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Rehabbing hamstring injuries can be complex

An injury to the hamstring (HS) muscle group — composed of the short and long heads of the biceps femoris (BFI), semitendinosus (ST), and semimembranosus (SM) — is one of the most common occurrences in sports, with a high reoccurrence rate, if not handled properly.

Research demonstrates that most HS injuries occur to the SM and BFI, with weakness being a prime culprit. In the case of ACL (anterior cruciate ligament) repair, surgeons have the option to use a graft from the ST muscle.

From a HS rehabilitative standpoint, whether as a result of an injury to the SM and BFI or the result of harvesting a graft, strengthening in the early phases of rehab should be under the auspices of a physical therapist, who may utilize both open (OKC) and closed (CKC) kinetic exercises, to activate the target muscle group.

According to orthopedic surgeon Scott D. Martin, “in an open-chain exercise, the body is stationary while the limb moves. In closed-chain exercise, the limb is stationary while the body moves. For example, a squat is a closed-chain exercise because your feet stay stationary while your quadriceps do the work. In contrast, a seated leg extension is an open-chain maneuver.”

The HS works in concert with other muscle groups, such as being antagonistic (opposing) to the quadriceps (thigh) on the front side of the leg, and synergistically with the gluteus maximus (GM) — the major butt muscle, and erector spinae (ES) — low back stabilizer.

In order to determine the difference in activity of the ST, SM, GM, and ES muscles during both OKC and CKC exercise, researchers from the Faculty of Sport Sciences, Waseda University, Tokyo, Japan, and Department of Kinesiology, San Jose State University in California, “hypothesized that the ST muscle would work more than the SM and BFl muscles at a deep knee flexion (bend) angle, whereas the latter muscles would work more than the ST at a lower knee flexion angle, regardless of the kinetic change.”

Using EMG (electromyography) to monitor the maximal voluntary isometric capacity at 20 and 40 percent in the leg curl and bridge exercises during knee flexion (bending) angles of 30, 60, 90, and 120 degrees, the researchers sought to isolate which knee joint angle and load would best target each HS muscle. Study participants included sixteen, active males between 18 and 26 years of age.

That’s the ball game, when it comes to the best return on investment of time and energy — eliminating the guess work to hamstring rehabilitation — to get the patient back in the game with the least chance of re-injury.

For the OKC leg curl, the researchers had the participants assume a prone (face down) position on the ground, with cuff weights attached around the ankles and the legs extended. The participant bent the knee(s), bringing the heel toward the butt, limited to the target angle of the bend at the knee.

The CKC bridge had the participant lying on their back with the legs bent to the target angle. The action was to elevate the butt, until the hips were fully extended. The bridge, depending on the angle, also works the GM — a hamstring extensor.

According to the researchers, “the leg curl and hip bridge exercises, with knee flexion angles between 30 and 60 degrees, act to activate the SM and BFl during rehabilitation.”

In addition, “if clinicians treat the ST conservatively during strength training of the hamstrings, such as post-ACL repair, this study recommends both legs exercises – with knee flexion angles between 60 and 120 degrees.”

If therapists are opting to use the leg curl and bridge at the recommended angles for rehabilitation, then we might consider using both in a preventive mode to reduce the risk to a protracted hamstring injury that has sidelined so many athletes.

Consult a physical therapist for guidance.

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