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The hamstrings are a group of muscles at the back of the thigh. They include the biceps femoris, semitendinosus, and semimembranosus. The Hamstrings group play a key role in knee joint flexion and hip extension and are involved in almost all of human movements; from walking to running, as well as many other physical activities. As a result, hamstring strain injuries are one of the most common muscular injuries, and observed across a host of team sports.
These injuries have an impact on individual athletes and also large financial and performance implications, especially in elite sports such as football (7) with the substantial time lost from training and matches in 29% of all injuries sustained (12). The financial cost of this is estimated to be a staggering €280,000 per hamstring strain injury (5).
Figure 1: The Hamstrings muscle-group.
It is thought that the occurrence of hamstring strain injuries is due to the combination of high forces with rapid muscle lengthening actions such as we see in high-speed running (6). In the late swing phase, the hamstrings rapidly change from acting eccentrically (decelerating the extended knee) to performing concentrically (supporting hip extension), which places them in a more susceptible elongated position under high mechanical stress. 90% of hamstring strain injuries are non-contact, which may in part be due to an ever-increasing metabolic demand of team sports combined with a higher proportion of matches spent running at high speed (3). Download our sports physio ebook here.
Hamstring strain injuries are typically graded medically from Grade 1 to Grade 3. A grade 1 diagnosis is usually a mild pull or strain and pain typically lasts a few days. A grade 3 tear however, can take several months to recover from. Grade 1 tears are the most common and usually a sudden pain and tenderness is felt, and it is painful during movement. Severe grade 3 tears are very painful and are normally accompanied by a popping-like sensation at the time of injury.
The primary recovery strategy is to rest the leg and try to avoid taking big strides or pushing too hard, too soon. Other strategies such as keeping the leg elevated and short periods of ice and compression may help speed up recovery. The real key is not returning to sport and training too early, and slowly building up running based activities once pain and tenderness has subsided.
“The financial cost of hamstring strain injuries are estimated to be €280,000 per occurrence”
There are a number of established risk factors for hamstring strain injuries. Some of these we cannot modify such as advancing age, with older players suffering from a greater risk of injury. Previous hamstring strain injury is also a major risk factor.. The long head of the Biceps Femoris muscle has the highest risk of both injury and re-injury (11).
Re-injury typically results in longer periods of recovery than first-time incidences, highlighting the need to improve current prevention and rehabilitation strategies to reduce initial and subsequent hamstring strain injuries.
The good news is that there are things we can do as coaches or athletes to help reduce the risk of getting hamstring strain injuries in the first place. For example, we can develop our eccentric strength, especially at longer muscle lengths. We can also try to avoid big increases in high-speed running training load too (load management). You should consider implementing exercises based on how our muscles fibres are aligned (known as our muscle architecture) such as prescribing Nordic hamstring exercise (Nordic Curl) or “Nordics”.
Nordic Curl strength training has been proposed as a method to prevent hamstring strain injuries (1). The Nordic Curl is the most widely researched eccentric training exercise. Large-scale soccer Nordic Curl interventions have been reported to reduce both first-time occurring hamstring strain injuries (13) and recurrent injuries (9) making it an exercise of particular interest.
Demonstration of Nordic Hamstring Curls
The Nordic Curl is an eccentric only exercise, placing load on the hamstring muscles whilst they are lengthening, which produces proposed beneficial adaptations in eccentric strength and muscle architecture. The Nordic Curl can either be performed using high tech equipment to measure muscle force production or simply completed with a partner/coach to clasp around the ankles.
With the Nordic Curl, it is important to gradually build up the number of repetitions and sets over time, starting with as few as 2-3 repetitions.
Using Output to track data on nordic curls
As with any eccentric-based training, you can expect some DOMS after the first few sessions. The focus should be performing the contractions slowly and controlled throughout the movement with an emphasis on technique, trying to keep the hips square. Another consideration is that more recent evidence suggests similar adaptations and reduction in hamstring strain injury risk can be achieved with much lower training loads (2 sets of 4 rep’s)(4,10).
From a programming perspective, it is important to try and limit the number of Nordics in periods where there are lots of high-speed running or intense periods of match play to avoid unnecessary fatigue and increase injury risk, this should also be a considering for coaches on when to programme Nordic Curl into an athletes’ training programme (8). The Nordic Curl is an eccentrically overloading exercise and therefore should be progressed by increasing the “active” range of motion you can achieve. Your aim should be to increase how far you can lower yourself towards the ground while maintaining tension in the hamstring i.e. how far you can go before you “flop” onto the ground.
The hamstrings are one of the most commonly injured muscle groups in sport, and can be very costly injuries for both the individual and team. We can never truly eliminate the possibility of injury, but we can modify and reduce the known risk factors.
Hopefully, you now understand how hamstring injuries occur a bit better, and more importantly, have the knowledge of some easy interventions you can include in your program to reduce the risk of sustaining a hamstring strain injury.
The Output // Capture Nordics feature assesses range of active motion, rep duration and angular velocity of movement (control) rep by rep to allow for biofeedback and longitudinal tracking with a single wearable sensor. Learn more about Output and our all-in-one testing and tracking system.
Download our sports physio ebook for expert advice on injury risk mitigation, rehab strengthening, hamstring injuries & more.
Dr. Tom Maden-Wilkinson is an established researcher in Neuromuscular Physiology. He completed his PhD at Manchester Metropolitan University examining the age related changes in skeletal muscle as part of the EU-funded myoage project.
Upon completion in 2013, Tom moved to Loughborough University as a teaching fellow in Exercise Physiology, contributing to teaching across the undergraduate and postgraduate sports and exercise science programmes.
Tom joined Sheffield Hallam University in 2017 as a Lecturer in Sports and Exercise Science, with his teaching focus in Exercise Physiology. In addition, consults with leading professional sports teams including Sheffield United in the area of injury prevention, with particular focus on hamstring injury reduction.
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