If you're strong, surely you'd have good stable joints.  Strength training improves joint stability - right? This article explores some of the key concepts of Jacqui Clark's Lumbar Spine Workshop that show that this isn't necessarily the case.

Firstly we'd better differentiate between local and global stability.  To get an understanding of the difference it's useful to look at muscle function (Comerford and Mottram, 2001).  While these muscle functions are integrated in "real life", it's useful to have these artificial classifications to understand how to develop a treatment plan.  Local stabilisers such as multifidus and transverse abdominus act to control segmental translation.  When applied to the lumbar spine, think of controlling the axis of rotation of each segment and the facet joints.  The muscles that provide local stability to these joints have been shown to be recruited prior to movement in any direction.  It's important to note that these muscles are not specific to the direction of movement.  Transverse abdominus will normally recruit whether the spine is being subjected to a flexion, extension or a rotation load.  Vastus medialis, a key local stabiliser of the knee is recruited in knee extension and knee flexion.  Also note that these local muscles are low threshold - they are recruited early and under low load.

Global stabilisers have quite a different role.  Let's look at the abdominal obliques and gluteals as examples.  These muscles tend to be oblique as they are well suited to controlling for rotation.  Compared to local stabilisers these muscles are direction specific - they control movement in a specific direction.  They are recruited under low load to assist in controlling movement.

To round off our muscle classifications we need to mention the global mobilisers. These are the big moving muscles spanning multiple joints such as erector spinae, rectus femoris and hamstrings.  These muscles are high threshold muscles recruited mostly at high load.

In muscle dysfunction we typically see a decrease in the activity in local and global stabilisers and an increase in the tone of global mobilisers in an attempt to provide stability.  For example in lubo-pelvic injury it's common to see reduced oblique and gluteal function and a decrease in local stabiliser function with an increase in hamstring, TFL and abdominal bracing.

To correct dysfunction we need to target our treatment to match muscle function.  Local stabilisers require specific low load training to recruite dysfunctional local stabilisers. These muscles will not necessarily return to their low level "buzzing" activity after injury with strength training.  They require specific low load training (Jull et al, 2005; Nudo, 2004; Remple, 2003).  High load training does not effectively recruit these muscles.

To retrain movement control issues, such as forward bending excessively from the lumbar with fixed hips requires skill (motor control) training, not strength training.  Skill training increases the cortical representation of the area in the brain. This enables the patient to understand and feel pelvic and spine positions.

The global stabilisers have an important role to play here.  If the patient can feel and achieve pelvic and lumbar spine positioning with control and under low load then they may be a candidate for strength training.  Global mobilisers are likely to be restricting movement eg. hamstrings, superficial gluteus maximus.  Strength training with loaded squats, deadlifts, bent over rows for this patient would cause the problems to escalate by increasing recruitment of the high threshold global mobilisers and likely result in injury. Stretching and tissue work to reduce the activity of global mobilisers is useful, however with increased activation of local and global mobilisers the mobilisers are able to be down regulated by the body.  Normal day living - even in high performance strength athletes still requires local and global stability at low loads eg. walking, bending over the sink brushing your teeth.  This needs to be prioritised early on.

In conclusion, loading a dysfunctional body without investing in local stability work to increase the activity of dysfunctional local stablisers and correcting any movement control issues can set you up for a painful body with rock hard global mobilisers that are hanging on for dear life.

Jacqui Clark practically applies these concepts and corrective exercises in her Lumbar Spine Workshop held in New Zealand November-December 2011.