Pretty much everyone has now grasped the importance of hip mobility, but are we going about assessing and addressing it in the right way? A huge amount of emphasis has been placed on the role of restrictions in the hip flexors, justifiably in the large majority of the population, but deficits in internal rotation (IR) are often overlooked. In this article we’ll outline why IR is so important.
Why Is Internal Rotation Important?
Normal kinematics of the leg require the femur to internally rotate within the hip capsule. IR is necessary to some degree to be able to walk, run, squat and perform pretty much every functional movement you can think of. Given that running or jumping movements, the basis of the majority of sports, require only a limited range of motion, a hip internal rotation deficit (HIRD) is not always noticeable. Where a HIRD does become a problem is during movements that require either deep hip flexion or trunk rotation; these articulations require a significant amount of IR to be performed correctly. If the body doesn’t have the necessary IR to complete the movement then other structures in the body are forced to compensate. Ideally, we’re looking for athletes to have about 45o of IR although the majority can cope with around 35o.
Joint centration is the term used to describe the optimal alignment of joints. Proper joint centration diminishes friction caused by the motion of the joint, reducing overall wear and tear, as well as allowing forces to be transferred in the most efficient way. Think of joint centration a bit like a wheel on a car – if the centre of rotation is aligned with the centre of the plate then it will deliver the most efficient performance. If this central position becomes misaligned then the wheel won’t spin correctly and may cause subsequent mechanical problems. The muscles around the hip should serve to keep the head of the femur in a centrated position within the hip capsule allowing for free and effortless rotation, a concept called force closure. If muscles don’t function properly, such as when the IR muscles become short and tight, then this can lead to reduced force closure and suboptimal centration.
Centration and Proprioception
If you haven’t already then check out some of Charlie Weingroff’s articles explaining the ‘core pendulum theory’, he talks through this concept far more succinct and detailed manner than I can.
Full mobility is needed for the joint to effectively recognise its neutral, or default, location. When we have a restriction in place however, this ability becomes impaired. A HIRD effectively works to shift what the joint recognises as its neutral position into external rotation, often exacerbating the initial losses of IR.
Full mobility also allows for optimal feedback to the nervous system, this is necessary for sending appropriate signals to the surrounding muscles; the body needs to be able recognise a range of motion to in order stabilise effectively within it. Losses in range of motion due to a HIRD impair the body’s ability to control itself in conditions when it is put into IR, such as during knee valgus (where the knee collapses inwards). Problems of this manner become magnified under fast, chaotic conditions, such as during running and cutting movements in team sports.
As we’ve touched on, movements requiring deep hip flexion (i.e. squats) or rotation require a significant amount of IR to be performed correctly. The most common compensations we’ll see during these movements are excessive pronation at the feet (feet rolling inwards) and knee valgus. These two compensations effectively ‘cheat’ the range of motion by reducing the amount of IR necessary to complete the movement. When performing rotational movements, such as the golf swing, over-rotation of the lumbar spine is also a likely compensation.
Asymmetries between the left and right hip are common in a large percentage of the population, this can also lead to rotation of the lumbar spine during non-rotational movements such as squats.
Faulty Movement Patterns = Injury
I’m sure it comes as no surprise to you that these sorts of compensations often lead to injury. The risk of HIRD related injuries is greatest in rotational athletes due to the speed and sheer volume of faulty movement patterns their bodies are subjected to. The lower back is the most prolific site of injury but loss of IR has also been implicated knee, ankle and groin injuries.
Next time we’ll look at how to assess IR properly and give you some advice on how to go about restoring any losses in range of motion.