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PubMed2005

Short rest periods after static lumbar flexion are a risk factor for cumulative low back disorder.

The objective of this work was to study the effect of rest periods of various durations applied between six 10-min sessions of static flexion on the development of cumulative low back disorder (CLBD). Three experimental groups of a feline model were used, and the rest duration between sequential static load periods was set to 5, 10, and 20 min, with a corresponding load-to-rest ratio of 2:1, 1:1 and 1:2, respectively. The reflex electromyographic (EMG) activity from the multifidus muscles and supraspinous ligament displacement (creep) were recorded during the flexion periods and over 7 h of rest following the load-rest cycles. It was found that a minor disorder developed in all the groups whereas a severe neuromuscular disorder including a delayed hyperexcitability was observed only in the group subjected to 5 min rest. The two-way ANOVA showed a significant effect of time post loading (p<0.001) and rest duration (p<0.001) on the Normalized Integrated EMG (NIEMG) recovery data; a significant effect of time post loading on the Displacement data (p<0.001) was observed as well. The post hoc Fisher test performed on the NIEMG data during the recovery phase showed a significant difference between the group subjected to 5 min rest and the other two groups (p<0.001). These results suggest that while a short rest period of 2:1 load-to-rest ratio leads to CLBD, longer rest at 1:1 and 1:2 load-to-rest ratio are more favorable for preventing or attenuating the development of CLBD. Short rest periods between sessions of static lumbar flexion, therefore, are a risk factor for the development of CLBD.

Animals↗
PubMed2005

Statistical modelling of fatigue-related electromyographic median frequency characteristics of back and hip muscles during a standardized isometric back extension test.

The purpose of the present study was to evaluate which statistical model - linear, logarithmic, quadratic or exponential - best described the fatigue-related electromyographic (EMG) changes of back and hip muscles. Twenty healthy volunteers performed a modified Biering-Sorensen test. The EMG activity of the latissimus dorsi (LD), longissimus thoracis pars thoracis (LTT) and lumborum (LTL), iliocostalis lumborum pars thoracis (ILT) and lumborum (ILL), multifidus (MF), gluteus maximus (GM) and biceps femoris (BF) was measured bilaterally using surface electrodes. Higher R(2) values were found for the quadratic models (p<0.05 for all muscles), and lower R(2) values for the logarithmic models (p<0.05 for LTT, LTL, ILL, MF and GM). The exponential models generated higher R(2) values compared to the linear ones for the LTT, LTL and MF (all p<0.05). Further analyses revealed, however, that these models did not add useful additional information, and therefore would only increase the complexity. The findings of the current study validate the use of simple linear regression techniques when studying fatigue-related EMG median frequency characteristics of back and hip muscles during isometric contractions.

Adult↗
PubMed2006

Trunk muscle activation patterns during walking at different speeds.

Investigations of trunk muscle activation during gait are rare in the literature. As yet, the small body of literature on trunk muscle activation during gait does not include any systematic study on the influence of walking speed. Therefore, the aim of this study was to analyze trunk muscle activation patterns at different walking speeds. Fifteen healthy men were investigated during walking on a treadmill at speeds of 2, 3, 4, 5 and 6 km/h. Five trunk muscles were investigated using surface EMG (SEMG). Data were time normalized according to stride time and grand averaged SEMG curves were calculated. From these data stride characteristics were extracted: mean SEMG amplitude, minimum SEMG level and the variation coefficient (VC) over the stride period. With increasing walking speed, muscle activation patterns remained similar in terms of phase dependent activation during stride, but mean amplitudes increased generally. Phasic activation, indicated by VC, increased also, but remained almost unchanged for the back muscles (lumbar multifidus and erector spinae) between 4 and 6 km/h. During stride, minimum amplitude reached a minimum at 4 km/h for the back muscles, but for internal oblique muscle it decreased continuously from 2 to 6 km/h. Cumulative sidewise activation of all investigated muscles reached maximum amplitudes during the contralateral heel strike and propulsion phases. The observed changes argue for a speed dependent modulation of activation of trunk muscles within the investigated range of walking speeds prior to strictly maintaining certain activation characteristics for all walking speeds.

Abdominal Muscles↗
PubMedDate not supplied

Neuromechanical characterization of in vivo lumbar spinal manipulation. Part II. Neurophysiological response.

OBJECTIVE: To simultaneously quantify vertebral motions and neuromuscular and spinal nerve root responses to mechanical force, manually assisted, short-lever spinal manipulative thrusts. METHODS: Four patients underwent lumbar laminarthrectomy to decompress the central spinal canal and neuroforamina, as clinically indicated. Prior to decompression, finely threaded, 1.8-mm diameter intraosseous pins were rigidly fixed to the lumbar spinous process (L1 or L3) using fluoroscopic guidance, and a high-frequency, low-noise, 10-g, triaxial accelerometer was mounted to the pin. Following decompression, 4 needle electromyographic (nEMG) electrodes were inserted into the multifidus musculature adjacent to the pin mount bilaterally, and 2 bipolar platinum electrodes were cradled around the left and right S1 spinal nerve roots. With the spine exposed, spinal manipulative thrusts were delivered internally to the lumbosacral spinous processes and facet joints and externally by contacting the skin overlying the respective spinal landmarks using 2 force settings ( approximately 30 N, < 5 milliseconds (ms); approximately 150 N, < 5 ms) and 2 force vectors (posteroanterior and superior; posteroanterior and inferior). RESULTS: Spinal manipulative thrusts resulted in positive electromyographic (EMG) and compound action potential (CAP) responses that were typically characterized by a single voltage potential change lasting several milliseconds in duration. However, multiple EMG and CAP discharges were observed in numerous cases. The temporal relationship between the initiation of the mechanical thrust and the neurophysiologic response to internal and external spinal manipulative therapy (SMT) thrusts ranged from 2.4 to 18.1 ms and 2.4 to 28.6 ms for EMG and CAP responses, respectively. Neurophysiologic responses varied substantially between patients. CONCLUSIONS: Vertebral motions and resulting spinal nerve root and neuromuscular reflex responses appear to be temporally related to the applied force during SMT. These findings suggest that intersegmental motions produced by spinal manipulation may play a prominent role in eliciting physiologic responses.

Aged↗
PubMed2004

Paraspinal muscles and intervertebral dysfunction: part two.

BACKGROUND: One of the diagnostic characteristics of the manipulable spinal lesion--a musculoskeletal disturbance that is claimed to be detected with manual palpation and corrected with manipulation--is said to be altered segmental tissue texture. Little evidence for the nature of abnormal paraspinal tissue texture exists, but indirect evidence from experimental studies supports the plausibility of the concept of protective muscle spasm, although investigations of increased paraspinal electromyography (EMG) associated with low back pain suggests complex changes in motor control rather than simple protective reflexes. OBJECTIVES: To review the literature for evidence that may support or refute proposed explanations for clinically observed altered paraspinal tissue texture associated with the manipulable spinal lesion. This review aims to highlight areas that require further research and make recommendations for future studies. Data Source MEDLINE and CINAHL databases were searched using various combinations of the keywords paraspinal, muscle, palpation, EMG, spine, low back pain, pain, myofascial, hardness, manipulation, reliability, and somatic dysfunction, along with searching the bibliographies of selected articles and textbooks. Data Extraction All relevant data were used. RESULTS: Decreased paraspinal muscle activity and strength associated with low back pain is well established, and there is evidence of changes in muscle fiber composition and localized selective multifidus atrophy. Disturbances in microcirculation have been implicated in nonparaspinal muscle pain. The effect of spinal manipulation on paraspinal EMG activity is inconclusive but promising. CONCLUSION: Little direct evidence exists to support the existence or nature of paraspinal tissue texture change that is claimed to be detected with palpation. The proposal of segmental reflex paraspinal muscle contraction was not supported, at least in association with low back pain. There appears to be a complex relationship between deep paraspinal muscle inhibition during dynamic activity and nonvoluntary guarding behavior during static activity. The relationship between these findings and palpable tissue change is speculative, but increased activity, decreased activity, or both may be responsible for paraspinal tissues detected as abnormal with palpation. Recommendations are outlined for future research.

Atrophy↗
PubMed2006

Paraspinal muscle spindle responses to the duration of a spinal manipulation under force control.

OBJECTIVE: More than 90% of chiropractic patients receive high-velocity, low-amplitude spinal manipulation (HVLA-SM) as part of their chiropractic care. The purpose of the current study was determine how the duration of a lumbar HVLA-SM given under force control affects the discharge of paraspinal muscle spindle afferents. METHODS: Experiments were performed on deeply anesthetized adult cats treated in accordance with the Guiding Principles in the Care and Use of Animals approved by the American Physiological Society. Muscle spindle afferents were identified in the dorsal roots. Neural activity was recorded from individual spindles located in the low back predominately from multifidus and longissimus muscles. Spinal manipulative loads were applied to the L6 vertebra. Force-time profiles were half-sine waves with impulse durations of 25, 50, 100, 200, 400, and 800 milliseconds, delivered at constant magnitudes of 33%, 66%, or 100% body weight. The relationships between spinal manipulation duration and muscle spindle responses were determined using a randomized block design. RESULTS: Mean instantaneous discharge frequency increased with decreasing impulse duration. There appeared to be a threshold effect for impulse duration below which the increase in muscle spindle discharge changed greatly with decreasing impulse duration and above which the discharge did not substantially change with decreasing impulse duration. This threshold was in the vicinity of the duration of an HVLA-SM applied clinically (<or=200 milliseconds). After the manipulation, muscle spindle afferents often became silent, but manipulation duration had little effect on this duration and also had little effect on the time it took for the afferents to recover their initial resting discharge. CONCLUSIONS: The findings suggest that one biomechanical characteristic of an HVLA-SM is its capacity to load paraspinal muscle spindles at a rate where their velocity sensitivity predominates over their length sensitivity.

Animals↗
PubMed2006

Do exercise balls provide a training advantage for trunk extensor exercises? A biomechanical evaluation.

OBJECTIVE: Only a few abdominal muscle exercises have been quantitatively evaluated on both a mat and exercise ball, but the benefits reported for the ball have been equivocally applied to all exercises. The purpose of this study is to evaluate differences in the biological response of muscle activation, lumbar spine posture, and loading variables for extensor exercises performed on 2 surfaces. METHODS: Bilateral muscle activation was recorded from 7 sites (rectus abdominis, external/internal obliques, latissimus dorsi, thoracic/lumbar erector spinae, and multifidus) on 8 subjects. Three-dimensional lumbar spine postures and upper body kinematics were recorded while the participants performed the exercises. An electromyography-driven model was used to calculate spinal loading. RESULTS: Cocontraction of trunk flexor and extensor muscles was reduced by up to 30% for the extension exercises when performed on the ball. Peak muscle activation remained unchanged or decreased, and spinal loading (compression and anterior-posterior shear) decreased when the extension exercises were performed on the ball. The lumbar spine postures attained during the exercises did not differ between surfaces. CONCLUSIONS: The assumption that the use of an exercise ball will always create a greater challenge for the musculoskeletal system was not supported by the findings of this study. Likewise, in a healthy, young population, there does not appear to be any training advantage to performing extensor exercises on a ball versus a mat. However, in a rehabilitation scenario, these exercises performed on a ball could reduce low back loading and hence reduce the potential for reinjury.

Abdominal Muscles↗
PubMed2004

Spinal kinematics and trunk muscle activity in cyclists: a comparison between healthy controls and non-specific chronic low back pain subjects-a pilot investigation.

The aim of this pilot study was to examine whether differences existed in spinal kinematics and trunk muscle activity in cyclists with and without non-specific chronic low back pain (NSCLBP). Cyclists are known to be vulnerable to low back pain (LBP) however, the aetiology of this problem has not been adequately researched. Causative factors are thought to be prolonged forward flexion, flexion-relaxation or overactivation of the erector spinae, mechanical creep and generation of high mechanical loads while being in a flexed and rotated position. Nine asymptomatic cyclists and nine cyclists with NSCLBP with a flexion pattern disorder primarily related to cycling were tested. Spinal kinematics were measured by an electromagnetic tracking system and EMG was recorded bilaterally from selected trunk muscles. Data were collected every five minutes until back pain occurred or general discomfort prevented further cycling. Cyclists in the pain group showed a trend towards increased lower lumbar flexion and rotation with an associated loss of co-contraction of the lower lumbar multifidus. This muscle is known to be a key stabiliser of the lumbar spine. The findings suggest altered motor control and kinematics of the lower lumbar spine are associated with the development of LBP in cyclists.

Adult↗
PubMed2005

Size and shape of the posterior neck muscles measured by ultrasound imaging: normal values in males and females of different ages.

Measurements of muscle strength or size are valuable indicators of muscle status in health and disease. When force cannot be measured directly, due to a particular muscle being one of a functional group or because of pain, size measurements may be the only option. For such data to be useful, normal values for age and gender are necessary. Procedures for scanning and measuring semispinalis capitis and the deep posterior neck muscles (semispinalis cervicis, multifidus and rotatores) using ultrasound imaging are described and normal data provided on size, shape and symmetry of these muscles from a sample of 99 healthy subjects (46 males aged 20-72 years and 53 females aged 18-70 years). Significant gender differences were found (P<0.001) but muscle size did not alter significantly with age. Between-side symmetry can be used to assess abnormality of the deep neck muscle group but not semispinalis capitis. A regression equation is provided for predicting the cross-sectional area (CSA) of the deep neck muscles from spinous process length in males. Clinically, linear measurements can be used to predict the neck muscle CSAs (r=0.66-0.84, P<0.001). The method described for assessing the neck muscles is a potentially valuable tool in clinical practice.

Adaptation, Physiological↗
PubMed2007

Rehabilitative ultrasound measurement of select trunk muscle activation during induced pain.

Rehabilitative ultrasound imaging (RUSI) is considered a valid method to measure muscle activation in key spinal muscles in asymptomatic subjects. Research measuring muscle activation with RUSI in painful subjects is limited. The aim of this study was to determine if changes in muscle activation from experimentally induced pain can be measured by RUSI. Six male subjects performed tasks known to activate the transverse abdominis (TrA) and lumbar multifidus (LM) while RUSI measurements of muscle thickness were obtained during control and hypertonic saline conditions. The abdominal draw-in maneuver was used to volitionally activate the TrA and a series of upper extremity lifting tasks were used to automatically activate the LM. Pain was induced by injecting 5% hypertonic saline into the longissimus muscle adjacent to the LM at the L4 level. The percent change in muscle thickness from rest to contraction represented muscle activation. Activation was significantly less (p<0.01) during the painful condition on 4 of the 5 tasks performed for the LM and on the task performed for the TrA. These results indicate that RUSI can be used to measure pain-related changes in deep trunk muscle activation. Future research should include a larger sample size and women.

Abdominal Muscles↗
PubMed2005

Musculoskeletal support of lumbar spine stability.

Using a biomechanical model and experimental data the self-stabilising behaviour of antagonistic trunk muscles was analyzed. The biomechanical model is constituted of a pair of antagonistic Hill-type muscles, their geometric arrangement with respect to the spine, and the instantaneous centre of rotation in frontal plane. Using Ljapunov's theory, the stability of certain motion and loading situations was analyzed. Applying a sensitivity analysis, the influence of different muscle properties and the geometric arrangement on stability was investigated. The simulations revealed that the stability of spinal movements depended primarily on the geometrical arrangement of muscles and the position of the centre of rotation of the spine, the latter was affected in turn by the activities of the profound muscles. To stabilize the situations simulated oblique muscle arrangements were necessary. In order to define an instantaneous centre of rotation in the lower region of the spine negative attachment angles (medio-lateral decline) of muscles were necessary, corresponding to the real anatomy of obliquus externus muscles. More cranially located instantaneous centres of rotation required positive attachment angles for stability, corresponding to obliquus internus or multifidus muscles. Furthermore, the fibre-type distribution of muscles influenced the stability of the system, i.e. a high percentage of fast-twitch-fibres supported the stabilisation. Conclusions drawn from the simulations were supported by experimental data. Sudden loads and quick-release perturbations with two different amplitudes were applied to the upper body of ten male subjects. In comparison to sudden load situations preactivation of muscles due to an external load, i.e. quick-release perturbation, led to significantly less dependency of the amplitude of deflection on the amplitude of the perturbation. This observation relates to the self-stabilising properties of the musculoskeletal system. In conclusion, training seems to be advantageous if directed towards not only enhancing the endurance capacity of the muscles, but also increasing the cross-sectional area of oblique fast-twitch-fibres. Training should also improve the co-ordination of deep and superficial trunk muscles. These findings may influence physiotherapy and training programs for low back pain patients.

Journal Article↗
PubMed1997

Clinical experience with paraspinal mapping. I: Neurophysiology of the paraspinal muscles in various spinal disorders.

OBJECTIVE: To assess the extent of denervation of the paraspinal muscles in spinal disorders. DESIGN: Nonrandomized prospective trial. SETTING: Electrodiagnostic laboratory of a university spine center and of a private practice in a small community. SUBJECTS: One hundred fourteen consecutive persons referred for electrodiagnosis of spinal or lower extremity disorders. INTERVENTION: The paraspinal mapping (PM) electromyography (EMG) protocol along with codified history, physical examination, extremity EMG, and in 44 cases, radiologic imaging results. MAIN OUTCOME MEASURES: PM scores compared with recently established norms (95% of normal subjects scoring less than < 6), lower extremity (LE) EMG findings, and imaging results. RESULTS: Fifty-eight subjects had normal PM scores; 62 were abnormal. Compared to imaging studies, false positive rate was 8% (1/13). False negative rate (normal PM with definite nerve involvement on imaging) was 33% (6/18), but this decreased to 5% when PM was combined with LE EMG. Four of 4 high lumbar lesions were detected by PM. Of 14 apparent false negatives (13%) compared to LE EMG, 6 had S1 root lesions and 5 had nonspinal lesions. All 7 subjects with isolated S1 radiculopathy had PM scores within normal limits. Occasional polyneuropathies presented with normal PM and abnormal distal findings or with abnormal PM but normal distal findings. No patient with isolated paraspinal findings had evidence of malignancy on follow-up. This report also describes the distribution of denervation in the multifidus, longissimus, and iliocostalis in various disorders. CONCLUSIONS: PM related well to imaging studies and LE EMG. It detects uncommon high lumbar root lesions. S1 may not innervate the paraspinal muscles. There are isolated paraspinal findings in persons without malignancy. The effects of specific muscle denervation on biomechanics, rehabilitation exercise, and prognosis are not known.

Adult↗
PubMed1997

Clinical experience with paraspinal mapping. II: A simplified technique that eliminates three-fourths of needle insertions.

OBJECTIVE: To simplify and minimize the quantified needle examination of the paraspinal muscles (paraspinal mapping [PM]) without compromising sensitivity or specificity. DESIGN: Nonrandomized prospective trial. SETTING: Electrodiagnostic laboratory of a university spine center and of a private practice in a small community. SUBJECTS: One hundred fourteen consecutive persons referred for electrodiagnosis of spinal or lower extremity disorders who had PM data and 35 previously reported asymptomatic volunteers. INTERVENTION: Abbreviated PM protocols were simulated by progressively eliminating data from the 45 needle insertions of the original PM. Simulations involving 35, 15, 13, and 5 insertions resulted in different normal values (95% of asymptomatic volunteers) and different scores in patients. The resulting reclassification of patients as normal or abnormal was compared with the original protocol and with clinical data. MAIN OUTCOME MEASURES: False positive and false negative rates of the simulations compared with the original protocol. RESULTS: Abbreviated protocols involving 30, 15, 13, and 5 needle insertions had normal cutoff scores of less than 5, less than 4, less than 3, and less than 2, respectively, with 2%, 2%, 4%, and 8% false positive rates and 3%, 8%, 13%, and 21% false negative rates compared with the original. In many cases clinical information correlated better with the abbreviated test results than the original PM. CONCLUSIONS: The third protocol compared well with the original PM, and in a limited number of patients with imaging studies demonstrated 92% sensitivity and 92% specificity. By eliminating the iliocostalis, longissimus, and lowest multifidus needle explorations, 73% fewer needle insertions were used. We recommend that this new technique, now called "miniPM," be used in most clinical settings.

Electromyography↗
PubMed2003

The effects of repetitive motion on lumbar flexion and erector spinae muscle activity in rowers.

OBJECTIVE: The purpose of this study was to investigate changes in lumbar flexion together with the pattern and level of muscle activity of selected erector spinae during a rowing trial.Design. Cross-sectional repeated measures design. BACKGROUND: Low back pain is a common problem in rowers. The amount of lumbar flexion occurring during rowing might influence the possibility of injury. METHODS: Sixteen young adult school rowers participated in the study. Changes in lumbar flexion and muscle activity were recorded across the drive phase, at three stages of an ergometer based rowing trial. Lumbar flexion was calculated by computerised motion analysis of surface markers attached to the spinous processes of L1 and S1. Surface electromyography techniques were used to examine the magnitude of activity from three erector spinae muscles. The median frequency of the electromyographic signal was examined to quantify fatigue in the erector spinae muscles during isometric maximal effort muscle activation prior to and after the rowing trial. RESULTS: Lumbar flexion increased significantly (P<0.05) during the rowing trial, as did the magnitude of electromyographic activity from sites over the lumbar multifidus, iliocostalis lumborum and longissimus thoracis muscles. The median frequency decreased significantly (P<0.05) in each muscle examined. CONCLUSIONS: The findings showed that rowers attain relatively high levels of lumbar flexion during the rowing stroke, and these levels are increased during the course of the rowing trial. Indirect evidence of muscle fatigue in erector spinae muscles was also apparent, and this observation may in part be responsible for the increased levels of lumbar flexion observed. RELEVANCE: Excessive lumbar flexion may influence the potential for injury to spinal structures. An awareness of increased lumbar flexion and muscle fatigue in the erector spinae muscles may be important for injury prevention programs for rowers.

Adolescent↗
PubMed2003

Biomechanics and electromyography of a cumulative lumbar disorder: response to static flexion.

OBJECTIVE: To assess the mechanical and neurological processes active in the development of a cumulative trauma disorder (CTD) associated with repetitive exposure to periods of static lumbar flexion. METHODS: The spine of the feline model was subjected to a series of three 10 min sessions of static lumbar flexion with each session followed by a 10 min rest. A 7 h rest period was implemented after the series of three flexion-rest sessions while monitoring viscoelastic (disks, ligaments, etc.) creep and multifidus EMG. A model was fitted to the experimental data from the flexion-rest period and the 7 h recovery period. RESULTS: The creep developed in each 10 min static flexion period did not fully recovery during the following 10 min rest, resulting in a large cumulative creep at the end of the flexion-rest period. The cumulative creep did not fully recover over the following 7 h rest period. A neuromuscular disorder consisting of reduced muscular activity superimposed by spasms during static flexion periods and hyperexcitability during the 7 h recovery was evident. Comparison of the data to previous tests of continuous static flexion for 20 min reveal that the neuromuscular disorder elicited by the series of three 10 min flexion-rest was substantially attenuated when compared to a single 20 min static flexion although the overall work time was 50% larger. CONCLUSIONS: Frequent rest periods are highly beneficial in attenuating the development of a CTD, yet not able to prevent it, as viscoelastic tissues residual creep accumulates and its recovery is of extremely long duration. RELEVANCE: The data provides direct biomechanical and physiological evidence that explain the development of a CTD due to prolonged exposure to static lumbar flexion as well as confirms the epidemiological data correlating such work conditions with substantial increase in symptoms of low back disorders. The benefit of frequent rest periods in attenuating the risk of such a disorder is validated as an effective intervention.

Animals↗
PubMed1996

Can the computerized physical examination differentiate normal subjects from abnormal subjects with benign mechanical low back pain?

Inconsistencies among physicians in the evaluation of benign low back conditions make standardization desirable. A computerized physical examination device was used to evaluate low back pain patients and compare their results with a normative database obtained from a selection of healthy subjects. A high-resolution motion analysis system tracked the movement of skin markers placed on the midline and pelvis. Surface electromyography electrodes placed above L(5) collected data from multifidus. From the kinematics of skin markers during flexion extension with lifts up to 32 kg, and lateral bending with lifts up to 4.6 kg, the following parameters were estimated: lumbosacral angle and elongation, contribution of each lumbar segment to the lordosis reduction, relative pelvic/spine motion and trunk velocity. First, the average normal value for each estimated parameter was determined using 40 normal subjects. For each subject, the difference between his parameter and the normal was processed by an expert system generating a normality index varying from zero (perfect abnormal) to one (perfect normal). To develop the expert system's rules, a preliminary group of 20 very abnormal subjects were used, such that the normality index separated them from the normals. For validation, a set of 29 WCB sprain patients and another set of 42 discogram positive were selected. Each subject was tested and his computerized normality index calculated without any clinicians' input. The computerized normality index was compared with the clinicians' evaluation which was taken to be the gold standard. The Receiver Operating Characteristic technique was used to quantify the discrepancies. Results show that the expert system can detect clinically abnormal subjects with accuracy (sensitivity 83-91% and specificity >/=90%) while providing quantitative information on workers' functional capacities.

Journal Article↗
PubMed2000

Biexponential recovery model of lumbar viscoelastic laxity and reflexive muscular activity after prolonged cyclic loading.

OBJECTIVES: To determine the rest duration required for full recovery of reflexive muscular activity and laxity/creep induced in the lumbar viscoelastic structures (e.g., ligaments, discs, etc.) after 50 min of cyclic loading, and to develop a model describing such recovery. BACKGROUND: It is well established that steady, cyclic or vibratory loading of the lumbar spine induces laxity/creep in its viscoelastic structures. It was also shown that such viscoelastic creep does not fully recover when subjected to rest equal in duration to the loading period. Rest periods of 24 h, however, were more than sufficient to allow full recovery. The exact period of time allowing full recovery of viscoelastic laxity/creep, and its pattern is not known. It is also not known what is the duration required for full recovery of reflexive muscular activity lost due to the laxity/creep induced in the spine during cyclic loading. METHODS: The lumbar spine of 'in vivo' feline preparations was subjected to 50 min of 0.25 Hz cyclic loading applied v ia the L4/5 supraspinal ligament. At the end of the loading period the spine was subjected to prolonged rest, interrupted by a single cycle loading applied hourly for measurement purposes until the laxity was fully recovered (>90%). Reflexive EMG activity was recorded with wire electrodes from the L-1-L-7 multifidus muscles. A biexponential model was fitted to the load and EMG recorded in the recovery period in order to represent viscous and elastic components of structures with different architecture (e.g., disc vs. ligament). RESULTS: Full recovery of the laxity induced by 50 min of cyclic loading at 0.25 Hz required 7 h and was successfully fitted with a biexponential model. Similarly, EMG activity was fully recovered in 4 hours, and often exceeded its initial value during the following 3 h. CONCLUSIONS: Full recovery of laxity induced in the lumbar viscoelastic structures by a given period of cyclic loading requires rest periods, which are several folds longer than the loading duration. Similarly, reflexive muscular activity requires 4 h of rest in order to be restored. Meanwhile, significant laxity can be present in the joints, exposing the spine to potential injury and low back pain. Increased EMG activity at the end of the recovery period may indicate that pain was possibly induced in the spinal structures, inducing hyperexcitability of the muscles during passive loading. RELEVANCE: Although the data was derived from a feline model, and its extrapolation to the human model is not straightforward, the general pattern of decreasing reflexive muscular activity with cyclic loading is expected in both species. Therefore, workers who subject their spine to periods of cyclic loading may be exposed to prolonged periods of laxity beyond the neutral zone limits, without protection from the muscles and therefore the risk of possible injury and low back pain. Pain and muscle hyperexcitability could also be a factor associated with cyclic loading, being expressed several hours after work was completed.

Animals↗
PubMed1996

The role of the iliolumbar ligament in low back pain.

Low back pain is caused by a variety of etiologies. Some clinicians have postulated that much low back pain is due to trauma to the iliolumbar ligament. The iliolumbar ligament is one of the three pelvic-lumbar ligaments and develops during the 12th week of gestation. The iliolumbar ligament appears to be a major stabilizing component between the vertebral spine and the pelvis. The innervation of the iliolumbar ligament appears similar to the posterior lumbar ligaments. Our hypothesis is: micro-trauma to the iliolumbar ligament is the primary cause of many cases of chronic low back pain because (1) it is the weakest component of the multifidus triangle; (2) there is increased susceptibility to injury due to its angulated attachment; (3) it is a primary inhibitor of excess sacral flexion; (4) it is a highly innervated nociceptive tissue; and (5) it plays an increased role with progressive disc degeneration.

Back Pain↗