Those "Tricky" Hamstrings (Part 3)

So far, we have discussed the consequences of OVER STRETCHING and the role of the NERVOUS SYSTEM in treating and preventing hamstring injuries.  Now it's time to dive in to the ROTATIONAL component of our hamstrings.   We cannot treat the hamstring group in just one plane of motion.  Look at the diagram and notice that there are some hamstring muscles that attach to the inside (medial) side of the knee, and others that attach to the outside (lateral) side of the knee. When working together, the medial and lateral hamstrings will act in a coordinated manner to bend the knee and extend the hip.

 

Individually, the medial hamstrings turn the thigh inward (Internal Rotation or IR) and the lateral hamstrings turn the thigh outward (External Rotation or ER).  This means that the hamstrings are also a crucial player in side-to-side and rotational movements.  On the same lines, the hamstrings will act at the upper attachment at the pelvis.  The medial hamstrings will pull the pelvis back and inward (pelvis IR) and the lateral hamstrings will pull the pelvis back and outward (pelvis ER).  This means the hamstrings also play a crucial role in stabilizing the pelvis, even in rotational movements.

SO WHAT?

It is paramount to understand the rotational role the hamstrings play in order to thoroughly train and prepare this powerful group of muscles.  Rotation of the thigh, shin, foot, pelvis, or spine can bias one side of the hamstrings and put the other on a stretch.   When done intentionally, this can ensure the hamstrings are being thoroughly trained.  However, when there is excess or lack of rotation elsewhere in the chain that is not addressed, there will develop an unintentional imbalance of the medial and lateral hamstrings.

The most common of all the hamstring muscles to be injured is the Biceps Femoris (the long head, which attaches to the outer knee).  This is the only hamstring muscle that also acts as an external rotator (ER). For this reason, the Biceps Femoris is in a lengthened, inefficient position in both a forward (anterior) tilted pelvis and a "relatively" backwards (posterior) rotated pelvis.   As discussed in PART 1, a forward tilted pelvis elevates the pelvic attachment site of all the hamstrings. Additionally, when a pelvis is tilted forward, the Semimembranosus and Semitendinosus have been found to have decreased activity at TERMINAL SWING, as well as at Initial Contact and Midswing.  This means that, on a forward tilted pelvis, the Biceps Femoris is then more active than it's medial counterparts during these phases.  Remember that Terminal Swing is when most hamstring injuries occur.  The other time they occur is at Midswing.

The Biceps Femoris is additionally stressed on a pelvis that is either tilted backwards (or, more likely, "relatively" backwards compared to the opposite pelvis that is forward).  On the posterior (backwards) tilted pelvis, the Biceps Femoris will ALSO be in a lengthened position, because the pelvis bone also rotates the pelvic attachment outward (via acetabular-femoral IR) and the femur IR muscles are overactive and turning the femur in.  The combination of an increased demand on an inefficiently-positioned muscle is a one-two punch.

Semimembranosus and Semitendinosus injuries are more likely to occur on a forward rotated pelvis. On a forward rotated pelvis, the hip ER muscles will become overactive.  At Initial, Mid and TERMINAL SWING, the femur must IR and the Medial hamstrings must work harder to fight against these powerful ER muscles by the time the foot lands. The excessive ER use also holds the femur in a more ER position, lengthening the Semimembranosus and Semitendinosus.  Again, a double-whammy on this group of muscles at Terminal Swing.

ROTATION ABOVE AND BELOW

In PART 2, I mentioned that the foot can affect hamstring function. Foot contact and control have a crucial influence on hip and pelvis rotation. For example, when we land, the femur is in IR and the heel should be turned in (inversion).  The foot should then "unlock" via Eversion  so that appropriate ER of the femur can occur through midstance. An inability to get the off the outside heel during gait will keep your foot "locked" and the femur in IR longer through the gait cycle. Likewise, a lack of Eversion prior to toe off, we will create increased hip IR in order to "fake it". There are consequences for early or too much Eversion, as well.  Here's the main point. If the foot and hip are not on the same page, there will be physical strain and neural confusion at the hamstrings (particularly the "outer hamstring, Biceps Femoris) as they get ready to enter the Swing phase.

In addition, rotation of the thorax above the pelvis will also influence the pelvis and femur rotation from the top down.  There are several muscles that have attachments at both the lumbar spine and pelvis.  If there is something off in the spine, it will affect the position of the pelvis and femur. For instance, the Psoas muscle rotates the thigh outward (femur ER) and rotates the low back to the opposite side. Decreased ability to rotate the upper trunk to the right, will lead to increased low back and pelvis rotation to the right to make up the deficit.  The Left Psoas will be overworking to perform this rotation... additionally creating ER at the left femur.

Another interesting fact is found in a study by Yang, et al, in the Journal of Applied Biomechanics.  They discovered "a key finding that the pelvis and the thorax become out-of-phase with each other as gait velocity increases." See the diagram of their findings below.  You can read the full study here:  Interaction Between Thorax, Lumbar, and Pelvis Movements in the Transverse Plane During Gait at Three Velocities

The problem is that balanced lower body function requires equal and opposite upper body position.  Remember the picture from the running series (on right)?  Maybe this lack of Thoracic rotation compared to Pelvis rotation during increased speeds helps explain why we are more vulnerable to hamstring injuries at faster speeds.  There is less counter-rotation to keep the hamstrings in a good functional position when the speed increases.  Just because this is common, is it actually ideal?  Increasing and coordinating upper body rotation with lower body rotation during faster speeds should be considered in hamstring programs, as well. 

TO SUM IT UP

The hamstrings do more than just flex the knee and extend the hip
Rotation of the femur/pelvis determines which hamstring muscles work harder or become lengthened
The hamstrings are also key stabilizers of the pelvis during weight shift & rotational movement
Foot mechanics and upper trunk rotation play key roles on the timing of hamstring firing patterns
Throughout gait, the hips, pelvis, foot and thorax must all be in the same phase at the same time
Terminal Swing function is set up for success or failure at Midstance