-1.38). Grass clubs (grass installed at home venue) had a lower match injury rate when playing away matches on artificial turf compared with away matches on grass (rate ratio 0.66, 95% CI 0.40-0.89). CONCLUSIONS This study showed no association between surface shifts or playing matches on an unaccustomed surface and time-loss injury risk in professional football, suggesting that clubs and players can cope with such surface transitions.

Injuries in male professional football : a prospective comparison between individual and team-based exposure registration

Methodological considerations of football injury epidemiology have only scarcely been described. The aim of this study was to evaluate the inter‐rater agreement in injury capture rate and injury categorization for data registered in two different prospective injury surveillance audits studying the same two Norwegian male professional football clubs for two consecutive seasons, 2008–2009. One audit used team‐based exposure (TBE) recording and the other individual‐based exposure (IBE). The number of injuries recorded and corresponding injury rates (injuries/1000 h exposure) were compared between audits. Cohens kappa and prevalence‐adjusted bias‐adjusted kappa (PABAK) coefficients were calculated for injury variables. Of 323 injuries included, the IBE audit captured 318 (overall capture rate 98.5%, training 98.9%, match 97.8%) and the TBE audit 303 injuries (overall capture rate 93.8%, training 91.4%, match 97.1%). Agreement analysis showed kappa and PABAK coefficients regarded as almost perfect (> 0.81) for 8 of 9 injury variables, and substantial (ƙ 0.75) for the variable injury severity. In conclusion, the capture rate for training injuries was slightly higher with IBE recording, and inter‐agreement in injury categorization was very high.

The influence of climate type on injury epidemiology in european professional football

Background The influence of different weather conditions on injury risk has only been scarcely investigated. Objective The objective was to study the influence of climate type on injury epidemiology in mens professional football in Europe. Design Prospective cohort study. Setting Mens professional football from nine European football associations. Participants 24 clubs followed over a varying number of seasons from 2001/2002 to 2008/2009. Assessment of risk factors The assessed risk factor was the climate type according to the Köppen-Geiger Climate Classification System. This system is divided into five climate types based on the average monthly temperature and precipitation. The dominating climate types in Europe are the Mediterranean, the Marine West Coast (MWC), the Humid Continental, and the Subarctic types. Main outcome measurements The main outcome measure was the difference in time-loss injury incidence between clubs with Mediterranean (MED) and MWC climate types expressed as a rate ratio (RR) with 95% CI. Results Excluding one club belonging to the Humid Continental climate type, there were 16 clubs in MWC group (61 team-seasons) and seven clubs in the MED group (40 team-seasons). The MED group had significantly lower incidence of training (3.5 vs 4.4/1000 h, RR 0.79, 95% CI 0.72 to 0.86) and match (25.5 vs 29.1/1000 h, RR 0.88, 95% CI 0.81 to 0.94) injuries. There were no differences for severe injuries (RR 0.95, 95% CI 0.82 to 1.09), strains (RR 1.05, 95% CI 0.95 to 1.15) or sprains (RR 0.89, 95% CI 0.78 to 1.02). However, the incidence of anterior cruciate ligament (ACL) injury was higher (0.087 vs 0.042/1000 h, RR 2.07, 95% CI 1.10 to 3.90) in the MED group, especially for non-contact ACL injuries (0.083 vs 0.012/1000 h, RR 6.72, 95% CI 2.53 to 17.83). Conclusion Clubs with a Mediterranean climate type had lower injury risk in general, but a substantially higher risk of non-contact ACL injury.

Community-level football injury epidemiology: traumatic injuries treated at Swedish emergency medical facilities

Background Despite the popularity of the sport, few studies have investigated community-level football injury patterns. This study examines football injuries treated at emergency medical facilities using data from three Swedish counties. Methods An open-cohort design was used based on residents aged 0-59 years in three Swedish counties (pop. 645 520). Data were collected from emergency medical facilities in the study counties between 1 January 2007 and 31 December 2010. Injury frequencies and proportions for age groups stratified by sex were calculated with 95% confidence intervals (95% CIs) and displayed per diagnostic group and body location. Results Each year, more than 1/200 person aged 0-59 years sustained at least one injury during football play that required emergency medical care. The highest injury incidence was observed among adolescent boys [2009 injuries per 100 000 population years (95% CI 1914-2108)] and adolescent girls [1413 injuries per 100 000 population years (95% CI 1333-1498)]. For female adolescents and adults, knee joint/ligament injury was the outstanding injury type (20% in ages 13-17 years and 34% in ages 18-29 years). For children aged 7-12 years, more than half of the treated injuries involved the upper extremity; fractures constituted about one-third of these injuries. Conclusions One of every 200 residents aged 0-59 years in typical Swedish counties each year sustained a traumatic football injury that required treatment in emergency healthcare. Further research on community-level patterns of overuse syndromes sustained by participation in football play is warranted.