The hamstrings are a set of muscles located on the back of the thigh that span from the ischium bone of the pelvis to the tibia and play an important role in the movement of the human body. The hamstring muscle group allows knee flexion and, consequently, actions such as walking, running and countless other movements in the lower extremities.

The importance of the hamstring muscles in the lower locomotive body means that injuries to this area are common in sports that require explosive movements. Hamstring injuries account for between 12-17% of all injuries in professional men’s soccer, as well as being the type of injury with the highest chance of relapse.

The number of hamstring injuries has experienced a clear increase in recent years. In view of this problem, UEFA developed a study¹ describing the incidence of hamstring injuries and the workload in professional men’s football over the last 21 seasons (from 2001/02 to 2021/22). They also sought to verify the validity of previous studies in reporting the upward trend in this type of injury. At the same time, the study was used to compare the predominance of injuries to the biceps femoris, semimembranous, and semitendinosus, as well as classifying them by whether they are structural or functional injuries.

Over the 21 seasons covered in the study, the medical team reported 2,636 hamstring injuries in a 2,131,561-hour time period. Of these injuries, 922 (34%) occurred during training, while the remaining 1,714 (66%) occurred during match time.

Of all the injuries located in the hamstrings, 475 (18%) were the result of a relapse. Most of these (325, 69%) are considered early relapses, as they occurred less than two months after the first injury.

Doubled incidence

The most important finding is the upward trend in hamstring injuries. At the start of the study, they accounted for 12% of all injuries, while last season the percentage had risen to 24%, doubling its incidence. This upward trend has also been reflected in the recovery periods for said injuries, since the proportion of days absent went from 10 to 20%.

The turning point appears in the 2014/15 season, when there was a significant increase in hamstring injuries both in training and on match days.

To explain this higher percentage of hamstring injuries, the study proposes two hypotheses. Firstly, that the intensity in men’s professional football has increased in recent times. Footballers now perform more high-intensity actions per game, and they also run faster than their predecessors. This hypothesis is supported by the fact that 61% of hamstring injuries occur while the player is running or sprinting.

Secondly, the increase in international travel and matches has also had a direct impact. The calendar has more and more matches, decreasing the number of rest days for the footballers, who work throughout the year, except for the 4-6 weeks of holiday between seasons. Even this period is being compromised due to pre-season tournaments, which have, more frequently over the last few years, required intercontinental travel. This relentless demand for trips and games limits pre-season training sessions, which are highlighted as a reducing element in the risk of injury.

Prevalence of structural injury

Between the 2011/12 and 2021/22 seasons, a total of 1,843 injuries were reported. Most (1,819) could be classified as hamstring injuries according to the Munich muscle injury classification system, while the remaining 24 could not be classified.

The vast majority of these injuries (1,312, 71%) were classified as structural injuries, characterised by longer recovery times than functional injuries. The average sick leave time for structural injuries is 17 days, and 6 days for functional ones.

The most recurrent mechanism of injury in the cases analyzed was running or sprinting, with a percentage of 62% in structural lesions and 51% in functional lesions. It is also worth noting that approximately 50% of hamstring injuries in matches happened in the last 15 minutes of each half.

Of the total number of injuries reported since the 2011/12 season, the vast majority were located in the biceps femoris, accounting for 1,054 of the cases, with 761 occurring during matches.

There is an especially striking change in the results when we compare the proportion of structural and functional injuries between the seasons from 2007-2011 with those between 2011-2018. In the first period, only 30% of structural injuries were reported, while in the second, the percentage rose to 72%. This change corresponds to the improvement in the quality of MRI scanners. Up to 2012, images were obtained using 1.0 T and 1.5 T scanners, while now 2 T and 3 T magnets are used, meaning the image is more likely to be classified as grade 2 (structural) than grade 1 (functional).

Sources

¹ Ekstrand J, Bengtsson H, Waldén M, et al. (2022). Hamstring injury rates have increased during recent seasons and now constitute 24% of all injuries in men’s professional football: the UEFA Elite Club Injury Study from 2001/02 to 2021/22. Br J Sports Med Epub. doi:10.1136/ bjsports-2021-105407