A two-season study of English football league clubs has confirmed that hamstring strains are the most common injuries in football, accounting for an average of 90 days and 15 matches missed per club per season and with a significant recurrence rate of 12%.

Player injuries were prospectively reported by club medical staff from July 1997 through to the end of May 1999, including any problem sustained during training or competition that prevented the injured player from participating in normal training or competition for more than 48 hours (not including the day of injury).

Of the 91 clubs that started the study, completed injury records for the entirety of both seasons were attained from 87% in the first year and 76% in the second. The major findings were as follows:

• A total of 796 hamstring injuries were documented during the study period, more than for any other muscle group;
• 94% of these hamstring injuries were strains, with hamstring strains accounting for 12% of total injuries over the two seasons. More than half of these strains involved the biceps femoris muscle;
• The incidence of hamstring strains was higher among Premier League players (28%) than the other divisions (22-26%), perhaps reflecting the increased physical demands of faster-paced games;
• A rate of five hamstring injuries per club per season was observed, with an average of 18 days and three matches missed per strain, resulting in 15 matches and 90 days missed per club per season;
• Nine out of 10 hamstring strains were caused by non-contact mechanisms (running, jumping, turning etc), with 57% of the total sustained during running alone;
• A third of strains were sustained during training and nearly two-thirds during matches. Nearly half of match injuries occurred during the last third of the first and second halves of the match, suggesting fatigue as a factor;
• As expected, goalkeepers sustained significantly fewer hamstring strains than outfield players. Players of black origin sustained significantly more strains than white players and younger players were less prone to strains than their older counterparts;
• The reinjury rate for hamstring strains was 12%, compared with an average reinjury rate for all injuries of 7%.

The researchers, from the Football Association’s Medical Research Programme, believe that the high incidence of hamstring injuries may be partly due to the fact that this muscle group functions over two joints and is therefore subject to stretch at more than one point. Also, the greater proportion of fast-twitch fibres in the hamstring muscles compared with others in the legs and thighs means that they are capable of higher force production.

The hamstrings may be particularly vulnerable to injury during running, the researchers explain, because they have to make a rapid switch from eccentric to concentric functioning during the swing phase, when they are placed under extremely high loads in an elongated position.

Players of black origin may be especially at risk of hamstring strains for anatomical reasons to do with the tilt of their pelvises.

Given the high recurrence rate of hamstring strains, the researchers emphasise the importance of prevention of initial injuries, accurate diagnosis, appropriate management and thorough rehabilitation.

Br J Sports Med 2004;38:36-41