Hamstring strain

The hamstrings are a group of three muscles at the back of the thigh: the Biceps femoris, Semitendinosus muscle, and Semimembranosus muscle. They begin at the Ischial tuberosity at the bottom of the pelvis and extend to just below the back of the knee. They perform two actions together: extending the hip backward and bending the knee. During running, they control the leg as it reaches forward and help drive it backward, so they bear greater forces as speed increases.

A strain occurs when a muscle is stretched beyond what it can tolerate, damaging the muscle fibers or the junction between muscle and tendon. Of the three muscles, injuries are reported most commonly in the long head of the biceps femoris. Injury severity is usually classified as grade 1 (damage to some fibers), grade 2 (a partial tear), or grade 3 (a complete rupture). For the general classification of muscle strains, see Muscle strain.

The most typical situation is sprinting at full speed. Just before the foot touches the ground after the leg has reached forward, the hamstrings produce force while lengthening to slow the leg down. Producing force while lengthening is called Eccentric exercise, and this is when the greatest tension is placed on the junction between muscle and tendon.

Other factors commonly discussed include:

• A previous hamstring injury
• Insufficient preparation before exercise (Warm-up)
• Weakness at the back of the thigh relative to the Quadriceps femoris at the front
• Differences in flexibility or strength between the left and right legs
• Sprinting at full speed while fatigued

Acute injuries are broadly discussed as two types.

Sprinting-type. This occurs during running, just before the forward-reaching leg touches the ground. At this moment, the biceps femoris is producing force while lengthening. You may suddenly feel a “pop” or a stabbing sensation at the back of the thigh while running, causing you to slow down or collapse on the spot.

Stretching-type. This occurs when the muscle is stretched to an extreme with the hip deeply flexed and the knee straight, such as when lifting the leg high in ballet or making a sliding tackle in football. This type tends to affect tissue closer to the tendon rather than the muscle belly and is understood to take longer to recover.

Even within hamstring injuries, recovery times and the likelihood of recurrence are reported to differ by type. Remembering the movement that caused the injury can therefore help with subsequent management and return-to-sport planning.

• Sudden, sharp pain at the back of the thigh while running, sometimes with a “pop.”
• More pain when pressing on the area or bending the knee.
• Swelling develops over time, and bruising may spread along the back of the thigh or toward the knee.
• Walking with a limp, with even light jogging becoming difficult.

In everyday language, people may say, “I've pulled my hamstring” or “I feel a pulling sensation at the back of my thigh.”

Recovery time varies greatly depending on the severity and location of the injury. Mild strains resolve relatively quickly, but injuries closer to the tendon or near the ischial tuberosity take longer. Even after a mild injury, the disappearance of pain does not mean that muscle strength and flexibility have fully returned. The usual approach is therefore to progress gradually from walking to light running and then to sprinting.

Hamstring strains are among the sports injuries with a relatively high rate of recurrence. Reports have consistently found that a history of previous injury increases the risk of another injury. A widely used approach is therefore to go beyond simply being pain-free and check that strength and movement have sufficiently recovered before increasing exercise intensity.

• Immediately after the injury — Stop the activity you were doing and avoid painful movements. While the pain settles, maintain movement with gentle walking within a pain-free range.
• Once the pain settles — Begin gentle stretching and strengthening exercises within a comfortable range, and gradually increase the intensity without provoking pain.
• When returning to activity — Progress from walking to light running and then faster running. Increase the load in stages using a Load management approach.
• Prevention — Prepare your body with a Warm-up before exercise. The Nordic hamstring exercise, which trains the muscles at the back of the thigh to produce force while lengthening, is also commonly used.

• Pain severe enough to make walking difficult, or difficulty bearing weight
• A sudden snapping sensation below the buttock, with severe pain when sitting
• Extensive bruising or substantial swelling at the back of the thigh
• Pain that does not improve after several days or is getting progressively worse

These signs may indicate more than a simple pulling sensation, so discuss your condition with a sports rehabilitation professional. Sciatica, Proximal hamstring tendinopathy, and Muscle contusion can also cause pain in a similar location, so it can help to examine both the painful area and its cause.