Rise in hamstring injuries may be linked to professional footballers' relentless schedules: BJSM

Dr Ekstrand and his colleagues explored trends in the number and types of hamstring injuries over the past two decades (2001-2002 to 2021-2022), with a particular focus on the last eight seasons (2014/2015 to 2021/2022). They included 3,909 players from 54 teams in 20 European countries who competed in 21 consecutive seasons. 

The players were all part of the Elite Club Injury Study, which was started by UEFA (Union of European Football Associations) in 1999, with the aim of reducing football injuries and boosting player safety. 

The researchers analysed data collected by the medical teams on the amount of time players spent in training and match play; periods of absence due to injury, illness or other reasons; and type of injury (structural or functional).

Nearly one injury in five linked to hamstring issue

The severity of the injury was classified according to the number of days laid off between injury occurrence and return to match play: slight (none); minimal (1–3); mild (4–7); moderate (8–28); and severe (28+ days). 

Over 21 seasons, 2,636 hamstring injuries were reported during a total of 2,131,561 hours of training and match play: 922 (34 per cent) during 1,787,823 training hours, and 1,714 (66 per cent) during 343,738 match play hours. 

The proportion of these injuries doubled between the first and last seasons, increasing from 12 per cent of total injuries in the first, to 24 per cent in the last, and comprising nearly a fifth (19 per cent) of all 14,057 injuries registered during the study period. 

Similarly, lay-off days caused by hamstring injuries doubled, rising from 10 to 20 per cent between the first and last seasons, and comprising 14 per cent of the total number of lay-off days during the study period. The risk of a hamstring injury was 10 times higher during match play than during training, while the average lay-off period was 13 days.

In general, one player in five missed training or match play because of a hamstring injury in any given season, and a 25-player squad can expect about eight hamstring injuries every season, say the researchers. 

Of all the hamstring injuries, nearly a fifth (475;18 per cent) were recurrences, and early recurrences (325)—within 2 months of return to play—made up more than two thirds (69 per cent) of these. All recurrences were nine times more likely to occur in match play than in training. 

Between 2014/2015 and 2021/2022, time trend analysis revealed a significant increase in the number and severity of hamstring injuries during training. Over the entire study period, most (71 per cent) hamstring injuries were structural, and these were associated with more lay-off days than those for functional injuries, averaging 17 vs six. 

Professional players now work year-round apart from a four to six week break between seasons. Even during the traditional break between seasons, players are often required to undertake pre-season tours which require intercontinental travel [Jan Ekstrand et al]

Conclusion: increasing running speeds could be factor

As they conducted an observational study, Dr Ekstrand and his colleagues acknowledge that their remit did not extend exploring the reasons behind their findings. But, based on 21 years of observations, they suggest a combination of more intensive match play and a crowded fixtures calendar could play a part.

‘The intensity of elite men’s football has increased over at least a period of the years that are included in the current study. Current football practice includes a large volume of high intensity football actions. Professional players now undertake more high-intensity activities per match than they did previously and they also run faster than their predecessors,’ they explain.

‘Professional players now work year-round apart from a four to six week break between seasons. Even during the traditional break between seasons, players are often required to undertake pre-season tours which require intercontinental travel.’

The full version of the article, titled 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 doi 10.1136/bjsports-2021-105407 is available at: https://bjsm.bmj.com/lookup/doi/10.1136/bjsports-2021-105407