4 Risk Factors for Hamstring Injury

Have you ever pulled a hamstring? Do you know someone who has? Chances are you answered 'yes' to at least on of these. Several risk factors have been identified, some of which are obvious even to the novice, and some which require a little more skill. Below is a list of 7 factors:

PREVIOUS INJURY

• After examining over 500 amateur players, injured players have been shown to be two to six times more at a risk of sustaining a new hamstring injury. Recurrent hamstring strains have been shown to result in significantly more time lost than first time hamstring strains. 
• Considering the length of a muscle, there is a point at which it is able to produce the most forceful contraction. Graphically, this is the highest point on the length tension curve. Brockett et al., showed that in the previously injured hamstring, when compared to controls, the peak seems to shift to the left. This shift in the length-tension curve suggests that peak hamstring torque occurred at a significantly shorter muscle length, meaning is possible that when an athlete sustains a hamstring strain they potentially return to play with weakness at longer muscle lengths. This predisposing them for a second hamstring strain during the eccentric terminal sprinting movement. 

Image courtesy of FIFA.com

WEAK HAMSTRINGS: EARLY OR LATE? 

• While we know that most hamstring injuries incurred in soccer happen during the sprint cycle, it remains unclear which part of the cycle. Some of the literature supports the early stance phase or while others points to the late swing phase. In the former case, proponents suggest it is during this phase in which the muscle absorbs the most force as a result of high ground reaction forces (GRF). The laws of physics tell us that for every action, there is an equal and opposite reaction. GRF is basically the forced 'produced' by the ground in response to the force applied by the sprinting athlete. Given that the amount of force applied into the surface when sprinting is several times that of the athlete's body weight, it is reasonable to assume that this is a potential cause for injury for the hamstring, whose function is to absorb the the energy. 
• Studies involving the Achilles tendon in sprinting, and patella tendon in jumping and hopping show that the forces are much higher in the concentric stance phase as opposed to the eccentric swing phase and researchers suggest that this may apply to the hamstrings as well. 
• Other studies demonstrate that in the swing phase of the sprint cycle, where the hamstrings eccentrically contract to absorb the kinetic energy and slow the lower limb, they are under significant load. Of particular interest is the musculotendinous area, which is inherently at great risk for injury, because the hamstrings are in a lengthened state. This occurs when the hip is in flexion and the lower leg moves into extension, thus lengthening the two joint hamstring muscle over both articulations upon which they act. From this perspective, eccentric weakness of the hamstrings poses a risk for injury. 

Germany vs Spain.

STRENGTH IMBALANCE

• Legendary sprint coach Charles Francis said, "If an athlete is in a sport where leg strength and power are not required to be maximal, then testing hamstring/quadriceps strength at low to moderate speeds may have some relevance... We looked at five or six of our top athletes [sprinters] and discovered that the average ham/quad ratio was more in the order of 125-130:100." 

IMPROPER WARM UP

• How much time do you spend warming up before a game? Even a recreational one? FIFA's medical research team has found that warming up purposefully can be highly effective, reducing the incidence of injury by up to 50%. See the "11+" program here.
• Poor hamstring flexibility- in a study, it was been shown that soccer players are less flexible than a control group, and that soccer players do not stretch sufficiently.

England National Team warms up. 

TREATMENT

Schmitt et al., proposed a new concept for the rehabilitation and prevention of hamstring reinjury. They suggested the following 3-phase approach:

PHASE ONE

• Immediately following the injury, the basics should be observed. The focus at this stage is to protect the injury while minimizing losses range of motion (ROM) and strength. The RICE principle will be sufficient- Rest, Ice, Compress, Elevate. 
• At 48 hours, the athlete may begin submaximal isometric strengthening. These should be completed as a set of isometric knee flexion contraction at 30, 60, and 90 degrees of knee flexion by placing the injured limb on top of the into opposite limb and contracting the strained hamstring.
• The hamstring should not be stretched into a painful range at this time but available hip and knee ROM should be maintained. 

PHASE TWO

• The objective of this stage is to prepare for the athlete for sport specific movements. Of particular importance are the progressive regaining of strength throughout the ROM and improving neuromuscular control of the hips and pelvis.
• The athlete may begin to strengthen both concentrically and eccentrically at this time. Eccentric training can be achieved by performing exercises such as the straight leg deadlift,
• Single leg windmills.
• To complete an eccentric single leg windmill the patient stands with the uninjured leg on a chair or fixed surface and reaches down in a diagonal plane while keeping stance leg straight and maintaining a neutral spine. (Figure 2), 
• Nordic hamstring exercise. 
• The Nordic hamstring exercise is performed by having the clinician hold the patient's feet while in tall kneeling. The patient slowly falls forward while maintaining neutral hip posture until he or she can't control descent any longer and then pushes back into starting position with upper extremities. (Figure 3).
• The athlete should also be able to jog both forward and backward without pain at a moderate speed at this point.

Single leg deadlift

PHASE THREE

• Rehabilitation focus at this stage is on functional movements and eccentric strengthening in the lengthened state. Plyometric and sports specific training may be initiated as well as advanced balance exercise.
• At the completion of this stage the athlete should have full strength throughout the range of motion and should be able to confidently perform all sport related tasks without limitation.

Below is the the reference and link to the article.

REFERENCE

Brandon Schmitt, B., Tyler, T., McHugh, M (2012). Hamstring Injury Rehabilitation and Prevention of Reinjury Using Lengthened State Eccentric Training: A New Concept. The International Journal of Sports Physical Therapy. Volume 7, Number 3, Page 334