The modern conditioning and therapeutic market abounds with a host of ideas,
programs and devices intended to enhance proprioception in athletes and
recovering patients. Clients using these methods are required to stand, sit,
lie and execute many different drills on wobble boards, physio balls, sponge
rollers and a multitude of miscellaneous weird and wonderful objects. Does
all of this help or, if it does help, has it more to do with something other
than the balancing drills? The following scientific article (extracts
provided) addresses this issue at length.
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Proprioceptive Measures warrant Scrutiny
Conventional assessment measures may not reflect correct neurological
pathways.
By Danny M. Pincivero, PhD, and Alan J. Coelho, EdD
<http://www.biomech.com/db_area/archives/2001/0103function.bio.html>
Performance of athletic skills and physical fitness activities requires
normal and adequate function of the knee joint. Such function depends on many
factors including neuromuscular integrity, muscle strength, and flexibility.
Also critical to normal knee function are the sensory signals emanating from
the limb itself. Functioning through various reflex pathways, these sensory
signals provide us with a conscious awareness of the internal and external
environments about the lower limb, which in turn provides an indication of
limb position and movement.
This physiological entity was originally described in 1908 by Sir Charles
Sherrington as "proprioception," and has since been the focus of numerous
investigations.1 Proprioception, which has been classified as a sensory
submodality of touch,2 is hypothesized to be related to knee injury
predisposition, particularly in female athletes, and successful exercise
rehabilitation. Unfortunately, very little scientific evidence has supported
such claims. Furthermore, because the knee joint is a common site of injury
resulting in disability, the need for evidence-based conclusions concerning
the functional role of proprioception in injury occurrence and management is
paramount.
What is Proprioception?
Proprioception is defined as the conscious awareness of limb movement and
position. The term proprioception has also been linked to a number of
subconscious neurological and neuromuscular mechanisms that are vital to
human function and locomotion. Various physiological signals that are
initiated in peripheral muscles give rise to spinal pattern generators
producing smooth rhythmical movements, as well as contributing to the
maintenance of muscle tone. These resulting actions of the central nervous
system (CNS) are largely mediated by spinal level reflexes (stretch reflex,
cross-extensor reflex) and cerebellar preprogrammed impulses for corrective
locomotor maneuvers and the maintenance of posture. As many studies have
operationalized "proprioception" into a consciously mediated mechanism, a
well-known and distinct neurophysiological pathway has been described to
explain such events…….
This pathway of conscious knee joint position and movement awareness is
primarily involved in most
tests of proprioception in many studies, but its functional implication
remains clouded and speculative in these investigations…….
A number of key questions surrounding these methods continue to persist,
without clarification at present. Hogervorst and Brand, in a wide-ranging
review, postulated that position and movement awareness tests do not
differentiate between mechanoreceptors arising from the anterior cruciate
ligament and those of any other structure around the knee. The functional
utility of joint replication tests or movement threshold tests at very slow
velocities also remains in doubt. Although some studies suggest low to
moderate correlations between these methods and various clinical and
functional tests, the consensus in the literature is that there are no
functional causal relationships. Another issue relates to the test-retest
reliability of these methods. An adequate approach necessitates
well-controlled reevaluation procedures and full presentation of reliability
estimates (i.e., intra-class correlation coefficients, standard errors of
measurement, coefficients of variation, and 95% confidence intervals).
Unfortunately, most studies that suggest "good" reliability of incorporated
methodology present very little data to support it. The nature of the
proprioception testing procedures also renders evaluation of their validity
difficult.
If one accepts the general premise that performing such tests at very slow
velocities selectively activates articular mechanoreceptors, then it should
be assumed that our conscious perception of limb movement arises from such an
origin. In fact, it is well known that numerous different afferent receptors
give rise to proprioception and that the relative weighting or distribution
of this input will likely be task specific. As these assumptions start to
come up against issues of functionality or applicability, we are prompted to
revisit the intent of the testing mechanisms, as well as the
neurophysiological pathways under question………
Although it is tempting to suggest that surgical intervention has a positive
restorative effect on proprioception, such a suggestion is highly speculative
as preoperative proprioceptive "deficits," measured through joint motion and
replication tests, are clearly inconclusive. Furthermore, the notion that the
ability to consciously appreciate joint motion and position is mediated by
the ACL is unsubstantiated. Hogervorst and Brand specifically stated that
"Studies of proprioception after a rupture or reconstruction of the ligament
should be interpreted in the broader context of whether mechanoreceptors of
the joint or muscles play the primary role in proprioception." Based on the
known neurophysiological pathways involved in joint position and motion
awareness, assessment techniques should be further refined to better reflect
such pathways.
Exercise Training/Rehabilitation
After knee joint injury and/or surgery, restoring function clearly depends on
tissue healing and the enhancement of muscle strength, endurance, and
flexibility. From a practical perspective, exercises aimed at improving
proprioception in addition to activities that are mediated largely by
proprioception, such as balance and posture, have been well incorporated into
clinical practice. ….. . A rehabilitation program augmented with
perturbation training appeared to reduce the number of episodes of the
affected knee giving way during activity.
This pattern, however, doesn't seem to hold true for joint-angle replication
tests of proprioception. Following a four-week period of rehabilitation in 50
ACL-deficient patients, Carter et al showed no improvements in joint position
sense, despite significant improvements in functional testing and isokinetic
quadriceps strength. In light of the results from these few studies, it
quickly becomes apparent that measures of muscle strength and functional
activities can effectively be improved with the inclusion of exercises aimed
at enhancing neuromuscular control……..
Gender Differences and Functional Relationships
The issue of a proprioceptive gender difference has largely been driven by
relatively larger rates of knee injuries in female athletes than in their
male counterparts. Although experts have hypothesized that proprioceptive
acuity is a potential predisposing factor for this injury rate pattern,
conclusive evidence has not justified this claim. Furthermore, little
research has addressed gender-specific patterns of sensation, afferent neural
transmission, or perception. The force-generating capacity of large muscle
groups such as the quadriceps femoris muscle has been shown to be
significantly higher in males than females when normalized for body mass.
Furthermore, males have also demonstrated a significantly greater rate of
fatigue than females, which may largely be due to males' greater proportion
of type II muscle fibers.
Unfortunately, these experimental findings have been unable to lend insight
into a gender-dependent pattern of joint movement sense. Specific to this
issue, Birmingham et al recently showed that the ability to actively and
passively replicate previously positioned knee joint angles in weight-bearing
and nonweight-bearing conditions did not differ between males and females.
They observed that the range of values representing error in joint
replication (in degrees), ranged across the various conditions from 2.45° to
3.08° in females (n = 39) and 2.35° to 3.19° in males (n = 20).
In a study examining proprioception differences between male (n = 17) and
female (n = 17) athletes, movement detection of the dominant knee was
evaluated at a starting angle of 15° of flexion, while moving into either
flexion or extension at a constant rate of 0.5° /sec.38 Interestingly,
significant gender differences were detected while moving into extension, but
not into flexion. However, the calculated mean difference between males and
females for the statistically significant effect (movement into extension)
was 0.84° , while the nonsignificant difference (moving into flexion) was
0.92° ; a higher mean value. This outcome not only underscores the importance
of interpreting "statistically significant" effects, but questions the
"functional significance" of such testing procedures.
Beynnon et al demonstrated no significant relationships between the ability
to detect passive knee movement at 0.1° /sec, and clinical tests of knee
stability in 20 ACL-deficient patients. Such findings have also been
documented by Carter et al who demonstrated no significant correlation
between joint position sense and functional activity tasks (i.e., hopping and
figure-8 runs), functional activity as measured by a questionnaire, and
measures of isokinetic strength in 50 unilateral ACL-deficient patients. In
a study of 26 ACL-deficient and -reconstructed patients, MacDonald et al
observed no significant relationships between the threshold to perception of
passive motion at 0.5° /sec, time from injury to followup or surgery, KT-1000
arthrometer results, and patient satisfaction.
These results are, however, contrary to those of Barrack et al, who showed a
moderate correlation (r = 0.465) between knee laxity and the threshold to
knee motion in 11 ACL-deficient patients. Borsa et al demonstrated
significant correlation between passive knee movement into extension at 0.5°
/sec, and the single-leg hop test (r = -0.46 to r = -0.56). Although this
result may statistically suggest that individuals with the ability to
perceive knee movement sooner would hop a farther distance, there is little
basic scientific evidence linking the static assessment of proprioception
with a ballistic activity such as hopping.
Furthermore, there does not appear to be a sound physiological rationale to
justify using these extremely slow rates of knee displacement (0.1° to 0.5°
/sec), as the detection of movement at these rates may not truly assess
proprioception as it relates to its functional role. It is compelling to
suggest that joint replication tests may provide a better evaluation of
proprioception. In proposing this, however, researchers must reexamine the
relationship between the neural pathways of interest and those that actually
mediate proprioception.
Conclusions and Future Directions
Proprioception is a complex neurophysiological mechanism driven by input from
specialized receptors in the limbs that provide humans with a perception of
joint position and movement. There has been much speculation on the influence
of factors such as muscle fatigue, joint injury and surgery, and gender on
proprioception. But the scientific literature has yet to arrive at a
consensus regarding some of these factors.
Although many studies have been published to date, many more questions have
been raised than answered as a result of these investigations: What is the
precise role of proprioception, defined as conscious joint awareness, during
activities of daily living or athletic endeavor? Must improvements in
proprioception occur for postinjury or postsurgery rehabilitation to be
successful? Perhaps the most compelling question is, do presently used
methods to assess proprioception accurately depict the neurological pathways
that are known to be vital for coordinated inter-limb dynamics and
neuromuscular control? These questions and others are sure to stimulate new
avenues for proprioception research in the future.
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Dr Mel C Siff
Denver, USA
http://groups.yahoo.com/group/Supertraining/
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