Rehabilitating Low Back Disorders - Fundamentals and Assessment Tools for Occupational Ergonomics - page 459

“Sufficient stability” is a concept that involves the determination of how much muscular stiffness is
necessary for stability together with a modest amount of extra stability to form a margin of safety. Inter-
estingly enough, given the rapid increase in joint stiffness with modest muscle force, large muscular
forces are rarely required. In our recent papers, stabilization exercises were quantified and ranked for
muscle activation magnitudes together with the resultant spine load. 35 (Quantification of individual
tissue loads in the spine is a complex procedure and an issue outside the constraints of this article —
the interested reader is directed to Reference 28.) Furthermore, Cholewicki's work 14 has demonstrated
that sufficient stability of the lumbar spine is achieved, in an undeviated spine, in most people with
modest levels of coactivation of the paraspinal and abdominal wall muscles. This means that people,
from patients to athletes, must be able to maintain sufficient stability in all activities — with low, but
continuous, muscle activation. Thus, maintaining a stability “margin of safety” when performing
tasks, particularly the tasks of daily living, is not compromised by insufficient strength but rather
insufficient endurance. We are now beginning to understand the mechanistic pathway of those studies
showing the efficacy of endurance training for the muscles that stabilize the spine. Having strong
abdominals does not necessarily provide the prophylactic effect that had been hoped for — but
several works suggest that endurable muscles reduce the risk of future back troubles. 7
20.5 A Philosophy of Low Back Exercise Prescription
Many traditional notions that exercise professionals consider to be principles for exercise prescription,
particularly when dealing with the low back, may not be as well supported with data as generally
thought. A review of the efficacy of traditional exercise versus stabilization programs both identified
and motivated a re-examination of conventional thought (summarized in Reference 31). For example,
there is a widely held view that sit-ups should be performed with bent knees, but it is becoming apparent
that the resultant spinal loading (well over 3000 N of compression to a fully flexed l-spine) suggests
sit-ups are not suitable for most people at all — other abdominal challenges are more effective and
safer. Other examples include: contrary to the belief of many, adopting a posterior pelvic tilt when per-
forming many types of low back exercise actually increases the risk of injury by flexing the lumbar joints
and loading passive tissues; having stronger back and abdominal muscles appears to have no prophylac-
tive value for reducing bad back episodes — however, muscle endurance has been shown to be protective;
greater lumbar mobility leads to more back troubles — not less 7 ; and in fact, lumbar ROM appears to
have little correlation with work disability status. 39 It is also troubling that replicating the motion,
and spine loads, that occur during the use of many low back extensor machines used for training and
therapy, produces disc herniations when applied to spines in our laboratory! It is clear that some
current “clinical wisdom” needs to be re-examined in the light of relatively recent scientific evidence
(those interested in the literature evidence should consult my review in the Low Back Disorders Text-
book 35 ). It appears that the safest, and mechanically justifiable approach to enhancing lumbar stability
through exercise entails a philosophical approach consistent with endurance — not strength; that
ensures a neutral spine posture when under load; and that encourages abdominal cocontraction and
bracing in a functional way. (A “neutral posture” is defined as one where the joints and surrounding
passive tissues are in elastic equilibrium and thus at an angle of minimal joint load). It is also acknow-
ledged that optimal athletic performance, which demands reaction and prehension challenges, is not
synonymous with health objectives and that additional risk is accepted for extreme ranges of motion
and particular motor patterns. The most recent insights provided by Cholewicki suggest that while
steady-state motor patterns are important for daily activity, the health of reflexive motor patterns is
critical for maintaining stability during sudden events 14 — achieving a fit and effective motor control
system probably requires training in a variety of static and dynamic, expected and unexpected, stable
and labile, conditions.
While many muscles have been regarded as primary spine stabilizers, confirmation of their role
requires two levels of analysis. First, engineering — stability analysis must be conducted on anatomically