The following letter was sent to one of the professional physical therapy
groups. Since it focused on the rather trendy cuurent fad of “core
stabilisation”, I thought that this discussion would also be of value here.
Far too many self-proclaimed authorities on back pain, trunk stabilisation
and core stabilisation are proliferating some rather dubious beliefs about
these topics and it about time that some far more cautious science were
applied to them.
Here is the original letter:
<< I’ve just been awarded a research bursary and am planning to investigate
the possible link between hamstring strength and core trunk stability. I’m
planning to measure concentric/eccentric hams strength intially, send
subjects off to do hams strength work, transversus abdominus strength work
and placebo exercises. I’ve been able to get lots of literature re hams
strength, transversus abdominus (mainly Hodges, Jull and Richardson) and hams
injury prevention. What I haven’t been able to get is much information on
hamstring/muscular trunk control interaction. Anybody out there able to point
me in the right direction? >>
Here is my response:
***Just a small point about which I have written before – how does one assess
“core stability” statically or dynamically under conditions in which
peripheral stabilisation does not play a significant role in the overall
stabilisation process or confound the results? For instance, if one wishes
to assess “core stability” in a standing position, then how do we rule out
the major role played by the lower extremity musculature in the process?
Moreover, stability is not necessarily a result of adequate strength, but the
amount of “strength”, force or torque exerted at crucial stages of joint
action throughout any given movement. If someone produces inappropriate
patterns or timings of motion, then, no matter how strong a given muscle may
be, then stability will be severely compromised. This point often seems to
be forgotten in many studies of relationship between injuries and muscle
strength. Though the intrinsic strength of a muscle may be adequate in the
execution of a given task, it may not be utilised efficiently in that or
other tasks.
Moreover, if strength is adjudged to be adequate as estimated by static or
isokinetic tests in a given action, this does not imply that strength under
other conditions will be adequate. We simply cannot ignore the vital fact
that strength is not only the result of muscle action, but of neuromuscular
facilitation in response to specific stimulation in a given motor task. It
is not valid to extrapolate findings from isolated joint testing to a process
as multifactorial as dynamic stabilisation.
In this regard, articles such as the following can be very revealing:
Zajac FE & Gordon MF(1989) Determining muscle’s force and action in
multi-articular movement Exerc Sport Sci Revs 17: 187-230
Andrews JG (1985) A general method for determining the functional role of a
muscle J Biomech Eng 107: 348-353
Andrews JG (1982) On the relationship between resultant joint torques and
muscular activity Med Sci Sports Exerc 14: 361-7
What does all of this imply for the researcher? Well, it means that the
research protocol, and possibly the title of the project, needs to be devised
very carefully to take these problems into account. One has to be especially
careful as to how one defines and measures “stability”, especially the
“stability” of a portion of a dynamically linked system. So far, I am not
very convinced that many researchers are adequately addressing this problem -
maybe you could take a significant step forward to rise above the
perpetuation of some dubious traditional and relatively unchallenged
hypotheses. Best wishes in your task!
Mel Siff
Denver, USA
