Posterior Chain Biomechanics: The Calf
The calf is made up of two muscles (gastrocnemius and soleus) and they play an important role throughout the running cycle. When the foot is first landing on the ground, the calf is tasked to slow down knee flexion and ankle dorsiflexion and foot pronation. The calf is then used to extend the knee and assist in propelling the body forward to the next step. If calf length is limited, increased forces will be absorbed at the knee, foot, and ankle instead of through the muscle itself. This impairment could lead to common running injuries, like stress reactions, shin splints, or plantar fasciitis as well as a number of other issues further up the chain.
Other posterior chain mobility dysfunction may occur as a result of tight hamstrings. The hamstrings are made up of four different muscles (biceps femoris long head, biceps femoris short head, semimembranosus, and semitendinosus). These muscles attach to various locations on the pelvis, thigh bone (femur), and back of the shin (tibia) and functionally act as knee extensors (when the foot is on the ground during running, squatting, walking, etc). Although hamstrings do flex the knee when the foot is not on the ground (think flexing your knee to lift your heel to your butt), this is not their primary function despite what you might read online or in text books. The hamstrings do most of their work when the foot is first loading onto the ground - their job, like the calf muscles, is to slow down the forward momentum of the knee. By decelerating this motion, the knee will stop flexing and extend as the femur moves forward over the tibia.
At the same time the hamstrings are decelerating knee flexion during foot strike, they also work to decelerate the pelvis tilting forward (anteriorly) in space. During late stance phase, the hamstrings serve to help posteriorly tilt the pelvis to drive hip extension and further extend the knee to assist with the foot pushing off the ground. Overly shortened hamstrings lead to excess stress on the knees and low back, primarily during the initial phase of loading onto the foot while walking and running.
Keep in mind that we have only really discussed one plane of motion in the above analysis. The hamstrings actually play a critical role, like all muscles, in all 3-planes of motion.
The glutes are a classic mobility issue for most runners. If you remember from our blog post ‘Dead Butt Syndrome’, the glutes can become relatively inactive due to our culture of sitting and most exercise being limited primarily to the sagittal plane (running, biking, swimming). The glutes and other hip external rotator muscles work together to decelerate the turning in of the femur during the initial loading phase of gait and rotate the femur outward during the late stance phase of gait.
When the glutes are tight, the femur will be unable to turn in properly during foot strike which makes it difficult for the glutes to stretch and gain the potential energy necessary to assist in decelerating ground reaction forces. This chain reaction is necessary to propel the body forward and help as the leg pushes off the ground. Tight glutes also contribute to low back pain more directly by limiting the pelvis’ ability to tilt anteriorly during foot strike as well as to rotate over the femur (hip internal rotation) throughout the later stages of stance phase of gait.
Mobility will be improved with consistent, intentional movements, over and over, day after day. Without this consistency, results will be delayed! It is imperative to continually find time before and after your run or workout to improve posterior chain mobility and decrease your chances for running related injuries and improve your performance.
Dr. Dan Benson, DPT, OCS, FAFS
Forefront Physical Therapy
Belltown & South Lake Union
2720 4th Ave Ste 115
Seattle, WA 98121