Serial Hamstring Strains & Sport: Why Does It Keep Happening?

Anyone who regularly watches, plays, or has played sports probably has heard of a hamstring strain. Strains describe a range of injuries to a muscle or tendon which can vary in severity and type. These can include overstretching of individual or groups of muscle fibers, micro-tearing of fiber bundles, or partial to full thickness tears which can occur in any muscle.

So Why is The Hamstring So Commonly Strained in Certain Sports?

The hamstring is comprised of three different muscles on the back of your thigh, which run from your pelvis to beyond the knee, inserting on the tibia. The largest one sits on the lateral “outer” half and is called the biceps femoris. Two smaller hamstrings run medially (on the inside) and are called the semitendinosis and semimembranosis. To understand why hamstrings are vulnerable to strains you’d have to understand muscle function and fundamental characteristics of the tissue itself.

Pulling vs. Shortening

Muscles typically work hardest when they are asked to slow down a segment vs speed it up. This is because in order to slow down a segment the tissue is required to fire yet continue lengthening. Muscles do not quite work like rubber bands, but for the sake of understanding consider this analogy: when you are pulling back the bands on a slingshot before letting go and “firing”, when are the bands under the most stress — when you are pulling it back or letting it go? More force is required to pull it back than let it go, even though the band is rapidly changing length after letting it go, and only slowly changing length when pulling it back. This is a fundamental elasticity principle that helps explain why muscles can be under the most stress when lengthening (quickly or not) vs shortening quickly.

Primary vs. Secondary Function

The hamstrings collectively work together for two main movement functions: bending the knee (primary) and extending the hip (secondary). While these are the main movement functions, the role the hamstrings play during running and cutting is a bit more complex. Since the hamstrings attach at both the pelvis and tibia (lower leg bone), they actually have to lengthen when you are straightening your knee or flexing your hip (bringing leg in front of your body). Now imaging running; how fast and how often are you bending and then straightening your knee? The hamstrings, being long muscles, undergo rapid changes in length through the repetitious running cycle and work the hardest to slow down the tibia before heel strike, while immediately requiring the knee to bend after contact to repeat the cycle. This means the hamstring is very active throughout running just to manage the knee and tibia. With the hamstring being the secondary mover of the hip, if the primary movers (gluteal muscles / “buttocks”) are either weak or not firing properly, now the hamstrings are further required to manage hip movements. This leave the hamstring to manage tibia position, knee bending, and hip movement while rapidly lengthening and shortening — with no moment to rest in the cycle. Even if the hamstrings are strong, if the demand on them is unbalanced due to deficiencies in other muscles, they can quickly become overworked and eventually strained.

Strengthening the Hamstrings After Injury Isn’t Enough

Often after a hamstring strain, a standard rehab program will target those muscles for increased strengthening to tolerate higher loads to allow return to play. The problem with this approach is that it commonly leads to reinjury of the hamstrings if the underlying issue isn’t addressed. In most hamstring strain cases, it is rarely an isolated hamstring strength issue. In fact, sometimes the hamstrings are actually overdeveloped! Once strength as been restored in the hamstrings after injury, it is important to measure what the other muscles are doing during sports specific movements. If hip musculature is deficient in strength or timing during running and cutting, the hamstring is going to become overworked and likely become reinjured. This is observable with surface electromyography during testing at the hamstrings. It is easy to see a cycle of perpetual hamstring injury with this story. Additionally, joint position and mechanics can greatly impact demand on the hamstring musculature and should also be considered. Using the portable lab, I have measured adolescents and adults who have come to me after multiple hamstring strains and it is very common to see either asymmetric joint movement patterns, deficiencies in quadriceps / gluteal performance, or both. Addressing any underlying identified impairments with appropriate training or exercise programs has led to great outcomes — finally putting chronic hamstring strains in the past!

If you or a friend have problems with reinjuring hamstrings, please reach out for a consult to discuss options!