Epidemiology of Muscle Injuries
A muscle injury is defined as a “traumatic distraction or overuse injury to the muscle leading to a player being unable to participate fully in training or matches.” Muscle injuries represent almost one-third of all time-loss injuries in male elite football and account for more than one-quarter of all layoffs following injuries. 1, 2
There are many different types of muscle injury, and a wide range of terminology is used to describe them. Muscle injuries have to be classified in different groups in order to be able to provide a prognosis regarding recovery times and rehabilitation, and large sample sizes are needed in scientific studies if authoritative statements are to be made.
This chapter is based on 4,500 muscle injuries suffered by more than 3,500 players in elite teams across 18 European countries. All examples and statistics are taken from data collected via the UEFA Elite Club Injury Study between 2001 and 2012.
3.1.1 How Common Are Muscle Injuries?
Fig. 3.1 On average, a player sustains a muscle injury every other season. 1
Thigh muscle injuries
Five or six hamstring and two or three quadriceps injuries per season
Groin muscle injuries
Four or five per season
Calf muscle injuries
One or two per season
3.1.2 Injury Risk during Matches
The risk of sustaining a muscle injury is six times higher during matches than during training (8.7 injuries per 1,000 match hours, compared with 1.4 injuries per 1,000 training hours). 1
Two-thirds of all hamstring injuries suffered by players occur during matches—compared with half of all calf muscle, hip/groin, and quadriceps injuries.
3.1.3 Muscle Injuries and Age
Fig. 3.2 The risk of sustaining a muscle injury during a match for different age groups.
3.1.4 Variations in Injury Risk during Matches
Thigh muscle injuries tend to occur more frequently toward the end of each half of a match (see ▶ Fig. 3.3). 1, 2, 3 A similar tendency is seen for hip/groin injuries in the first half, while the risk of suffering a calf injury is fairly constant until the last 15 minutes of the match, when the injury risk increases substantially.
Fig. 3.3 Distribution of muscle injuries during a match.
3.1.5 Variations in Injury Risk over a Season
▶ Fig. 3.4 shows the distribution of muscle injuries over a season for teams with an autumn–spring season. Muscle injuries are more common during the period from August to April, when most league matches are played. In January, when many leagues have a winter break and fewer matches are played, the risk of suffering thigh and hip/groin injuries (but not calf injuries) is reduced ( ▶ Fig. 3.5a, b).
Fig. 3.4 Distribution of the most common muscle injuries over an autumn–spring season (injuries/1000 hours of total exposure)
Fig. 3.5 (a, b) In January, when fewer matches are played, the risk of suffering thigh and hip/groin injuries, but not calf injuries, is reduced.
3.1.6 Developments in Injury Risk over the Last Decade
▶ Fig. 3.6 shows injury risk over a period of 11 seasons for teams participating in the UEFA Champions League. The injury risk for all muscle injuries (as well as the most common subtypes) was fairly stable over that period, with only small differences between seasons. This would suggest that any changes in rules, athleticism, or teams’ playing styles during that period did not affect injury risk.
Fig. 3.6 Muscle injuries suffered by UEFA Champions League teams between 2001 and 2012.
3.1.7 Artificial Turf
Ekstrand et al 4 compared injury risk in male elite football between matches played on third-generation artificial turf and matches played on natural grass in terms of the injury risk for male elite-level football. The study found a lower risk of lower-extremity muscle injuries during matches played on artificial turf compared with matches played on natural grass (6.2 vs. 3.7 injuries per 1,000 match hours).
3.1.8 Location of Muscle Injuries in Football Players
As can be seen in ▶ Fig. 3.7, 92% of all muscle injuries in football affect the lower extremities of the body. The hamstrings (37%), quadriceps (19%), adductors (23%), and calf muscles (13%) are the most common locations for injuries. At elite level, hamstring injuries are the most common injury type, representing 12% of all injuries.
Fig. 3.7 Location of muscle injuries in football players.
3.1.9 Contact versus Noncontact Situations
As many as 96% of all muscle injuries occur in noncontact situations. Only 4% are sustained as a result of player-to-player contact ( ▶ Fig. 3.8).
Fig. 3.8 Only 2% of muscle injuries sustained during matches are the result of foul play in the view of the referee.
3.1.10 Severity of Muscle Injuries and Length of Layoffs
As can be seen in ▶ Fig. 3.9, between 39 and 46% of all muscle injuries are of moderate severity, causing a player to miss between 8 and 28 days of training/matches. Between 9 and 13% of muscle injuries are more severe, causing the player to miss more than 28 days. In general, thigh and calf injuries are more severe than hip/groin injuries.
Fig. 3.9 Severity of muscle injuries.
Notes: “Minimal” = player misses 1 to 3 days of training/matches; “mild” = player misses 4 to 7 days; “moderate” = player misses 8 to 28 days; “severe” = player misses more than 28 days.