Risk Factors for Lower Extremity Muscle Injury in Professional Soccer: The UEFA Injury Study

TLDR: Intrinsic factors found to increase muscle injury rates in professional soccer were previous injury, older age, and kicking leg.

Abstract: Background:Muscle injury is the most common injury type in professional soccer players. Despite this, risk factors for common lower extremity injuries remain elusive.Purpose:To evaluate the effects of various player- and match-related risk factors on the occurrence of lower extremity muscle injury in male professional soccer.Study Design:Cohort study; Level of evidence, 2.Methods:Between 2001 and 2010, 26 soccer clubs (1401 players) from 10 European countries participated in the study. Individual player exposure and time loss muscle injuries in the lower extremity were registered prospectively by the club medical staffs during 9 consecutive seasons. Hazard ratios (HRs) were calculated for player-related factors from simple and multiple Cox regression, and odds ratios (ORs) were calculated for match-related variables from simple and multiple logistic regression, presented with 95% confidence intervals (CIs).Results:There were 2123 muscle injuries documented in the major lower extremity muscle groups: adduc...

Figures

Table 1. Nature and circumstances of lower extremity muscle injuries in professional soccer players.

Figure 1. Seasonal distribution of lower extremity muscle injury rates (injuries/1000 h of total exposure). A lower rate was found during preseason (July-August) compared to the competitive season (September-May) for adductor (rate ratio [RR] 0.78, 95% CI 0.61-0.98, P = .03), hamstring (RR 0.48, 95% CI 0.39-0.60, P < .001), and calf injuries (RR 0.57, 95% CI 0.40- 0.80, P = .001), while quadriceps injury rates were higher during preseason (RR 1.40, 95% CI 1.11-1.75, P = .004).

Table 4. Simple analysis of match related risk factor variables for lower extremity muscle injuries from logistic regression.

Table 3. Significant risk factors for lower extremity muscle injury from multiple Cox regression and logistic regression analyses.

Table 2. Simple analysis of player related risk factor variables for lower extremity muscle injuries from Cox regression.

Full text

Risk Factors for Lower Extremity Muscle
Injury in Professional Soccer: The UEFA
Injury Study
Martin Hägglund, Markus Waldén and Jan Ekstrand
Linköping University Post Print
N.B.: When citing this work, cite the original article.
Original Publication:
Martin Hägglund, Markus Waldén and Jan Ekstrand, Risk Factors for Lower Extremity
Muscle Injury in Professional Soccer: The UEFA Injury Study, 2013, American Journal of
Sports Medicine, (41), 2, 327-335.
http://dx.doi.org/10.1177/0363546512470634
Copyright: SAGE Publications (UK and US)
http://www.uk.sagepub.com/home.nav
Postprint available at: Linköping University Electronic Press
http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-89743

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RISK FACTORS FOR LOWER EXTREMITY MUSCLE INJURY IN
PROFESSIONAL SOCCER: THE UEFA INJURY STUDY

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ABSTRACT
Background: Muscle injury is the most common injury type in professional soccer players.
Still, risk factors for common lower extremity injuries remain elusive.
Purpose: To evaluate the effects of various player and match related risk factors on the
occurrence of lower extremity muscle injury in male professional soccer.
Study Design: Cohort study.
Methods: Between 2001 and 2010, 26 soccer clubs (1401 players) from 10 European
countries participated in the study. Individual player exposure and time loss muscle injuries in
the lower extremity were registered prospectively by the club medical staffs during nine
consecutive seasons. Hazard ratios (HRs) were calculated for player related factors from
simple and multiple Cox regression, and odds ratios (ORs) were calculated for match related
variables from simple and multiple logistic regression, presented with 95% confidence
intervals (CIs).
Results: There were 2123 muscle injuries documented in the major lower extremity muscle
groups; adductors (n=523), hamstrings (n=900), quadriceps (n=394), and calf (n=306).
Injuries to the adductors (56%, P = .015) and quadriceps (63%, P < .001) were more frequent
in the kicking leg. Based on multiple analysis, having a previous identical injury in the
preceding season increased injury rates significantly for adductor (HR 1.40, 95% CI 1.00-
1.96), hamstring (HR 1.40, 95% CI 1.12-1.75), quadriceps (HR 3.10, 95% CI 2.21-4.36), and
calf injuries (HR 2.33, 95% CI 1.52-3.57). Older players (above mean age) had an almost
two-fold increased rate of calf injury (HR 1.93, 95% CI 1.38-2.71), but no association was
found in other muscle groups. Goalkeepers had reduced injury rates in all four muscle groups.
Match play on away ground was associated with reduced rates of adductor (OR 0.56, 95% CI
0.43-0.73) and hamstring injuries (OR 0.76, 95% CI 0.63-0.92). Quadriceps injuries were

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more frequent during preseason, while adductor, hamstring and calf injury rates increased
during the competitive season.
Conclusion: Intrinsic factors found to increase muscle injury rates in professional soccer were
previous injury, older age, and kicking leg. Injury rates varied during different parts of the
season, and also depending on match location.
Key Terms: adductor, hamstring, quadriceps, calf, muscle strain
What is known about the subject: Muscle injury is the most common injury type in
professional soccer players, and lower extremity injuries comprise more than 90% of muscle
injuries. Several intrinsic risk factors have been suggested in the literature, but results are
conflicting, and extrinsic risk factors have scarcely been investigated.
What this study adds to existing knowledge: Previous identical injury was consistently
found to be a risk factor for lower extremity muscle injury. In addition, previous injury to
other muscle groups also increased injury rates, a finding not previously reported in soccer.
This study also identified significant extrinsic risk factors for injury including part of the
season, and match characteristics, with varying injury rates depending on match location and
type of competition.

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INTRODUCTION
Muscle injuries are very common in soccer, representing up to 37% of all time loss injuries at
men’s professional level.
1,10,20,24
In a recent study in European professional soccer it was
shown that a club with a 25 player squad can expect 15 muscle injuries each season and that
muscle injuries accounted for more than one-fourth of all lay-off time from injuries.
9
Injuries
to four major muscle groups of the lower extremity - adductors, hamstrings, quadriceps, and
calf - comprise more than 90% of all muscle injuries in professional soccer.
9
In order to establish prevention programs it is important to identify risk factors associated
with the occurrence of injury, preferably using analysis accounting for the multifactorial
etiology of injury.
33
Some, but not all, intrinsic risk factors identified for lower extremity
muscle injury include previous injury,
1,13,14,21
older age,
1,21,26
poor flexibility,
1,3,15,26,27,42
and
decreased muscle strength or strength imbalances,
7,8,13,15
but results from different studies are
contradictory. Extrinsic risk factors have only been scarcely investigated, but match play has
consistently been associated with an increased rate of muscle injury.
9,13,14,21
Fatigue may be a
component in the occurrence of muscle injury, since some studies have found that muscle
injuries occur more frequently towards the end of matches.
9,23
Finally, it has been shown that
various match factors, such as the type of match, match location (home or away) and match
result may influence general injury rates in professional soccer,
5,12,22
but sub-analyses of
lower extremity muscle injuries have not been reported.
The purpose of this study was to evaluate the effects of various player (intrinsic) and match
related (extrinsic) risk factors on the occurrence of lower extremity muscle injury in male
professional soccer.