Biomedical subjects

Moshe Solomonow

Publications and source records attributed to Moshe Solomonow.

18 recordsLinked to original sources

PubMed2006

Work to rest durations ratios exceeding unity are a risk factor for low back disorder; a feline model.

Low back disorders are prominent among the work force engaged in static anterior flexion during the workday. As a continuing part of a long-term research aimed to identify the biomechanical and physiological processes and corresponding risk factors leading to such cumulative trauma disorder (CTD), we ventured to assess the effect of rest and the work-to-rest duration ratios that may prevent CTD. Three groups of the feline model were subjected to three load/rest paradigms: two 30 min loading periods spaced by 10 min rest in Group I, two 30 min loading period spaced by 30 min rest in Group II and one 60 min loading period for Group III. The cumulative loading duration in the three groups was 60 min. Each of the groups were allowed 7h of rest while monitoring EMG and lumbar viscoelastic tissue creep each hour. The results demonstrate that for two 30 min load periods with a 30 min in between rest, an acute neuromuscular disorder was not present whereas for two 30 min loading with a 10 min rest it was. Similarly, for a 60 min loading with long-term rest, the disorder was present. Post hoc Fisher analysis demonstrated significant differences in the delayed hyperexcitability between the first and second group (P<0.0001) and the third and second (P<0.0001) group. Statistical difference in the displacement data of the three groups was not present. ANOVA showed a significant effect of time post-loading (P<0.0001 and different rest durations (P<0.0001) on the EMG data during the 7h recovery. The new data allow us to conclude that a work-to-rest duration ratio of 1:1 can prevent the development of CTD as long as the work periods are not too long (<60 min). Longer static flexion durations do not respond favorably to rest even if it is of equal or longer duration. It is suggested that appropriate durations of rest may be a viable tool to avert CTD in a certain range whereas long static flexion durations should be avoided at all cost.

Animals↗

PubMed2006

High-repetition cyclic loading is a risk factor for a lumbar disorder.

Epidemiological data suggest that prolonged exposure to cyclic lumbar flexion elicits a chronic neuromuscular disorder and disability in workers. This study provides a physiological and biomechanical assessment of various repetitions of cyclic lumbar flexion sessions as a risk factor for development of an acute neuromuscular disorder. An in vivo feline model was subjected to 10 minutes of cyclic (0.25-HZ) loading, followed by a 10-minute rest period, repeated three times in one experimental group, six times in a second group, and nine times in the third group, followed by rest for 7 hours. Displacement of the lumbar viscoelastic tissue and reflex electromyographic (EMG) activity from the lumbar multifidus muscle were monitored. Creep developed and accumulated during each load/rest period and partially recovered during the subsequent rest. Loading periods were characterized by a decrease in reflex EMG activity with superimposed spasms. In the 7-hour recovery period, initial hyperexcitability was present in all groups, whereas only the six- and nine-repetition groups displayed significant delayed hyperexcitability, indicating the presence of acute inflammation. The mathematical model developed fit the data reasonably well, as the R2 values were generally near 0.90. It was concluded that the resulting delayed muscular hyperexcitability constitutes an acute neuromuscular disorder associated with exposure to many repetitions of cyclic lumbar flexion. The acute disorder can become chronic if not allowed sufficient rest to resolve itself. Workers engaged in cyclic lumbar flexion (e.g., loading/unloading, assembly workers) should avoid long-term exposure in order to prevent the development of a chronic neuromuscular condition known as cumulative trauma disorder.

Animals↗

PubMed2005

Flexion-relaxation response to gravity.

The objective of this report was to study the influence of the orientation of gravitational loading on the behavior of anterior and posterior trunk muscles during anterior trunk flexion-extension. Participants (N=13) performed five (5) cycles of trunk flexion-extension while standing with gravity parallel to the body axis and five (5) cycles while in the supine condition (e.g. sit-ups) with gravity perpendicular to the body axis. Surface electromyographic (EMG) patterns from lumbar paraspinal, rectus abdominis, external oblique, rectus femoris, semimembranosis, and biceps femoris muscles were analyzed during each condition. EMG signals were synchronized with lumbar flexion and trunk inclination angles. Flexion-extension from the standing position resulted in a myoelectric silent period of the lumbar posterior muscles (e.g. flexion-relaxation phenomena (FRP)) as well as the hamstring muscles through deep angles during which activity was observed in abdominal muscles. Flexion-extension during sit-ups, however, resulted in a myoelectric silent period of the abdominal muscles and the quadriceps through deep angles during which the lumbar posterior muscles were active. In this condition, the FRP was not observed in posterior muscles. The new findings demonstrate the profound impact of the orientation of the gravity vector on the FRP, the abdominal muscles reaction to gravitational loads during sit-ups and its relationships with lumbar antagonists and thigh musculature. The new findings suggest that gravitational moments requirements dominate the FRP through the prevailing kinematics, load sharing and reflex activation-inhibition of muscles in various conditions. Lumbar kinematics or fixed sensory motor programs by themselves, however, are not the major contributor to the FRP. The new findings improve our insights into spinal biomechanics as well as understanding and evaluating low back disorders.

Adolescent↗

PubMed2005

The memory properties of cold-worked titanium rods in scoliosis constructs.

STUDY DESIGN: Time series monitoring changes in titanium and stainless steel rod curvature kept at a constant temperature of 37 C as a function of time. OBJECTIVES: To assess the possibility of loss of curvature in titanium rods after scoliosis surgery. SUMMARY OF BACKGROUND DATA: Titanium rods have gained use in scoliosis surgery due to their excellent biocompatibility, while allowing medical personnel to obtain undistorted magnetic resonance imaging scans following surgery. However, the impression of several clinicians has been that when screw pullout and/or loss of sagittal balance occurs, it may be due to the rods losing some of their curvature. METHODS: Five 6-mm rods of differing compositions and lengths (titanium 300 and 100 mm, stainless steel 300 and 100 mm, prebent titanium 85 mm) were bent at room temperature with a 3-point rod bender, then placed in an incubator at 37 C. Digital photographs were taken every 2 weeks and analyzed to extract the radius of curvature of each rod. RESULTS: The Ti rods had a significantly decreasing curvature with time. The prebent Ti and stainless steel rods did not exhibit significant change in curvature. CONCLUSIONS: Titanium rods bent at room temperature and then exposed to body temperature over time tend to exhibit "metal memory"; they gradually revert to their original shape. This may result in loss of sagittal balance and/or proximal screw pullout.

Bone Nails↗

PubMed2005

Neuromuscular response to cyclic loading of the anterior cruciate ligament.

BACKGROUND: Cyclic load applied to various joints during occupational and sports activities is epidemiologically linked to higher risk of neuromuscular disorder development. HYPOTHESIS: Passive cyclic loading of the knee will develop laxity and creep in the anterior cruciate ligament, and these may elicit a neuromuscular disorder in the quadriceps and hamstrings. Women may be more susceptible to the disorder. STUDY DESIGN: Controlled laboratory study. METHODS: Male and female groups were subjected to 10 minutes of passive cyclic loading (0.1 Hz) of the knee at a mild load (150-200 N) and at 35 degrees and 90 degrees flexion. Anterior tibial displacement and electromyogram from the quadriceps and hamstrings were monitored during cyclic loading. Maximal voluntary contraction of knee extension and flexion was assessed before and after cyclic loading. The effect of gender and angle on maximal voluntary contraction and quadriceps/hamstrings electromyogram was tested by a 2-way analysis of variance. Differences between the preload and postload data were tested by a paired t test. RESULTS: At a knee angle of 90 degrees, after cyclic loading, a decrease in maximal voluntary contraction during extension was present in men and women, with an associated decrease in quadriceps electromyogram activity. At 35 degrees, a decrease in maximal voluntary contraction in extension was noted in women and men. Electromyogram spasms were present in the quadriceps and hamstrings during the 10-minute cyclic loading in 51.7% of subjects. Analysis of variance demonstrated that ligament creep was significantly greater in women than in men at both knee angles. CONCLUSIONS: Even a mild cyclic loading of the anterior cruciate ligament, for a relatively short period, can elicit substantial creep, laxity, and a neuromuscular disorder. The disorder is composed of spasms and attenuated muscular function that may together create a condition that exposes the knee to injury. Women seem to be more susceptible than men. CLINICAL RELEVANCE: Cyclic actions performed at high frequencies and high-load magnitudes may lead to the occurrence of increased knee laxity and changes in neuromuscular function that, together with fatigue and changes in proprioception, may increase the risk of injury.

Adult↗

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↗

PubMed2004

Static load repetition is a risk factor in the development of lumbar cumulative musculoskeletal disorder.

STUDY DESIGN: In vivo feline model subjected to variable number of repetitions of a short static lumbar flexion followed by an equally long rest period. OBJECTIVES: The purpose of this study was to determine the influence of the number of repetitions as a risk factor in promoting a cumulative low back disorder in the feline model. SUMMARY OF BACKGROUND DATA: Epidemiologic data point out that the increased number of repetitions of static lumbar loading is a major risk factor in the development of cumulative low back disorder. Biomechanical and physiologic confirmation of the epidemiology is lacking. Recent work demonstrated that repetitive static loading results in accumulation of creep in the lumbar viscoelastic tissues, resulting in a neuromuscular disorder consisting of spasms during loading and hyperexcitability of lumbar muscles during following rest. It was also shown that the load magnitude is a major risk factor. It is hypothesized that increased number of repetitions of static load periods result in increased severity of the resulting neuromuscular disorder. METHODS: Static lumbar flexion of 10 minutes duration followed by 10 minutes rest was repeated three times in one experimental group, six times in the second, and nine times in the third group. In all groups, the creep developing in the lumbar viscoelastic tissues as well as the reflexive EMG from the multifidus were monitored during the flexion/rest periods and throughout a 7-hour recovery period after the repetitions. RESULTS: Creep developed and accumulated during each of the flexion/rest periods in the three experimental protocols, with larger residual creep at the end of the nine repetitions. A residual creep was still present at the end of the 7 hours of recovery allowed in each of the three groups. During the flexion/rest sessions, EMG spasms were present, and the presence of an initial hyperexcitability was detected during the 7 hours of recovery in all the preparations. The presence of a delayed hyperexcitability was revealed only in the group subjected to nine flexion/rest periods, while it was not observed in the groups subjected to three and six flexion/rest repetitions. The statistical analysis (post hoc Fisher test) performed on the normalized integrated EMG and displacement data during the recovery phase showed a significant difference between the nine repetitions group and the other two groups (P < 0.0001). The two-way ANOVA analysis revealed a significant effect of time (P < 0.005) and number of repetitions (P < 0.0001) on all considered parameters. CONCLUSIONS: It was concluded that a cumulative neuromuscular disorder develops because of repetition of static lumbar flexion, and the severity of the disorder provoked is magnified by the number of repetitions. Despite the highly favorable 1:1 work-to-rest ratio and the 7-hour post loading rest period, a full recovery of creep was not obtained in this study.

Animals↗

PubMed2004

Longer static flexion duration elicits a neuromuscular disorder in the lumbar spine.

The objective of this study was to assess the impact of two sequential long, static, anterior lumbar flexions on the development of a neuromuscular disorder and to compare it with previously obtained data from a series of short static flexion periods of the same cumulative time (Sbriccoli P, Solomonow M, Zhou BH, Baratta RV, Lu Y, Zhu MP, and Burger EL, Muscle Nerve 29: 300-308, 2004). Static flexions with loads of 20, 40, and 60 N were applied to the lumbar spine over two 30-min periods with a 10-min rest in between. The reflex EMG activity from the multifidus muscles and supraspinous ligament displacement (creep) was recorded during the flexion periods. Creep and EMG were also monitored over 7 h of rest following the work-rest-work cycle. It was found that the creep that developed in the first 30-min flexion period did not recover completely during the following 10 min of rest, giving rise to a large cumulative creep at the end of the work-rest-work session. Spasms were frequently seen within the EMG during the static flexion. Initial and delayed hyperexcitabilities were observed in all of the preparations at any of the three loads explored during the 7-h rest period. ANOVA revealed a significant effect of time (P < 0.0001) on the postloading data. Larger loads elicited larger magnitudes of the initial and delayed hyperexcitabilities, yet were not statistically different. It was concluded that the 3:1 work-to-rest duration ratio resulted in a neuromuscular disorder, regardless of the load magnitude. The conclusions are reinforced in view of the results from a previous study using 60 min of flexion overall but at 1:1 work-to-rest ratio in which only the highest load elicited a delayed hyperexcitability (Sbriccoli et al., Muscle Nerve 29: 300-308, 2004). An optimal dose-to-duration ratio needs to be established to limit, attenuate, or prevent the adverse effects of static load on the lumbar spine while considering the loading duration as a major risk factor.

Animals↗

PubMed2004

Static load magnitude is a risk factor in the development of cumulative low back disorder.

Occupations requiring frequent periods of static lumbar flexion are known epidemiologically to be risk factors for the development of cumulative low back disorder. The impact of the load magnitude sustained during a series of short static lumbar flexions followed by an equally long rest period on the development of a cumulative low back disorder was addressed in an in vivo feline model. Static loads of 20, 40, and 60 N were applied over 10 min of flexion followed by 10-min rest sessions that were repeated six times (for a total of 2 h) while monitoring lumbar viscoelastic creep (laxity) and reflex electromyographic (EMG) activity from the multifidus muscles. Creep and EMG were also monitored over 7 h of rest following the six flexion-rest sessions. It was found that the creep developed in the 10-min flexion periods did not recover completely during the following 10 min of rest, giving rise to a large cumulative creep at the end of the work-rest session. Muscle activity demonstrated spasms during the static flexion periods as well as initial and delayed hyperexcitability during the 7-h rest period. Loads of 20 and 40 N did not result in delayed hyperexcitability, whereas loads of 60 N resulted in delayed hyperexcitability. Statistical analysis demonstrated that increased load significantly intensified the magnitude of the hyperexcitabilities (P < 0.05). Thus, repeated periods of static lumbar flexion were found to result in a transient neuromuscular disorder with an intensity directly related to the load magnitude, which should be considered a compounding risk factor.

Animals↗

PubMed2004

Flexion-relaxation response to cyclic lumbar flexion.

BACKGROUND: The epidemiology classify cyclic lumbar flexion as a risk factor for the development of cumulative low back disorder. Experimental biomechanical data confirming the epidemiology in humans are lacking. The purpose of this study, therefore, is to investigate the flexion relaxation response to sustained cyclic lumbar flexion in humans. METHODS: Twelve normal college aged males performed deep cyclic lumbar flexion at 0.1 Hz for 9 min while recording lumbar paraspinal electromyogram and kinematic data. FINDINGS: The most important observation of the study was the significant increase in the angular excursion of myoelectric silence during the deep part of the flexion phase. The observed increase in myoelectric silence consisted of earlier cessation of EMG during flexion and delayed activation of trunk extensors during extension. EMG magnitude, during flexion, increased approximately 30% over trials (P < 0.0001), and a smaller (10%), but, significant (P < 0.02) EMG magnitude increase was also observed during the extension phase of the cycle. Spasms, an indication of micro damage to viscoelastic tissues, were sporadic and appeared more frequently later in the session and mostly during the silent period. INTERPRETATIONS: It was concluded that increased myoelectric silence during prolonged cyclic flexion-extension demonstrates an enhanced flexion-relaxation phenomenon which reduces lumbar stability and may be detrimental to low back health. The presence of spasms confirm that sustained cyclic lumbar flexion results in micro damage in the viscoelastic tissues. Overall, a neuromuscular disorder was evoked due to a relatively short period of unloaded cyclic lumbar flexion.

Adaptation, Physiological↗

PubMed2004

Frequency-dependent changes in neuromuscular responses to cyclic lumbar flexion.

Repetitive lifting in the workplace has been identified to be a cause of low back disorders. Epidemiologic data further supports an hypothesis that higher repetition rate (i.e. frequency) is an added risk factor. The objective of this study was to provide experimental data testing the above hypothesis. An in vivo feline model was subjected to 20-min of cyclic lumbar loading at frequencies of 0.1 Hz and 0.5 Hz while monitoring the EMG from the L-3/4-L-5/6 multifidus muscles and the creep at the L-4/5 level. Seven hours of rest were allowed after the cyclic flexion/extension was terminated. During this rest period, a single test cycle was performed every hour to assess recovery of EMG and lumbar creep. The results demonstrate that cyclic lumbar flexion elicits a transient neuromuscular disorder consisting of EMG spasms during the cyclic loading and initial and delayed muscular hyperexcitabilities during the rest period. Cyclic loading at 0.5 Hz resulted in significant (p<0.05) increase in the hyperexcitability magnitude and duration during the recovery period. It was concluded that repetitive lumbar loading at fast rates is indeed a risk factor as it induces larger creep in the lumbar viscoelastic tissues which in turn intensify the resulting neuromuscular disorder.

Animals↗

PubMed2003

Biomechanics and electromyography of a common idiopathic low back disorder.

STUDY DESIGN: In vivo feline preparation groups loaded into lumbar flexion at different magnitudes and an unloaded control group. OBJECTIVE: To demonstrate that a static, constant load flexion of the lumbar spine results in a complex neuromuscular disorder. SUMMARY OF BACKGROUND DATA: Epidemiology suggests that static lumbar flexion is a cause of low back disorders. There is little direct experimental evidence describing the physiologic and biomechanical processes that elicit the disorder. Recent evidence shows that static flexion of the spine under constant displacement results in muscular spasms and a prolonged recovery period. The response of the spine to flexion under constant load of various magnitudes (as opposed to constant displacement) is not known. It was hypothesized that static lumbar flexion under constant load may elicit creep in spinal ligaments, discs, etc., causing microdamage and development of a neuromuscular disorder. METHODS: The lumbar spine of the feline was subjected to 20 minutes of constant load static flexion at physiologic load intensities from light to heavy while creep of lumbar viscoelastic tissues and EMG from the multifidus muscles of L3-L4 to L5-L6 were recorded. Recordings were continued over a 7-hour rest period after the static flexion was terminated. RESULTS: Spasms and decreasing reflexive EMG were evident during the loading period, and a transient surge of EMG activity occurred at the beginning of the rest period. A second surge of EMG activity was seen 3-4 hours later. The four components of the neuromuscular disorder were present regardless of the load magnitude. A model was developed to quantify the disorder. CONCLUSION: A four-component neuromuscular disorder was elicited by a 20-minute constant load static flexion even when very light loads were applied. The disorder was elicited by creep of the viscoelastic tissues, which resulted in spasms and muscular hyperexcitability lasting for >24 hours. Although the disorder was transient, the physiologic and biomechanical principles associated with its development could also explain cumulative trauma disorders.

Animals↗

PubMed2003

Transients of the force and surface mechanomyogram during cat gastrocnemius tetanic stimulation.

The aim of the study was to investigate the time relationship between force and muscle surface displacement, detected as the surface mechanomyogram (MMG) by a laser distance sensor, in the transient phases of a tetanic stimulation. For this purpose the motor nerve of the exposed medial gastrocnemius of four cats was supramaximally stimulated at 30, 40 and 50 Hz for 9 s. Force was detected by a transducer connected at the distal tendon while MMG was measured after pointing the laser beam at the muscle belly. We found that the MMG always anticipated and trailed the force changes during the on- and off-phase of the tetani, respectively. Independently of the stimulation rate, the half-times of the two signals were: on-phase, about 76 ms for force and 33 ms for MMG; off-phase, about 83 ms for force and 132 ms for MMG. There are two main comments to make about these results. First, during the on-phase the shortening of the contractile elements results at first in a muscle geometry change with low output force. After this, when the slack of the elastic-connective tissue has been taken up, the tension is efficiently transmitted to the tendon. Second, the different force and MMG dynamics in the on- and off-phases determine a counter-clockwise hysteresis with more force produced at a given muscle surface displacement during relaxation. To explain the results, the possible specific roles of some components of the muscle mechanical model, muscle mechanical properties and intra-muscular phenomena taking place during contraction have been discussed.

Animals↗

PubMed2003

Neuromuscular dysfunction elicited by cyclic lumbar flexion.

An attempt was made to develop an in vivo model that could explain the neurophysiological and biomechanical processes active in the development of the idiopathic low back disorder common in workers who perform repetitive lifting tasks in industry. Passive cyclic flexion of the feline lumbar spine at 0.1 HZ for 20 min resulted in creep of the supraspinous ligament and other lumbar viscoelastic tissues as well as spasms superimposed on a decreasing electromyogram (EMG) elicited reflexly from the multifidus muscles. Rest for 7 h did not allow full recovery of the viscoelastic creep; the multifidus EMG gradually increased with initial and delayed hyperexcitability. Increasing the peak load of the cyclic flexion resulted in larger creep in the passive tissues and required a longer time for recovery of reflex EMG activity and longer delayed hyperexcitability, but development of spasms and hyperexcitability was unaffected. It is conceivable that damage to the viscoelastic tissues elicits an inflammatory process that in turn triggers a transient neuromuscular disorder. The present findings provide a biomechanical and neurophysiological explanation for a common idiopathic low back disorder as well as for the development of a cumulative trauma disorder often seen in workers engaged in repetitive lumbar flexion.

Animals↗

PubMed2003

Neuromuscular disorder in response to anterior cruciate ligament creep.

OBJECTIVE: To determine the effect of creep developed in the anterior cruciate ligament and other viscoelastic knee structures on the function of the flexor and extensor muscles of males and females. DESIGN: Static load applied to the proximal tibia of young healthy male and female subjects in a laboratory setting with maximal voluntary knee flexion and extension performed before and after the load application. BACKGROUND: Static loads applied to various joints during occupational and sports activities are epidemiologically linked to higher than normal rates of disability reports. The physiological and biomechanical processes active in the development of such a neuromuscular disorder are not known. We hypothesize that creep developed in the anterior cruciate ligament due to prolonged static load will have pronounced impact on the reflexive activation of the associated musculature in a manner that may increase the risk of injury. Females are expected to be exposed to higher risk than males. METHODS: Male and female groups performed maximal voluntary knee flexion and extension before and after applying 200 and 150 N, respectively, to the proximal tibia for a 10 min period. Flexion and extension forces as well as electromyograph from agonist and antagonist muscles were measured at 35 degrees and 90 degrees knee flexion. Data was analyzed through repeated measures of analysis of variance. RESULTS: It was found that in extension, quadriceps electromyographic activity increased significantly after anterior cruciate ligament creep while hamstrings co-activation did not change. There was also a trend towards increased extension force after creep was developed, with significant effect of gender (larger increase in females). Similarly, significant increase in hamstrings electromyographic activity and a trend towards increased force during knee flexion was observed but with no effect of gender. Electromyographic spasms from the flexors and extensors were recorded in 30% of the subjects during the 10 min static loading period at 90 degrees angle and from the flexors only at 35 degrees. Creep in the ligament was marginally greater in females than in males with a significant effect of angle, being greater at 35 degrees than in 90 degrees knee flexion. CONCLUSIONS: The results suggest that ligament creep may develop a neuromuscular disorder consisting of spasms, increased electromyography and force in the agonist muscles without compensation from the antagonist. Static loading of a joint, therefore, may develop a neuromuscular disorder compounded with laxity of the ligaments and subject the individual to increased risk of injury. RELEVANCE: The data provides evidence that prolonged static loads applied to the anterior cruciate ligament and associated viscoelastic structures results in unbalanced muscular activation which puts individuals at increased exposure to injury. Work and sports activities should be scheduled while minimizing periods of static joint loading and emphasizing sufficient rest periods to allow recovery of creep and return to balanced muscular activation and co-activation.

Adaptation, Physiological↗

PubMed2003

Flexion-relaxation response to static lumbar flexion in males and females.

OBJECTIVE: To determine if creep developed in the lumbar viscoelastic tissues during a period of static flexion elicited changes in the muscular responses of the flexion-relaxation phenomenon. BACKGROUND: Static lumbar flexion is a risk factor in workers, yet the physiological biomechanical and histological processes active in the evolution of the consequent low back disorder were not demonstrated experimentally. Controlled animal studies show that static lumbar flexion develops creep in the associated viscoelastic tissues and elicits spasms and modification of muscle function. Such neuromuscular changes are to be investigated in this study while assessing normal human subjects via the flexion-relaxation phenomenon. METHODS: Male and female subject groups performed three bouts of lumbar flexion-extension before and after a 10 min period of static lumbar flexion. The surface electromyographic from the erector spinae muscles as well as flexion angle were recorded. The angle in which electromyographic diminished during flexion and initiated during extension was determined and subjected to ANOVA with repeated measures to determine any significant changes in the flexion-relaxation response. RESULTS: The erector spinae were active through a significantly larger angle during flexion and initiated activity significantly earlier during extension after static flexion. Females demonstrated more pronounced changes than males. EMG amplitude did not change significantly. Spasms were recorded in more than half of the subjects during the static flexion period. CONCLUSIONS: Creep developed during a short static lumbar flexion elicited significant changes in the muscular activity pattern of the flexion-relaxation phenomenon. The muscles seem to compensate for the loss of tension in the lumbar viscoelastic tissues, while spasms suggest that some micro-damage was incurred to the viscoelastic tissues. RELEVANCE: Static lumbar flexion is shown experimentally as an activity that constitutes an occupational risk factor for the development of low back disorder.

Adult↗

PubMed2002

Reflex from the ankle ligaments of the feline.

It was found that two to three articular branches of the tibial nerve innervate the medial ligament of the feline ankle. No innervation was found to the laterial ligament. Supramaximal electrical stimulation of the articular nerves was found to elicit electromyographic (EMG) activity in the intrinsic muscles of the foot. EMG activity was not found in any of the calf muscles which cross the ankle. The average time delay from stimulus to EMG activity was 3.8 ms, indicating that a fast, bisynaptic reflex is active, probably for purposes of preventing or correcting foot eversion to maintain joint stability.

Animals↗

PubMed2002

Sensorimotor control of the spine.

The spinal viscoelastic structures including disk, capsule and ligaments were reviewed with special focus on their sensory motor functions. Afferent capable of monitoring proprioceptive and kinesthetic information are abundant in the disc, capsule and ligament. Electrical stimulation of the lumbar afferents in the discs, capsules and ligaments seem to elicit reflex contraction of the multifidus and also longissimus muscles. The muscular excitation is pronounced in the level of excitation and with weaker radiation 1 to 2 levels above and below. Similarly, mechanical stimulation of the spinal viscoelastic tissues excites the muscles with higher excitation intensity when more than one tissue (ligaments and discs for example) is stimulated. Overall, it seems that spinal structures are well suited to monitor sensory information as well as to control spinal muscles and probably also provide kinesthetic perception to the sensory cortex.

Afferent Pathways↗