Mike Robertson and I were discussing this study that showed how training the trunk muscles for improved stability resulted in a reduction in hamstring stiffness.  In other words, flexibility improved without stretching the muscles.

To bring you up to speed, here’s the study in a nutshell:

The hypothesis is that increased hamstring stiffness compensates for the insufficient performance of the deep stabilizing muscular subsystem (does anyone smell the TVA bias in the room?).

To test their hypothesis they measure the hamstring stiffness of 30 people using a PKES test (Supine, hip flexed 90 degrees, extend the knee and measure the knee angle).  The subjects spend 2 days learning to perform “isolated, conscious activation of the deep stabilizing muscle subsystem”.  They then perform a variation of a plank with feet elevated in slings (body is horizontal) and a variation of supine hip extension twice a week for 4 weeks.  At the end of four weeks, the hamstring stiffness had decreased (flexibility improved).

Their conclusion:  The results of this study support our hypothesis.

Huh?  How do you figure?

Now certainly the training performed resulted in a reduction in hamstring stiffness which is very interesting (we’ll get to that in a minute), but how did they determine it was the result of an improved deep stabilizing whatever, whatever?

There was no pre-test of the deep stabilizing whatever, whatever.  Sure they spent 2 days learning to consciously activate it, but that doesn’t mean that its function was improved nor dysfunctional in the first place.  They used an integrated exercise that involved all of the abdominal muscles, hip muscles, and other trunk and shoulder muscles.  And there was no post-test of deep stabilizing…well, you get the point.

I’m not saying that they are wrong or right, only that you can’t conclude much more than that the training performed for improved stability reduced hamstring stiffness.  To their credit, they do mention in the second to last sentence that “it is still possible that stability training influenced stiffness of the hamstrings in some other way than by improving action of the deep musculature.”  Well done.  It could have also been improved hip stability or even shoulder stability (yes, there’s a connection)

The interesting stuff…

The point to take away from this is that mobility restrictions aren’t always mechanical tissue related issues.  In other words, stretching isn’t always the answer.

In situations where an individual is faced with a task that exceeds his ability to adequately control posture, balance, or range of motion, it’s not uncommon to see what appears to be a lack of mobility or some form of movement compensation.

This compensation is often a “locking up” of joints, frequently by two joint muscles like the hamstrings, to create stability with a comprise to mobility.  The movement will frequently appear to be uncoordinated or the athlete may seem slow or weak in reacting.  This is not a dysfunction that you can fix with the correct stretching protocol.

The fix requires restoration of stability utilizing a lower level activity that the athlete can control effectively and progressing toward more complex tasks that lead to higher force, higher speed, and higher skill movements.

This also reinforces the importance of observing your athletes in action where they experience and participate in the specific conditions and demands of their chosen sport.

Everything is an assessment.

Bill