We’ve all heard about the importance of the “core” to performance and injury prevention. Today, we will arrive at a particular muscle of the core, but talk more about bones; specifically how pelvic attitude can force compensations throughout the entirety of the rest of the skeletal system. By “attitude” I mean the tilt of the pelvis in an anterior (bucket tipped forward), posterior (bucket tipped backward), or neutral.
While a huge amount of time and consideration can go into the dynamics of the pelvis, for the purposes of this article, we’ll keep it short and simple. Because of the orientation of the femur (thigh bone) inserting into the acetabulum (“socket” in the pelvis), an anterior tilt of the pelvis results in internal rotation and adduction of the pelvis: a “knock-kneed” position. This also results in internal rotation of the tibia (shin bone) and excessive pronation (flattening) of the foot. This position is highly contributory to ACL and MCL injury at the knee, as well as plantar fasciitis and posterior tibialis tendinopathy in the foot/ankle. Looking above the pelvis, that same forward tilt is associated with an increase of lumbar lordosis (arching of the lower back), kyphosis of the thoracic spine (curving of the upper back), and forward head.
Maintaining a neutral pelvis, to permit a neutral lower extremity and spine, becomes an obvious goal for those wishing to maximize their performance and reduce their risk of injury. And while a full-on posterior tilt of the pelvis, can also lead to its own compensations, it is far less common. This is in part because there are only three primary muscles in the human body which can cause a posterior tilt, or more functionally, prevent an anterior tilt: the hamstrings, the glutes, and the rectus abdominis (the “6-pack” muscle of the abs). It’s important to note that the glutes and the hamstrings are the primary hip extensors (moving the thigh bone backwards – as when we run), and cannot both stabilize the pelvis and move the femur. So, what will commonly happen instead, is that the pelvis gets rotated forward, becoming “stable”, and then the rest of the hip extensors available (now typically only the hamstrings) can propel the runner forward. This highlights the importance of maintaining good strength, endurance, and (most importantly) control over the rectus abdominis muscle – the only major muscle left to prevent that anterior tilt and all the negative skeletal movements that might subsequently occur.
At the same time, tightness of the back extensors, the psoas, the iliacus (commonly connected as the “iliopsoas”, or hip flexors), the rectus femoris (the only quadriceps which crosses the knee and the hip) are all quite common, and pull the pelvis into an anterior tilt. Interestingly, “tight hamstrings” sometimes happen simply because the brain is recruiting them to pull that pelvis backward.