Do you have adequate hip extension?
Running is an integrated and skilled movement. We have
discussed motor patterns and programming in previous posts. Today we briefly
discuss hip extension mechanisms (or lack of) and resultant forces in the lower
limb.
It is common to see running technique with a torso/
trunk that is behind the centre of mass (COM), particularly when fatigue sets
in. At the centre of this is the position of the pelvis and the musculature
acting upon this.
The driving force behind this is almost always poor
pelvic position. This occurs most commonly due to posterior pelvic tilt. Another
position may exist where an anterior pelvic tilt is observed with overly tight (short)
hip flexors disrupting full extension of the hip. For now we will focus on lack
of hip extension in the following two
forms:
· Posterior pelvic tilt (the pelvis is tucked under)
· Anterior displacement of the pelvis (essentially a
posterior pelvic tilt with the pelvis displaced anteriorly fostering a host of
biomechanical faults)
These postures create a nutated (‘tucked under’)
sacrum jamming the ability of the boney innominates to rotate around the sacrum
disrupting full hip extension. A lack of full hip extension will result in a
posterior lean during the stance phase of gait to accommodate lack of range of
motion and resultant weakness. This position decreases demand on the hip
extensors by reducing hip flexion. The result is an increased work on the knee
due to increased knee flexion moments. In this case (reduced hip extension) the
glute max, hamstring and adductor magnus and a host of deep glute stabilisers
decrease their activity due to length tension relationships within the pelvis.
The increased knee moment loads the patella-femoral
joint. Larger forces across the knee joint are due to the eccentric loading as
the quadriceps slows the increased knee moments. These larger angles have been
associated with patella-femoral pain, a leading cause of over use injury in
distance runners.
Lack of hip extension increases overstriding. Overstriding is seen when we land in front of
the bodies COM essentially creating a rear foot strike increasing collision
forces. Dan Lieberman (2010) found this in his correlation between habitually
shod and barefoot runners. The piece of information we don’t have conclusive
evidence for is whether this increased collision force increases injury risk.
The more important factor here is probably not how you land but ‘where ‘ you
land. More research in this area is needed.
Landing outside the COM also puts the hamstring at a
biomechanical disadvantage attempting to decelerate the limb at peak knee
extension just before stance phase. In this position there is a decreased pre
stretch which loses the ability to fully use the stretch shortening cycle
(SSC). This is often termed ‘free energy’ as the serial elastic components
store potential energy in the tendinous structures and myofascial system
(predominantly the ‘slings’* through out the body)
A decrease hip extension may also change the toe off phase
placing increase loads on the calf musculature as it attempts to push off in a
shortened position. Essentially there are larger contractile forces on the calf
with less hip extension.
The typical runners body observed here is one with
large quads and calves and lazy glutes and hamstrings (they have ‘no bum’).
These are injuries waiting to happen in the calves and lumbo-pelvic area.
A further set back of decreased hip extension is lack
of stability and loading through the lumbar spine. A posterior tilt ‘opens’ up
the lumbar spine lengthening the multifidus and deep spinal stabilisers
(rotatores, transversarri, spinales). These protect and stabilise the lumbar
spine. When the length tension relationship is disrupted – the stabilisers
cannot contract, as they do not have enough muscle fibre overlap – they are too
long and weak in this position. Changing the pelvic position towards neutral
and some basic re-education usually helps address this however, depending on
the health of your back it may take some time to recover from this.
On a very practical level this position of running
creates a run that ‘muscles’ and ‘fights’ it’s way through the gait cycle.
There is no free fall or use of the SSC every step accelerates and decelerates
more than it needs to. Increased amount of rotation will find their way into
the gait. This results in a quick onset of fatigue.
If you have the range to get into good hip extension
when running but you don’t do it, it’s probably a biomechanical education
scenario. In other words you need some education on how to clean up your
biomechanics. If you don’t have the range then get your pelvis in the correct
position
Try this; Go for a run and tuck your pelvis under.
What you’ll find is that it decreases your hip extension, creates large rear
foot loading and tightens up the hamtrings. Because your pelvis is in a sense
in front of you, a lean back is the most natural thing to do.
In closing start with the pelvis and you’ll be
surprised with the changes it can achieve!
