Electromyographic study of postural muscles in various positions and movements

Stepping boundary of external force-controlled perturbations of varying durations: Comparison of experimental data and model simulations

This study investigated the stepping boundary - the force that can be resisted without stepping - for force-controlled perturbations of different durations. Twenty-two healthy young adults (19-37 years old) were instructed to try not to step in response to 86 different force/time combinations of forward waist-pulls. The forces at which 50% of subjects stepped (F₅₀) were identified for each tested perturbation durations. Results showed that F₅₀ decreased hyperbolically when the perturbation's duration increased and converged toward a constant value (about 10%BW) for longer perturbations (over 1500 ms). The effect of perturbation duration was critical for the shortest perturbations (less than 1 s). In parallel, a simple function was proposed to estimate this stepping boundary. Considering the dynamics of a linear inverted pendulum + foot model and simple balance recovery reactions, we could express the maximum pulling force that can be withstood without stepping as a simple function of the perturbation duration. When used with values of the main model parameters determined experimentally, this function replicated adequately the experimental results. This study demonstrates for the first time that perturbation duration has a major influence on the outcomes of compliant perturbations such as force-controlled pulls. The stepping boundary corresponds to a constant perturbation force-duration product and is largely explained by only two parameters: the reaction time and the displacement of the center of pressure within the functional base of support. Future work should investigate pathological populations and additional parameters characterizing the perturbation time-profile such as the time derivative of the perturbation.

[Application progress of surface electromyography and surface electromygraphic biofeedback in low back pain]

Objective

To summarize the application progress of surface electromyography (sEMG) and surface electromygraphic biofeedback (sEMGBF) in low back pain (LBP).

Methods

The related literature about the application of sEMG and sEMGBF in diagnosis and therapy of LBP was summarized and analyzed.

Results

As a auxiliary diagnostic technique, lumbar muscle fatigue, lumbar muscle activity disorder, flexion-relaxation phenomenon, and asymmetry of the paravertebral muscle electromygraphic activity were found in patients with LBP by sEMG. For treatment, sEMG combined with sEMGBF technology to form sEMGBF training. sEMGBF training include sEMGBF training and sEMGBF stretching exercise. sEMGBF training can improve lumbar muscle activity disorder, recover muscle function, and relieve back pain.

Conclusion

sEMG can monitor the electromyographic signal and sEMGBF biofeedback information can relax or strengthen the muscle. It is very meaningful for diagnosis and therapy of LBP.

Surface Electromyographic (SEMG) Biofeedback for Chronic Low Back Pain

Biofeedback is a process in which biological information is measured and fed back to a patient and clinician for the purpose of gaining increased awareness and control over physiological domains. Surface electromyography (SEMG), a measure of muscle activity, allows both a patient and clinician to have direct and immediate access to muscle functioning that is not possible with manual palpation or visual observation. SEMG biofeedback can be used to help “down-train” elevated muscle activity or to “up-train” weak, inhibited, or paretic muscles. This article presents a historical and clinical overview of SEMG and its use in chronic low back pain assessment and biofeedback training.

A Physiological Perspective on Treadmill and Sit-to-Stand Workstations

Active workstations, such as treadmill and sit-to-stand workstations, enable office employees to break prolonged sitting with bouts of light-intensity walking and/or standing. Compared with sitting, walking and/or standing accumulated during the workday using these workstations will increase muscle contractions, which may influence blood flow, energy expenditure, metabolism, musculoskeletal health, and brain function. Physiological responses when using treadmill and sit-to-stand workstations may vary due to differences in muscle contraction type (dynamic vs. static) and may thus affect cardio-metabolic and musculoskeletal health and brain function in different ways.

The effect of prior lumbar surgeries on the flexion relaxation phenomenon and its responsiveness to rehabilitative treatment

BACKGROUND CONTEXT

Abnormal pretreatment flexion-relaxation in chronic disabling occupational lumbar spinal disorder patients has been shown to improve with functional restoration rehabilitation. Little is known about the effects of prior lumbar surgeries on flexion-relaxation and its responsiveness to treatment.

PURPOSE

To quantify the effect of prior lumbar surgeries on the flexion-relaxation phenomenon and its responsiveness to rehabilitative treatment.

STUDY DESIGN/SETTING

A prospective cohort study of chronic disabling occupational lumbar spinal disorder patients, including those with and without prior lumbar spinal surgeries.

PATIENT SAMPLE

A sample of 126 chronic disabling occupational lumbar spinal disorder patients with prior work-related injuries entered an interdisciplinary functional restoration program and agreed to enroll in this study. Fifty-seven patients had undergone surgical decompression or discectomy (n=32) or lumbar fusion (n=25), and the rest had no history of prior injury-related spine surgery (n=69). At post-treatment, 116 patients were reevaluated, including those with prior decompressions or discectomies (n=30), lumbar fusions (n=21), and no surgery (n=65). A comparison group of 30 pain-free control subjects was tested with an identical assessment protocol, and compared with post-rehabilitation outcomes.

OUTCOME MEASURES

Mean surface electromyography (SEMG) at maximum voluntary flexion; subject achievement of flexion-relaxation (SEMG≤3.5 μV); gross lumbar, true lumbar, and pelvic flexion ROM; and a pain visual analog scale self-report during forward bending task. Identical measures were obtained at pretreatment and post-treatment.

METHODS

Patients entered an interdisciplinary functional restoration program, including a quantitatively directed, medically supervised exercise process and a multimodal psychosocial disability management component. The functional restoration program was accompanied by a SEMG-assisted stretching training program, designed to teach relaxation of the lumbar musculature during end-range flexion, thereby improving or normalizing flexion-relaxation and increasing lumbar flexion ROM. At 1 year after discharge from the program, a structured interview was used to obtain socioeconomic outcomes.

RESULTS

At pre-rehabilitation, the no surgery group patients demonstrated significantly better performance than both surgery groups on absolute SEMG at maximum voluntary flexion and on true lumbar flexion ROM. Both surgery groups were less likely to achieve flexion-relaxation than the no surgery patients. The fusion patients had reduced gross lumbar flexion ROM and greater pain during bending compared with the no surgery patients, and reduced true lumbar flexion ROM compared with the discectomy patients. At post-rehabilitation, all groups improved substantially on all measures. When post-rehabilitation measures were compared with the pain-free control group, with gross and true lumbar ROM corrected by 8° per spinal segment fused, there were no differences between any of the patient groups and the pain-free control subjects on spinal ROM and only small differences in SEMG. The three groups had comparable socioeconomic outcomes at 1 year post-treatment in work retention, health-care utilization, new injury, and new surgery.

CONCLUSIONS

Despite the fact that the patients with prior surgery demonstrated greater pretreatment SEMG and ROM deficits, functional restoration treatment, combined with SEMG-assisted stretching training, was successful in improving all these measures by post-treatment. After treatment, both groups demonstrated ROM within anticipated limits, and the majority of patients in all three groups successfully achieved flexion-relaxation. In a chronic disabling occupational lumbar spinal disorder cohort, surgery patients were nearly equal to nonoperated patients in responding to interdisciplinary functional restoration rehabilitation on measures investigated in this study, achieving close to normal performance measures associated with pain-free controls. The responsiveness and final scores shown in this study suggests that flexion-relaxation may be a useful, objective diagnostic tool to measure changes in physical capacity for chronic disabling occupational lumbar spinal disorder patients.

What is the best surface EMG measure of lumbar flexion-relaxation for distinguishing chronic low back pain patients from pain-free controls?

OBJECTIVES

Lumbar flexion-relaxation (FR) is a well-known phenomenon that can reliably be seen in normal subjects but not in most chronic low back pain (CLBP) patients. The purpose of this study was to determine which surface electromyographic (SEMG) measures of FR best distinguish CLBP patients from pain-free control subjects. Standing SEMG and lumbar flexion range of motion (ROM) were also evaluated.

METHODS

A cohort of 218 CLBP patients, who were admitted to a functional restoration program, received a standardized SEMG and ROM assessment during standing trunk flexion and reextension. An asymptomatic control group of 30 nonpatients received an identical assessment. Both groups were compared on 8 separate SEMG and 3 flexion ROM measures.

RESULTS

A receiver operating characteristic curve analysis was used to determine how well each measure distinguished between the CLBP patients and the pain-free control subjects. All SEMG measures of FR performed acceptably. Between 79% and 82% of patients, and 83% and 100% of controls were correctly classified. Standing SEMG performed less well. Gross flexion ROM was the best single classification measure tested, correctly classifying 88% of patients and 83% of controls. A series of discriminant analyses found that certain combinations of SEMG and ROM performed slightly better than gross ROM alone for correctly classifying the 2 subjects groups.

DISCUSSION

Because all SEMG measures of FR performed acceptably, the determination of which SEMG measure of FR is "best" is largely dependent on one's specific purpose. In addition, ROM measures were found to be important components of the FR assessment.

Effects of maximal oxygen uptake test and prolonged cycle ergometer exercise on sway density plot of postural control

This work aims at testing the influence of the maximal oxygen uptake test and prolonged cycle ergometer exercise on sway density plot (SDP) parameters of postural control. Sixteen healthy male subjects were submitted to stabilometric tests with eye open and closed, before and after two different exercises. The maximal oxygen uptake test caused decrease of the mean duration of peaks in SDP, decreasing the stability level, without modify the rates of central and muscular torque controls. Conversely, 60 min exercise increased the mean time interval between two consecutive peaks in SDP, thus decreasing the control rate but not changing the stability level. Visual privation had a greater effect on body sway than these exercises, which were applied to muscles that are not the main actuators in body sway control. Concluding, the changes in postural control are dependent on the intensity and duration of exercise.

The quantified lumbar flexion-relaxation phenomenon is a useful measurement of improvement in a functional restoration program

STUDY DESIGN

A prospective cohort study evaluating the quantitative lumbar flexion-relaxation phenomenon (QLFRP), measured with surface electromyographic (SEMG) signals from the erector spinae during trunk flexion pre- and postrehabilitation, in patients with chronic disabling occupational lumbar disorders (CDOLD).

OBJECTIVES

To assess the responsiveness of the QLFRP in documenting change in functional performance during a functional restoration program for CDOLD patients.

SUMMARY OF BACKGROUND DATA

A recent theoretical construct suggests that QLFRP is responsive to change in lumbar range of motion (ROM) during rehabilitation, with high sensitivity and specificity for abnormal QLFRP predicting ROM.

METHODS

A cohort of normal subjects was tested for QLFRP correlated to inclinometric lumbar ROM measures. The cutoff score was applied to a group of CDOLD patients entering a functional restoration program (N = 135), and to program completers (N = 104). Pain and functional self-report scores were compared with SEMG and ROM measures.

RESULTS

The CDOLD group averaged 23.7 months off work. Surgical treatment was provided prerehabilitation to 51% of patients, with 29% receiving lumbar fusions. From pre- to post-treatment, achievement of QLFRP rose from 31% to 74% of patients, while normal ROM rose from 8% to 63% of patients. Compared to the 16% of patients still demonstrating both abnormal QLFRP and ROM, the other groups showed significantly greater improvement in self-reported pain and function, with the best improvements occurring in patients showing normal ROM and QLFRP. The QLFRP showed high sensitivity, but only modest predictive validity and specificity for predicting ROM postrehabilitation. Improvement in sensitivity and predictive validity occur when surgical cases were excluded from the analysis.

CONCLUSION

A majority of patients in an interdisciplinary functional restoration program failed to demonstrate either the QLFRP or normal ROM on admission to the program. A majority of program completers, however, achieved both normal ROM and QLFRP and another 30% demonstrated either normal QLFRP or normal ROM. Both QLFRP and ROM measures were responsive to relevant self-report scales.

Interaction of viscoelastic tissue compliance with lumbar muscles during passive cyclic flexion-extension

Human and animal models using electromyography (EMG) based methods have hypothesized that viscoelastic tissue properties becomes compromised by prolonged repetitive cyclic trunk flexion-extension which in turn influences muscular activation including the flexion-relaxation phenomenon. Empirical evidence to support this hypothesis, especially the development of viscoelastic tension-relaxation and its associated muscular response in passive cyclic activity in humans, is incomplete. The objective of this study was to examine the response of lumbar muscles to tension-relaxation development of the viscoelastic tissue during prolonged passive cyclic trunk flexion-extension. Activity of the lumbar muscles remained low and steady during the passive exercise session. Tension supplied by the posterior viscoelastic tissues decreased over time without corresponding changes in muscular activity. Active flexion, following the passive flexion session, elicited significant increase in paraspinal muscles EMG together with increase in the median frequency. It was concluded that reduction of tension in the lumbar viscoelastic tissues of humans occurs during cyclic flexion-extension and is compensated by increased activity of the musculature in order to maintain stability. It was also concluded that the ligamento-muscular reflex is inhibited during passive activities but becomes hyperactive following active cyclic flexion, indicating that moment requirements are the controlling variable. It is conceived that prolonged routine exposure to cyclic flexion minimizes the function of the viscoelastic tissues and places increasing demands on the neuromuscular system which over time may lead to a disorder and possible exposure to injury.

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.

Postural muscle activity patterns during standing at rest and on an oscillating floor

Postural muscle activity pattern was examined in the eyes-closed state after adequate adaptation to floor anteroposterior oscillation. Twenty-three subjects were grouped almost evenly according to dominance of anterior or posterior postural muscles in the trunk and thigh during quiet stance. In the posterior-dominant group, this dominance was maintained at every frequency in most subjects. In the anterior-dominant group, this dominance was maintained in most subjects at 0.1 and 0.5 Hz but changed to posterior dominance at 1.0 and 1.5 Hz in about half the subjects. Periodicity of muscle activity was evaluated by EMG amplitude spectrum at the floor oscillation frequency. Periodicity of posterior-dominant muscles in the trunk and thigh increased with increasing oscillatory frequency. In the trunk, the periodicity did not differ significantly between posterior-dominant and anterior-dominant groups. However, in the thigh, periodicity was significantly lower in the anterior-dominant muscles. This was considered to be caused by nonperiodic alternating action of the anterior and posterior muscles. In the lower leg, posterior dominance was observed in quiet stance and at all oscillation frequencies. Periodicity of soleus and gastrocnemius increased at higher frequencies and was higher in gastrocnemius than in soleus. The periodicity difference between both muscles decreased with increasing oscillation frequency.

Repeated spinal flexion modulates the flexion-relaxation phenomenon

OBJECTIVES

To determine if repeated spinal flexion and loading modulate the deactivation of lumbar muscles near full flexion (flexion-relaxation).

DESIGN

Repeated measures experimental study of the effect of repetitive trunk flexion and added mass on the flexion-relaxation phenomenon.

BACKGROUND

Repeated flexion causes muscular fatigue, creep of passive tissues and diminished protective reflexes. However, flexion-relaxation has not been studied in repeated trunk flexion, and could be related to the increased risk of low-back disorders.

METHODS

Thirty healthy young subjects performed 100 trunk flexion movements between standing and full flexion. Erector spinae electromyography and lumbar spine flexion were measured during cycles 1-10 (no load), 11-20 (performed holding a mass in the hands), 81-90 (mass in the hands) and 91-100 (no load). The spinal flexion angle at myoelectric silence and full flexion were extracted from each movement cycle.

RESULTS

Twenty-three of the 30 subjects showed flexion-relaxation throughout the repeated trunk flexion. The flexion-relaxation and maximum flexion angles increased at the end of the experiment; the flexion-relaxation angle relative to the maximum flexion angle also increased. This effect depended on the load condition; the flexion-relaxation and maximum flexion angles showed a greater increase in the unloaded than loaded condition.

CONCLUSIONS

The flexion-relaxation phenomenon was changed due to repeated trunk flexion. The increases in flexion-relaxation angle likely involve changes to the neuromuscular control system.

RELEVANCE

The deactivation of the erector muscles near full flexion occurs at a greater spinal flexion angle and a greater proportion of maximum spinal flexion following repeated spinal flexion. This may be related to the increased risk of injury associated with repeated flexion.

Evidence of altered lumbopelvic muscle recruitment in the presence of sacroiliac joint pain

STUDY DESIGN

Cross-sectional study of electromyographic onsets of trunk and hip muscles in subjects with a clinical diagnosis of sacroiliac joint pain and matched control subjects.

OBJECTIVES

To determine whether muscle activation of the supporting leg was different between control subjects and subjects with sacroiliac joint pain during hip flexion in standing.

BACKGROUND

Activation of the trunk and gluteal muscles stabilize the pelvis for load transference; however, the temporal pattern of muscle activation and the effect of pelvic pain on temporal parameters has not been investigated.

METHODS

Fourteen men with a clinical diagnosis of sacroiliac joint pain and healthy age-matched control subjects were studied. Surface electromyographic activity was recorded from seven trunk and hip muscles of the supporting leg during hip flexion in standing. Onset of muscle activity relative to initiation of the task was compared between groups and between limbs.

RESULTS

The onset of obliquus internus abdominis (OI) and multifidus occurred before initiation of weight transfer in the control subjects. The onset of obliquus internus abdominis, multifidus, and gluteus maximus was delayed on the symptomatic side in subjects with sacroiliac joint pain compared with control subjects, and the onset of biceps femoris electromyographic activity was earlier. In addition, electromyographic onsets were different between the symptomatic and asymptomatic sides in subjects with sacroiliac joint pain.

CONCLUSIONS

The delayed onset of obliquus internus abdominis, multifidus, and gluteus maximus electromyographic activity of the supporting leg during hip flexion, in subjects with sacroiliac joint pain, suggests an alteration in the strategy for lumbopelvic stabilization that may disrupt load transference through the pelvis.

Quantifying the lumbar flexion-relaxation phenomenon: theory, normative data, and clinical applications

STUDY DESIGN

A two-part investigation was conducted: 1) a prospective study of asymptomatic subjects quantitatively comparing trunk mobility to surface electromyographic (sEMG) signals from the erector spinae during trunk flexion; and 2) a prospective repeated-measures cohort study of patients with chronic disabled work-related spinal disorder tested for the flexion-relaxation (FR) phenomenon while measured simultaneously for lumbar spine inclinometric range of motion (ROM).

OBJECTIVES

To describe a theoretical model for the potential use of FR unloaded in assessing patients with chronic low back pain patients before and after rehabilitation, and to establish a normative database (Part 1) for subsequent use in comparison to patients with chronic low back pain (Part 2). The second part of the study assessed the clinical utility of combined sEMG and ROM measurements for assessing the FR phenomenon as a test to assist potentially in planning rehabilitation programs, guiding patients' individual rehabilitation progress, and identifying early posttreatment outcome failures.

SUMMARY OF BACKGROUND DATA

The FR phenomenon has been recognized since 1951, and it can be reproducibly assessed in normal subjects with FR unloaded. It can be found intermittently in patients with chronic low back pain. Recent studies have moved toward deriving formulas to identify FR, but only a few have examined a potential relation between inclinometric lumbar motion measures and the sEMG signal. No previous studies have developed normative data potentially useful for objectively assessing nonoperative treatment progress, effort, or the validity of permanent impairment rating measures.

METHODS

In Part 1, 12 asymptomatic subjects were evaluated in an intra- and interrater repeated-measures protocol to examine reliability of sEMG signal readings in FR, as well as ROM measures at FR and maximum voluntary flexion. The mean sEMG signal averaging right-left electrode recordings, as well as the gross, true, and sacral lumbar ROM measurements, were recorded as normative data. In Part 2, 54 patients with chronic disabled work-related spinal disorder referred as candidates for tertiary functional restoration rehabilitation participated in a standardized assessment protocol for sEMG and ROM measurement before rehabilitation. Those who completed the program were retested with the identical methodology after rehabilitation (n = 34) using the empirically derived cutoff scores for sEMG readings at FR and ROM from Part 1 and prior scientific literature. Pain disability self-reported scores were correlated with sEMG and ROM. Sensitivity and specificity of the sEMG for identifying abnormal motion were assessed.

RESULTS

In Part 1, the ability of the experienced testers to measure ROM and sEMG reliably at FR was high (r >or= 0.92; P < 0.001). All asymptomatic subjects achieved FR at a tightly clustered range of mean sEMG signals from 1 to 2.3 microV. Most of the variation between motion at FR and maximum voluntary flexion occurred through the hip (sacral) motion component of the gross (or total) motion measured at T12. In Part 2, posttreatment reliability for ROM, sEMG, and the ability to detect the FR point was high (r >or= 0.82; P < 0.001). More than 30% of the 54 patients tested before treatment demonstrated ability to achieve FR, with FR usually associated with higher ROM than in the non-FR patients. After treatment, 94% of those who completed the program achieved FR, including all those who achieved FR before treatment. Flexion-relaxation was associated with major improvement in ROM and pain disability self-report.

CONCLUSIONS

Flexion-relaxation measures a point at which true lumbar flexion ROM approaches its maximum in asymptomatic subjects. This also is the point at which lumbar extensor muscle contraction relaxes, allowing the lumbar spine to hang on its posterior ligaments. The gluteal and hamstring muscles then lower the flexed trunk even further by allowing the pelvis to rotate around the hips. This phenomenon was subsequently found in Part 2 to offer a potentially promising method for individualizing rehabilitation treatment, decreasing unnecessary utilization, identifying potential postrehabilitation treatment failures, and assessing permanent impairment rating validity. Moreover, this is the first study to demonstrate systematically that an absence of FR in patients with chronic low back pain can be corrected with treatment.

Diverging intramuscular activity patterns in back and abdominal muscles during trunk rotation

STUDY DESIGN

An intramuscular electromyographic study was performed on trunk rotations during sitting and standing.

OBJECTIVE

The aim was to provide new information on activation levels for deep trunk muscles in various unresisted and resisted trunk rotations.

SUMMARY AND BACKGROUND DATA

Frequent daily trunk twisting and decreased maximal strength during trunk rotation have been associated with low back pain or sciatic pain. However, the involvement of deep trunk muscles during different trunk rotations is relatively unknown.

METHODS

Ten healthy subjects participated. Fine-wire electrodes were inserted, under ultrasound guidance, into psoas, quadratus lumborum, the superficial medial lumbar erector spinae (ES-s, multifidus) and its deep lateral portion (ES-d, iliocostalis), iliacus, rectus abdominis, obliquus externus, and obliquus internus.

RESULTS

The highest involvement for all muscles was observed on the ipsilateral side, in maximal trunk twists with shoulder resistance, except obliquus externus, which showed a dominant contralateral side, and rectus abdominis, which was little activated in all rotations. In contrast, maximal trunk twist without shoulder resistance, i.e., freely performed, resulted generally in lower levels for all muscles involved and in a shift of side dominance for the lumbar muscles quadratus lumborum, psoas, and ES-s.

CONCLUSIONS

During trunk rotations the activity patterns for various trunk muscles could drastically change, and even be the opposite, between the two body sides, within the same type of task, depending on several factors such as initial position, effort level, sitting or standing, and external shoulder resistance.

Analyses of myo-electrical silence of erectors spinae

Electromyographic activity of the erector spinae was studied in 25 healthy, young individuals during forward bending and then coming back to erect posture. Sudden onset of electrical silence called the flexion-relaxation phenomenon was seen to occur in all at 57% of the maximum hip flexion and at 84% of the maximum vertebral flexion. Abrupt re-commencement of the activity was seen at almost similar flexion angle while coming back to erect position. The experiment was repeated with the buttocks held against the wall so as to prevent the posterior migration of the pelvis and also the hip flexion to some extent. The effect was to produce inhibition of the electrical activity earlier at 75% of maximum vertebral flexion (p<0.001) while reactivation of erector spinae occurred soon after the extension started from the maximum trunk flexion. Eleven male subjects repeated the experimental task holding 22 lb weight in front and then on their back tied around the iliac crest. In both the instances the myo-electrical silence was found to occur at greater vertebral flexion. It is concluded that the passive equilibrium between gravity induced tensile torque and the extension torque of stretched posterior vertebral ligaments is responsible for the flexion-relaxation phenomenon than the stretch receptors.

Biomechanical analysis of effects of foot placement with varying chair height on the motion of standing up

Individual experience reveals that posterior foot placement enables one to stand up easily from a chair. However, the way in which foot placement affects this motion has not been investigated in detail. This study was performed to examine the effects of foot placement in the initial stage of the dynamics of standing up from a chair. Subjects wearing light-emitting diode markers and surface electrodes stood up from a chair over force plates, and ground reaction force, joint angle, and muscle activity were measured. The motions required to stand up from chairs 30, 40, or 50 cm in height were analyzed with anterior, vertical, and posterior foot placement. With anterior foot placement, the forward-acceleration components of the ground reaction force were recorded with simultaneous and long-sustained activity of the muscles in order to shift the center of gravity of the body forward even more after lift-off. Our findings indicate that the distance between the center of gravity and the point of application of ground reaction force at lift-off are critical factors in the standing-up motion, and that chairs should be of adequate height as well as having sufficient space under the seat to permit the backward movement of the lower legs.

Interaction between the porcine lumbar intervertebral disc, zygapophysial joints, and paraspinal muscles

STUDY DESIGN

A porcine model was used to study whether muscular activation in the paraspinal muscles caused by nerve stimulation in the anulus fibrosus of a lumbar intervertebral disc could be altered by saline injection into the zygapophysial (facet) joint.

OBJECTIVES

To elucidate possible mechanisms regarding the nerve pathways and interactions between the intervertebral disc, zygapophysial joints, and the paraspinal musculature.

SUMMARY OF BACKGROUND DATA

The physiologic basis for chronic low back pain, including muscular spasm, is uncertain. Although extensive research involving the lumbar motion segments and the surrounding tissues has been performed, the neuromuscular connection has not been sufficiently investigated.

MATERIALS AND METHODS

Twenty-three adolescent pigs were used to measure the electromyographic response in the paraspinal musculature to electrical stimulation of the posterolateral L3-L4 anulus fibrosus, before and after introduction of physiologic saline into the zygapophysial joint. Motor unit action potentials were recorded using three sets of needle electrodes placed into the deepest fascicles of the multifidus, bilateral to the L4 and L5 spinous processes, and into the central longissimus musculature, bilateral to the L4 spinous process.

RESULTS

Stimulation of the nerves within the posterolateral anulus of the disc elicited reactions in the paraspinal muscles, namely the lumbar multifidus and longissimus. Introduction of physiologic saline into the zygapophysial joint resulted in a reduction in the motor unit action potential amplitude. This reduction was manifested as an immediate and constant reduction, a graded reduction, or a delayed reaction, during which the reduction occurred an average of 5 minutes after the saline injection.

CONCLUSIONS

Introduction of physiologic saline into the zygapophysial joint reduced the stimulation pathway from the intervertebral disc to the paraspinal musculature. The zygapophysial joints may therefore have a regulating function, controlling the intricate neuromuscular balance in the lumbar motion segment.

Generation II knee bracing for severe medial compartment osteoarthritis of the knee

OBJECTIVE

To investigate the clinical efficacy of the Generation II (G II) knee brace, a newly developed knee orthosis, on patients experiencing severe medial compartment osteoarthritis (OA) of the knee.

DESIGN

Case series.

SETTING

A national medical and pharmaceutical hospital in Japan.

PATIENTS

Twenty primary OA subjects (excluding those with secondary OA), all older than 55 years of age and experiencing only knee joint problems, were selected according to their ability to walk more than 500 meters independent of support. These patients had arthritis in both knees and no less than one half of normal joint space remaining as revealed by roentgenogram studies. The more severely affected side was selected for bracing.

INTERVENTIONS

For 12 months, each patient wore a G II knee brace on the affected knee on a daily basis, removing it only at night. To evaluate the effects of G II OA brace alone, additional use of new oral drugs or any other treatment was prohibited from 1 month before application of the G II OA brace and throughout the trial period.

MAIN OUTCOME MEASURES

Clinical efficacy was evaluated using the Japan Orthopaedic Association's knee scoring system. X-ray evaluation was performed with patients standing on one leg. A dynamometer was used to evaluate isokinetic quadriceps muscle strength. The center of gravity was measured using an X-Y recording. Clinical evaluation was performed every 2 months thereafter. Final evaluation was at 12 months.

RESULTS

Nineteen of the 20 patients answered that they experienced significant pain relief. Knee pain scores on walking increased from 18.0 to 21.5 and on ascending and descending stairs increased from 12.8 to 15.8. The femorotibial angle decreased in 12 of the patients, and the mean angle decreased from 185.1 degrees before application to 183.7 degrees with the brace on at the final observation period. In addition, isokinetic quadriceps muscle strength increased from an average of 36.8 Nm to 42.8 Nm for all patients. In 17 patients, quadriceps muscle strength increased, while it decreased in 2 and remained the same in 1. Finally, lateral movement of the center of gravity decreased compared with before G II application in all patients.

CONCLUSION

G II bracing is a beneficial treatment for severe medial OA of the knee.

Flexion relaxation of the hamstring muscles during lumbar-pelvic rhythm

OBJECTIVE

This study investigated the simultaneous activity of back muscles and hamstring muscles during sagittal forward body flexion and extension in healthy persons. The study was cross-sectional.

DESIGN

A descriptive study of paraspinal and hamstring muscle activity in normal persons during lumbar-pelvic rhythm.

SETTING

A university hospital.

PARTICIPANTS

Forty healthy volunteers (21 men, 19 women, ages 17 to 48 years), all without back pain or other pain syndromes.

MAIN OUTCOME MEASURES

Surface electromyography (EMG) was used to follow activities in the back and the hamstring muscles. With movement sensors, real lumbar flexion was separated from simultaneous pelvic motion by monitoring the components of motion with a two-inclinometer method continuously from the initial upright posture into full flexion. All signals were sampled during real-time monitoring for off-line analyses.

RESULTS

Back muscle activity ceased (ie, flexion relaxation [FR] occurred) at lumbar flexion with a mean of 79 degrees. Hamstring activity lasted longer and EMG activity ceased in the hamstrings when nearly full lumbar flexion (97%) was reached. After this point total flexion and pelvic flexion continued further, so that the last part of lumbar flexion and the last part of pelvic flexion happened without back muscle activity or hamstring bracing, respectively.

CONCLUSIONS

FR of the back muscles during body flexion has been well established and its clinical significance in low back pain has been confirmed. In this study, it was shown for the first time that the hip extensors (ie, hamstring muscles) relax during forward flexion but with different timing. FR in hamstrings is not dependent on or coupled firmly with back muscle behavior in spinal disorders and the lumbar pelvic rhythm can be locally and only partially disturbed.

EMG activities of the quadratus lumborum and erector spinae muscles during flexion-relaxation and other motor tasks

OBJECTIVE: The aim of this study was to provide new information on the myoelectrical activation of the quadratus lumborum, the deep lateral and the superficial medial lumbar erector spinae, the psoas, and the iliacus muscles in various motor tasks. DESIGN: An intramuscular electromyographic study was performed. BACKGROUND: The contribution of individual deep trunk muscles to the stability of the lumbar spine is relatively unknown in different tasks, including the flexion-relaxation phenomenon. METHODS: Seven healthy subjects participated. Fine-wire electrodes were inserted with a needle guided by ultrasound. RESULTS: The highest activity observed for quadratus lumborum and deep lateral erector spinae occurred in ipsilateral trunk flexion in a side-lying position and for superficial medial erector spinae during bilateral leg lift in a prone position. Quadratus lumborum and deep lateral erector spinae were activated when the flexion-relaxation phenomenon was present for superficial medial erector spinae, i.e. when its activity ceased in the latter part of full forward flexion of the trunk, held relaxed and kyphotic. CONCLUSIONS: In general, the activation of the investigated muscles showed a high degree of task specificity, where activation of a certain muscle was not always predictable from its anatomical arrangement and mechanical advantage.

Variant and invariant characteristics of the sit-to-stand task in healthy elderly adults

The purpose of this study was to identify kinetic, kinematic, and electromyographic (EMG) characteristics during sit-to-stand (STS) in healthy elderly subjects that were affected by changes in movement speed or initial starting position. Eight healthy elderly adults performed the STS movement at natural and fast speeds. Their ankles were placed in either 5 degrees or 18 degrees of dorsiflexion prior to the movement. A motion analysis system, single force plate, and EMG equipment were used to collect data on ankle, knee, and hip movement, vertical ground reaction forces, vertical and horizontal velocity of the head, and EMG activity from selected muscles. The data were further described according to three specific phases of the STS movement. Two-way analyses of variance for repeated measures were used to determine which of the kinematic, kinetic, and timing variables were affected by changing the speed of the movement or the initial ankle position. When asked to stand as fast as possible, muscle onsets and movement phases were shortened. However, when expressed as a percent of total movement time, normalized extensor muscle onsets were found to be earlier during fast movement of the task, whereas the other variables were not different. Changing the initial ankle position affected muscle onsets, duration of movement phases, and joint excursion. We conclude from these data that many of the characteristics of the sit-to-stand movement are speed invariant and therefore the STS movement is for the most part programmed.(ABSTRACT TRUNCATED AT 250 WORDS)

Are "passive" extension exercises really passive?

When rehabilitating patients with back dysfunction, extension exercises that are presumably "passive" for the erector spinae muscles are frequently used. The purpose of this study was to record electromyographic (EMG) activity from back extensor muscles to determine if these muscles are truly inactive during these maneuvers. Surface EMG was recorded bilaterally from lower lumbar muscles in 62 pain-free subjects. The root-mean-square EMG activity, recorded in microV, for the four positions tested was (mean +/- SD): lying prone (1.268 +/- 0.902), extension in lying prone (6.713 +/- 6.976), standing neutral (4.760 +/- 3.282), and extension in standing (3.558 +/- 2.273). One-way ANOVA for repeated measures and Tukey's post hoc test were used to analyze the data. The results indicated that EMG activity was greatest for extension in lying prone (p < .05), equivalent between the two standing positions (p > .05), and least when lying prone (p < .05). The results of this study demonstrated that "passive" extension exercises were not truly passive for lumbar back extensor muscles. From a clinical perspective, if the performance of passive back extension is important, extension in lying prone may not be the exercise of choice and having patients lying prone may be the most beneficial.

Electromyographic activity of the abdominal and low back musculature during the generation of isometric and dynamic axial trunk torque: implications for lumbar mechanics

This study focused on the electromyographic activity of the trunk musculature, given the well-documented link between occupational twisting and the increased incidence of low back pain. Ten men and 15 women volunteered for this study, in which several aspects of muscle activity were examined. The first aspect assessed the myoelectric relationships during isometric exertions. There was great variability in this relationship between muscles and between subjects. Further, the myoelectric activity levels (normalized to maximal electrical activity) obtained from nontwist activities were not maximal despite maximal efforts to generate axial torque (e.g., rectus abdominis, maximum voluntary contraction; 22% external oblique, 52%; internal oblique, 55%; latissimus dorsi, 74%; upper erector spinae [T9], 61%; lower erector spinae [L3], 33%). In the second aspect of the study, muscle activity was examined during dynamic axial twist trials conducted at a velocity of 30 and 60 degrees/s. The latissimus dorsi and external oblique appeared to be strongly involved in the generation of axial torque throughout the twist range and activity in the upper erector spinae displayed a strong link with axial torque and direction of twist, even though they have no mechanical potential to contribute axial torque, suggesting a stabilization role. The third aspect of the study was comprised of the formulation of a model consisting of a three-dimensional pelvis, rib cage, and lumbar vertebrae and driven from kinematic measures of axial twist and muscle electromyograms. The relatively low levels of normalized myoelectric activity during maximal twisting efforts coupled with large levels of agonist-antagonist cocontraction caused the model to severely underpredict measured torques (e.g., 14 Nm predicted for 91 Nm measured). Such dominant coactivity suggests that stabilization of the joints during twisting is far more important to the lumbar spine than production of large levels of axial torque.

Variations in blood supply allocations for quadrupedal and for bipedal posture and locomotion

Hemodynamics and orthodynamics were investigated in quadrupeds (dogs) and in bipeds (humans). The subjects were investigated at rest in supine or lateral posture, in quadrupedal and then in bipedal posture, and during locomotion. Quadrupedalism in humans was with subjects on their hands and knees. Bipedalism in dogs was on hindlimbs with the forelimbs held by a technician. Blood flow in the main arteries of the body (aorta, external and internal carotid, subclavian, and femoral) was measured by sonography. Positional variations between the main bones of the body were determined from X-rays. This study investigated the reallocation of blood supply to different regions of the body when it switches from quadrupedal to bipedal posture and locomotion. Compared with resting posture, the principal findings are 1) cardiac output shows a minimal increase for humans in bipedal stance and a noticeable increase for dogs as well as humans in quadrupedal stance; 2) quadrupedal stance in humans and dogs and bipedal stance in dogs require increased blood supply to the muscles of the neck, back, and limbs, while human bipedal stance requires none of these; 3) cerebral blood flow (internal carotid) in humans did not change as a result of bipedal posture or locomotion, but showed a noticeable drop in quadrupedal posture and an even further drop in quadrupedal locomotion. The conclusion is that erect posture and encephalization produced a noticeable readjustment and reallocation of blood flow among the different regions of the body: This consisted in shifting a large volume of blood supply from the musculature to the human brain.

Paraplegic standing controlled by functional neuromuscular stimulation: Part II--Computer simulation studies

We simulated two types of body motion. First, the body position is assumed to be initially perturbed from the upright position, and all muscles are assumed inactive at the initial position. The control law developed in the preceding paper drives the body segments to the standing position. Arm movements are then applied to the body to investigate how performance is affected by an external disturbance. Simulated body motion indicated that the current output-feedback control law functions well. The body can recover upright posture from a highly flexed position, and the controller can then maintain the body near the vertical during arm movements. The simulation results showed three consistent activation patterns based on energy minimization: 1) no antagonistic muscle pairs are coactivated, 2) strong muscles are recruited before weak ones, and 3) fast muscles are recruited before slow ones. The reason for the second and third observations is that energy liberation rate depends heavily on the relative amount of muscle activation. Since the current control law requires muscles to generate specific joint torques at a prescribed time, strong muscles do not have to be activated as much as weak ones, and recruiting a fast muscle at low activation level consumes less energy than recruiting a slow one at high activation level. Although the output-feedback control law functions well according to our simulation results, the static optimization process would, in practice, take too much computational time to make it practical. Based on the consistent activation patterns found in our simulations, we therefore developed a simpler (suboptimal) activation-distribution scheme that takes much less time and still gives nearly identical performance.

Back muscle function during bipedal walking in chimpanzee and gibbon: implications for the evolution of human locomotion

The evolution of erect posture and locomotion continues to be a major focus of interest among paleoanthropologists and functional morphologists. To date, virtually all of our knowledge about the functional role of the back muscles in the evolution of bipedalism is based on human experimental data. In order to broaden our evolutionary perspective on the vertebral region, we have undertaken an electromyographic (EMG) analysis of three deep back muscles (multifidus, longissimus thoracis, iliocostalis lumborum) in the chimpanzee (Pan troglodytes) and gibbon (Hylobates lar) during bipedal walking. The recruitment patterns of these three muscles seen in the chimpanzee closely parallel those observed in the gibbon. The activity patterns of multifidus and longissimus are more similar to each other than either is to iliocostalis. Iliocostalis recruitment is clearly related to contact by the contralateral limb during bipedal walking in both species. It is suggested that in both the chimpanzee and gibbon, multifidus controls trunk movement primarily in the sagittal plane, iliocostalis responds to and adjusts movement in the frontal plane, while longissimus contributes to both of these functions. In many respects, the activity patterns shared by the chimpanzee and gibbon are quite consistent with recent human experimental data. This suggests a basic similarity in the mechanical constraints placed on the back during bipedalism among these three hominoids. Thus, the acquisition of habitual bipedalism in humans probably involved not so much a major change in back muscle action or function, but rather an improvement in the mechanical advantages and architecture of these muscles.

Relaxation phenomenon in lumbar trunk muscles during lateral bending

This paper reports myoelectric activity measurements in the lumbar trunk muscles when subjects performed tasks involving various degrees of lateral bending. Biomechanical model analyses were made to estimate the tensions in the lumbar trunk muscles required to perform those tasks. The tensions and the activity measurements were compared to see if a muscle relaxation phenomenon occurred. A relaxation phenomenon in the erector spinae muscles was observed to occur in quiet standing in a laterally-bent position of the trunk, qualitatively similar to the flexion-relaxation phenomenon reported by Schultz et al. in 1985(13). However, no relaxation was observed to occur in the lateral oblique abdominal muscles in laterally-bent postures of the trunk.

Motor control of voluntary trunk movements in standing

The pattern of activity in different trunk muscles during voluntary trunk movements was studied in the standing position in man. The electromyographic activity from ventral and dorsal trunk muscles on the left and right sides were recorded together with the movements in the sagittal and frontal planes (Selspot optoelectronic system). Movement direction, amplitude, velocity and initial posture were varied. In all movements there was a basic pattern of alternation between antagonist muscle groups. Fast movements were initiated by a sharp burst of activity, whereas slow flexions and side bendings resulted from a decrease in antigravity muscle activity. Movement amplitude was related to the magnitude of the initiating burst, and also to the time of onset of antagonist muscle activity with a braking effect. The contribution of passive internal forces in the braking of a movement was indicated by the myoelectrical pattern of activity, particularly in slow large side bendings, where ipsilateral activity was present at the end of the movement. Sagittal movements starting at different initial trunk inclinations resulted in shifts in onset time and duration between antagonist muscles. The observed modifications are specific adaptations of the motor program to balance changes in mechanical conditions, such as angular acceleration, moment arm for the gravitational force, and intrinsic forces of active and passive structures surrounding the spine and pelvis. In conclusion, the present results demonstrate that trunk movements are generated and controlled by specific patterns of muscle coordination.

Quantitative studies of the flexion-relaxation phenomenon in the back muscles

In quiet standing positions involving substantial trunk flexion, myoelectric activity in the back muscles diminishes to low levels. Aspects of that "flexion-relaxation" phenomenon were explored through measurements of myoelectric activities in 11 young men during performance of 19 isometric tasks in flexed positions. Biomechanical model analyses were used to predict the internal loads imposed on the lumbar trunk structures during those performances. Flexion-relaxation consistently occurred in quiet flexed standing, but marked increases in myoelectric activity were found on imposition of external loads in flexed positions. Increases in myoelectric activity per unit increase in back muscle contraction force increase were nearly the same as those found in upright postures. Whether or not flexion-relaxation occurs, large trunk flexions load the spine heavily.

Use of EMG in a kinesiological study in industry

The study was conducted in an automobile upholstery plant which manufactures interior trim panels and seat covers. The job was one which required workers to lean repetitively across a 965 mm (38 in) high flat table-like die while securing sheets of material to the die. Two employees in the embossing department volunteered to participate in a comparative evaluation of the accumulation of low back fatigue from working for a full day using a die with a 914 mm (35 in) maximum reach requirement versus that of a die with a 813 mm (32 in) maximum reach requirement. Electromyography (EMG) of the low back muscles was the measure used for the evaluation. EMG recordings from static muscular contractions were made at selected intervals for an 8 h work day while maintaining normal production. Integrated EMG amplitude and power frequency shifts formed the bases for comparison. The integrated EMG amplitude increase over the course of the day was 47% and 100%, respectively, for the two subjects while working with the 813 mm (32 in) die; the respective EMG amplitude increases for the day while working with the 914 mm (36 in) die were 83% and 263%. None of the power frequency shifts exceeded a predetermined minimum level considered necessary to indicate fatigue. As a result of this study, the plant reduced as much as possible the maximum reach required on every die in the embossing department in order to reduce worker fatigue.

Erector spinae muscle responses while standing

In 55 normal adult subjects standing erect, stable EMG responses could be recorded from the lumbar erector spinae muscles in response to unilateral sudden are abduction produced by single electrical stimuli applied to the brachial plexus at Erb's point, or to knee and ankle movement produced by stimuli to the posterior tibial nerve in the popliteal fossa.

Reflex responses of paraspinal muscles to tapping

ERECTOR SPINAE REFLEX STUDIES IN HEALTHY SUBJECTS REVEALED TWO RESPONSES: a 12·0±1·6 ms latency, oligosynaptic response, and a 30 to 50 ms latency response with polysynaptic reflex characteristics. There was a silent period after the first and second responses. The effect of limb position, trunk, neck, postural changes, Jendrassik manoeuvre and vibration on both responses were also evaluated.