It’s almost that time of year where fall sports are getting ready to fire up. One of the most common injuries we typically hear during this time, especially with NFL teams opening up camp, is the dreaded hamstring strain. Hamstring strains account for 12-16% of all injuries in athletes and have a high rate of reoccurrence. Thomas Michaud, an expert in gait, stated that out of all gait related injuries hamstring strains have the highest rate of reoccurrence with as many as 1/3 of injured athletes suffering re-injury within the first few weeks of return to play. Hamstring strains can really hamper you from having that great season you are looking forward to. The average time lost due to hamstring strain is 18 days, varying between 8 to 25 days, as well as fighting the persistent symptoms and the risk of re-injury. To better understand why this occurs we have to look at the function of the hamstrings, especially its dynamic role.
The hamstrings are made up of 3 muscles: Semimembranosus, Semitendinosus, and the Biceps Femoris. While it is by standards a concentric knee flexor, during the locomotion phase it acts as an eccentric stabilizer of the knee. The semimembranosus and semitendinosus both attach on the medial side (inner) of the tibia, while the biceps femoris attaches on the lateral side (outer) of the leg on the fibia. You can think of them like the reins on a horse helping to decelerate the leg during the swing phase of running and preventing translation of the tibia in the frontal and transverse planes during the stance phase.
In a study looking at the activation of the hamstring muscles during different intensities of running there was significant increase in activation of the hamstrings from 85% to 95% maximum velocity during the late swing phase of running. This correlates with us talking about the role of the hamstrings to decelerate the leg during the swing phase by eccentric contraction, since during extension of the knee we are eccentrically loading the hamstrings.
The Mechanism of Injury
Hamstring strains typically occur during the sprint phase of running, with the biceps femoris usually being the culprit. So how does this all tie together? Hamstring strains usually occur when the hamstrings are being eccentrically loaded (lengthened). The hamstrings are eccentrically loaded during both hip flexion and knee extension. Studies have found that the peak strain of the hamstrings occurs in the terminal swing phase suggesting this period may pose the greatest threat. While this tells us when we are most susceptible to a hamstring strain it doesn’t tell us the underlying variables that increase the risk of injury. The three most common variables that increase the risk for hamstring strains are poor eccentric hamstring strength, poor pelvic positioning/core stability, and decreased activation of primary hip extensors.
Eccentric Hamstring Strength
Poor eccentric hamstring strength has been found in research to be a big player in the risk of hamstring strains. A study of Australian football players found that decreased eccentric hamstring strength was a risk factor for future hamstring strains, while the likelihood of athletes with a previous history of hamstring strains was reduced if an athlete had high levels of eccentric strength. Fatigue of eccentric hamstring strength was another factor found when soccer players performed intermittent running on a treadmill to simulate a soccer game, eccentric hamstring strength decreased with increased work time. The inability to prepare the hamstrings to endure high levels of eccentric load greatly increases the risk of hamstring strain.
Pelvic Positioning and Decreased Hip Extensor Activation
When forward tilting of the pelvis is present it adds a pre-eccentric load of the hamstrings, it brings the ischial tuberosity up affectively lengthening the hamstrings. Core stabilization is affected as well by pelvic position because when the pelvis is tilted forward it inhibits the core muscles such as diaphragm, obliques, and glutes ability to help stabilize the pelvis. This adds more stress to the hamstrings to make up for the core muscles being inhibited and stabilize the pelvis.
When the glutes aren’t firing properly, glute maximums is the primary hip extensor, it causes the hamstrings to take over duties for glute maximums and become the primary hip extensor. This puts even more demand on the hamstrings that are already in charge of decelerating the leg and picking up slack of the inhibited core muscles. That’s a lot of stress and roles for one group of muscles to perform, not to mention not strategically efficient leading to quicker fatigue.
Putting the Puzzle Together
To better understand hamstring strains we have to look at the big picture from the function of the hamstring in their dynamic role to the underlying factors that increase your risk of injury and re-injury. The goals in treatment should be to correct pelvic positioning, increase eccentric strength of the hamstrings, and add a core strengthening program. When proper rehabilitation exercises are performed, the annual re-injury rate for hamstring strains have been shown to drop from 70% to 7.7%. Stay tuned for our post on exercises to add to your routine to help reduce the risk of hamstring strains and re-injury. If you are interested in hearing more, contact our office today for a complementary consultation with one of our highly qualified doctors. TROSS proudly serves the Cottleville, St. Peters, St. Charles, O’fallon, and St. Louis communities.
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