 |
 |
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. ------------------------------------- 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. --------------------------------------- Dr Mel C Siff Denver, USA http://groups.yahoo.com/group/Supertraining/