Integrating core stability into functional movement has long been one of those un-talked about subjects where the assumption is that prerequisite loading in other non-functional positions is then transferred into a loaded environment.  The model used to explain this is the classic model of motor learning described by Posner & Fitt’s in the late 1960’s, which describes three stages of motor learning:

The Cognitive phase

The Associative phase

The Autonomous phase

This model repeatedly surfaces in the physiotherapy rehabilitation literature as an framework for the sequential loading working towards functional tasks.  It should be pointed out that there are several other theories of motor learning which do not necessary follow this paradigm, but it also serves a dual purpose in the clinical environment, as interventions at the early phases using this strategy tend to be low load and therefore minimal risk / reduced likelihood of provocation.

However, there is an equally strong argument for the massive sensory bombardment, which occurs from using functional positions as a way to stimulate specific muscle activity.  Historically, the difficulty in clinical practice is to ascertain whether the target muscle groups are actually being recruited as part of a global functional movement pattern.  This undoubtedly remains the significant clinical challenge.

Some of the recent trends in athletic training involve the use of functional exercise programs, which try to replicate functional demands.  If we look at the frequent reports of symptom provocation from patients, there are some very familiar aggravating factors, which I think we would all recognise.

Sweeping & Hoovering

Carrying shopping

Walking the dog

Accessing car boots

Working in overhead positions

Twisting or reaching

It is clear from evaluating these positions that there is a change in the relationship between the thorax, the pelvis and the intervening lumbar spine and therefore some degree of mobility must accompany the necessary “stability” to counteract loading.

Because segmental rotation in the lumbar spine is very limited (estimated at 2º – 3º in each direction per segment) it would appear biomechanically that the majority of rotation must occur from the thoracic spine and the hips.  It is tempting to speculate that any impaired mobility in these areas maybe a significant driver to rotational pressures through the lumbar spine causing tissue sensitivity.

If we look at control of the lumbar spine during function from that perspective, the role of the oblique musculature (both abdominal and spinal) could be considered as “anti-rotation” muscles whose role is to minimise the stresses distributed to the Lumbar segmental structures.  In that situation the limbs and torso become the external “drivers” forcing load on the core..

Using this model to replicate function there are two key principles of loading.

1)    Asymmetrical stance

2)   Altering the loading segment (driver).

In reality this means that evaluating trunk stability needs to be assessed in conjunction with asymmetric limb loading which is more akin to normal activities of daily living.

Clinically, this means using positions such as:

Asymmetrical squat

Stride stance

Lunge

Single leg stance

as variations in the start position and combining this with variations in the loading force (driver), either using arms, torso or legs.  The degree of difficulty, hence risk of injury, is related to the magnitude of load with arms being the lowest, legs being second and torso being highest.

Whilst visual observation is how most of us rely on accessing the quality of movement there is certainly a limit to what can be achieved.  The big clinical decision is whether we can use load or speed of motion as the next level of exploration/provocation to see if we can elicit a breakdown in control.  Obviously this needs to be weighed up against the vulnerability of the pathology.
So from a practical perspective it is quicker and easier to initiate functional rehabilitation strategies as the prime intervention for low back pain patients unless their level of irritation contra-indicates or they do not tolerate the level of loading associated with function. Patients in that category may then self-select for lower loading regimes as an intermediate stage.

The alternative, and one which has become pervasive in recent years, is to work through a multitude of phases which may not particularly challenge the patient in a way that is relative to function, although appear deficient from the perspective of musculoskeletal control and ideal movement patterns. The well known phrase “Paralysis from Analysis” springs to mind.

Enjoy the clinical challenge.

David

© David for PhysioDigest - an educational resource for the musculoskeletal rehabilitation community, 2009. | Permalink | 2 comments | Add to del.icio.us
Post tags: core, core stability, low back pain, lunges, motor learning, movement impairment syndromes, physiotherapy, single leg stance, squats, transversus abdominis, trunk control

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The link between hamstring strains and poor core stability is frequently casually referred to in rehabilitation and strengthening conditioning literature.  In fact it appears that there is no injury these days that is not associated with impaired “core stability”!

Has it taken over from excessive pronation as the ubiquitous explanation for intrinsic overuse injuries?

However, rarely do we see discussed the postulated mechanisms between impaired trunk control and potential hamstring overload. Here we will consider these hypotheses, the clinical testing methods and rehabilitation strategies to address these functional control deficits.

Mechanism of hamstring overload in “core” instability.

The basic premise of impaired trunk controls involvement in hamstring overload is that compromised proximal trunk control (muscular control above the pelvis) leads to a compensatory overstrain of muscles more distant in the chain, in this case muscles attaching to the lower end of the pelvis.  The analogy of a triangle standing upside down is a useful visual concept to explain this phenomenon.  In this situation we have the hamstrings posteriorly and the quadriceps anteriorly acting with the knee as a point of fixation and trying to balance the pelvis in an antero-posterior direction, almost like reins horse riding.

Importantly the control requirement is not entirely in an antero-posterior direction i.e. a sagittal plane but is in fact all 3 planes of motion:

Sagittal Plane

Coronal Plane

Transverse Plane.

However, it is easier to consider in each individual plane and build up the elements.

Simultaneous Concentric & Eccentric Loading

So the concept of excessive hamstring activity in order to balance the pelvis “from below up” is complicated by the fact that the hamstring muscle group crosses two joints – namely the hip and knee and in many sporting situations there are  simultaneous but different movements occurring at the hip and knee.  This is thought to predispose the hamstrings to alternating patterns of concentric and eccentric activity which maybe required simultaneously depending on the position of the respective hip and knee.

Primary & Secondary Hip Muscle Function

The situation is further compounded by the frequent clinical observation of impaired hip joint extension function i.e. inhibition of the prime one joint hip extensors- gluteus maximus in particular.  Vladimir Yanda described this many decades ago as part of the “cross pelvic” syndrome and although this was reported in a context of tight hip flexors causing secondary gluteal inhibition, the clinical observation in my experience is just as frequent in patients without tight hip flexors – (as measured by Thomas test).

So What?….

So the practical implication of this scenario is an increased loading through the hamstrings by combining both a stability and a mobility challenge.  If we explore this further in terms of functional consequences for muscle recruitment this is often evident as a poor coordination of hip extension (as measured in Yanda’s prone hip extension test).  Here the prone patient is asked to extend the hip an inch off the supporting surface and the clinician observes for the pattern of motion.  First one is looking for the timing of contraction between glutes and hamstrings on the lifting leg with the hypothesis being that the gluteus maximus should initiate the hip extension pattern followed closely by the hamstrings.  In regards to the torso contribution, the proximal pelvis needs to be stabilised in order to allow the 15 to 25kgs of leg to be lifted.  In the presence of  hamstring substitution for gluteus max and compromised trunk control this leg extension is often accompanied by a hyper- lordosis of the lumbar spine and then associated anterior pelvic tilt.  This represents a shift in compensation above the pelvis where the movement of hip extension is enhanced by excessive contribution of lumbar lordosis and paraspinal muscle activation.  A critical point to bear in mind with this movement pattern is that lumbar lordosis associated with paraspinal hyperactivity has the complicating effect of relative inhibition of the anterior abdominal wall, which perpetuates the cycle of global core instability.

Clinical Solution

Previous posts outlined the sequence of progressions for proximal trunk control in this plane.  I don’t need to reiterate them here but follow the link provided for further explanation.  One of the most useful clinical exercises/tests is what I often refer to as tri- bike hip extension.  In this position the patient is in a crouched kneeling position (as a triathlon bike rider) with one leg trailing back behind.  The trailing knee is then bent and the test/exercise is to lift the leg by driving the heel towards the ceiling.  Most importantly – the lower the crouch position the greater the degree of difficulty on lift.

I find this an extremely potent test for evaluating hip extensor function and it also yields good information about trunk stability and compensatory strategies but more on that  another time.

P.S. When patients cramp in the hamstring, doing this exercise, you can bet your bottom dollar they are still trying to use the hamstring as opposed to gluteus maximus to execute this movement.  In that event one needs to revert to a less challenging position.

Enjoy the clinical challenge.

David

© David for PhysioDigest - an educational resource for the musculoskeletal rehabilitation community, 2009. | Permalink | No comment | Add to del.icio.us
Post tags: Biceps femoris, clinical measurementm core stability, gray cook, Hamstring Flexibility deficits, hamstring rehabilitation, Hamstring strain, hamstring treatment, low back pain, movement patterns, multifidus, muscle tone, peter o'sullivan, saggittal plane mechanics, Semimembranosis, Semitendinosus, Shirley Sarhmann, strength testing, transversus abdominis

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