Hamstring injuries are the most common injury in sports and are particularly devastating in the Premier League: they have accounted for an astounding 41 per cent of all player injuries in the 2015-2016 campaign.

In the Premier League the monetary cost of injury is as abrasive as the injuries themselves; teams spent an estimated 198 million pounds on injured players in 2014-2015, a 19% increase over the previous 5 seasons. Teams would much rather pay players to perform on the pitch rather than nurse injuries on the sideline.

This group of three muscles, which stretch from the pelvis down to the back of the knee, are the driving force for many of our basic motions, like walking, running, and jumping. Composed of the semitendinosus, the semimembranosus, and the biceps femoris, the hamstring allows the hip to extend and the knee to flex. The mechanics of these motions are the basis for many explosive movements, making the hamstring one of the most important muscles in sports such as soccer, track and field, basketball, rugby, and American football.

The biceps femoris is the largest of the three muscles in the hamstring. By firing and relaxing this muscle, the lower leg can swing out and back, providing the astounding speed of the Gareth Bales of the world. While it serves as the engine for this kind of high-speed movement, the biceps femoris is the weak link in this motion, making it especially susceptible to injury.

Research suggests that hamstring injuries typically occur during eccentric loading, when the lower leg kicks out, and the muscle is susceptible to excessive force. In more severe cases, the tendon can pull off the bone entirely, though this is more common in high-speed running than it is in football.

Quite simply, this muscle wasn’t designed to power sprints. As humans, we evolved as joggers so that we could follow herds over large distances, not run 100 meters in under 10 seconds. As a result, the hamstring is prone to overactivity, which is why soccer players and sprinters regularly face hamstring issues during their careers. This is rather common in the Premier League thanks to the nature of football and a dense schedule that includes a myriad of other concurrent competitions.

Currently, there are 24 players from 13 different teams sidelined by a hamstring issue, 8 of whom will be out for at least another 4 months. Alexis Sanchez headlines this list, having missed nearly 4 weeks of action after suffering a hamstring strain on November 29th against Norwich City. Unfortunately, the total tally for the season is much larger and includes players who have already returned from earlier injuries, like familiar stars Wayne Rooney and Sergio Aguero.

Hamstring injuries are as costly as they are ubiquitous. With an average recovery time of 6 weeks, an injury can often cost a team over 1 million pounds along with much-needed victories. Sergio Aguero cost Manchester City his weekly wage of 240,000 pounds throughout the duration of his injury from early October to late November, totaling a bill of over 1.5 million pounds. City, who were at the top of the standings at the time of his injury, surely missed their leading goal scorer during their descent to 3rd while he was out.

Even teams without a highly-paid star end up paying a high price: Newcastle United, with 4 players out due to hamstring issues, is paying over 85,000 pounds a week for these sidelined players, which is equivalent to over 11% of their weekly payroll. By factoring in the additional time necessary for players to regain their fitness, hamstring injuries are a hefty financial drain.

In an effort to prevent these damaging injuries, Kitman Labs focuses on known risk factors associated with hamstring injuries.

Studies in professional soccer have reported that these injuries tend to take place at the end of each half, when players are most fatigued. Fatigue has been associated with decreased eccentric strength which leads to shortened stride cycles during running. The hamstring must then generate the same force with shorter muscle fibers, resulting in an increased load on the muscle and thus a higher risk of injury.

The Premier League has acknowledged the role of sport science in curbing the negative effects of injury. It launched the Elite Player Performance Plan three years ago, with injury prevention a key component in the development of domestic players. However, much of the research has focused on assessing the causes of injury, while predictive analysis and identification of risk factors of injury have not yet gained traction in the Premier League.

In short, football players rely heavily on their hamstrings, and the nature of the sport makes hamstring injuries undesirably common. However, an intelligent and comprehensive injury prevention approach can easily make these injuries all the less familiar, reducing the staggering amount of time players lose and the substantial financial burden on the Premier League.