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At least 73 records · Page 4Linked to original sources

PubMed2003

[Spectral analysis of electromyography of low back muscle fatigue induced by simulated driving].

OBJECTIVE: To evaluate the effects of different vibration frequency on the back muscle fatigue during simulated driving. METHODS: Thirty-six subjects performed three simulated driving experiments under three vertical vibration frequencies which were 1.8, 4.0, 6.0 Hz respectively and the driving time was 90 minutes. At the same time the electromyography of low back was recorded. RESULTS: The median frequencies calculated from the power spectrum were decreased exponentially under three vertical vibration frequencies, especially under 4.0 Hz vibration frequency. CONCLUSION: The 4.0 Hz vibration frequency has the most important effect on the back muscle fatigue under simulated driving condition.

Adult↗

PubMed1980

Crosses and uncrossed synaptic actions on motoneurones of back muscles in the cat.

Intracellular recording from motoneurones of back muscles was used to analyze their synaptic input. The sample included motoneurones located in Th13--L2 spinal segments, identified by their antidromic invasion following stimulation of medial, intermediate and lateral branches of the dorsal rami. The motoneurones were monosynaptically excited from lowest threshold ipsilateral afferents and from ipsilateral descending spinal tracts. Polysynaptic EPSPs and/or IPSPs were evoked in them from higher threshold ipsilateral and contralateral afferents and from descending spinal tracts, and recurrent inhibition was evoked from ipsilateral motor axon collaterals. There was no evidence of crossed disynaptic inhibition from group I afferents, or crossed recurrent inhibition of these neurones. Supplementary records from another group of neurones in Th13--L2 segments, unidentified but likely to innervate other back or abdominal muscles, showed monosynaptic and polysynaptic PSPs of the same origin, and in addition disynaptic IPSPs and disynaptic EPSPs from contralateral ventral roots. The crossed IPSPs had features of the crossed recurrent IPSPs, while the crossed EPSPs appeared to be more likely evoked by some afferents passing via the ventral roots. Generally, the input to the investigated neurones showed greatest similarities to the input to motoneurones of neck muscles and differed from that reported for tail motoneurones.

Afferent Pathways↗

PubMed1998

The influence of muscle fiber size and type distribution on electromyographic measures of back muscle fatigability.

STUDY DESIGN: This was a cross-sectional study carried out on a group of 31 healthy, consenting volunteers with no history of low back pain (17 men, 14 women). OBJECTIVES: To evaluate the relationship between electromyographic measures of erector spinae fatigability and the muscle's fiber type characteristics. SUMMARY OF BACKGROUND DATA: Using electromyographic techniques, a pronounced fatigability of the muscles of patients with low back pain has been identified. It has been postulated that this is the result of an unfavorable back muscle fiber type distribution, although an association between electromyographic measures of fatigue and the muscle's fiber type characteristics has never been established. METHODS: Two tests of back extensor fatigability were performed (on separate days), each to the limit of endurance: 1) maintenance of 60% total maximum voluntary contraction of the back extensors, and 2) performance of the Biering-Sørensen test. Pairs of surface electrodes were attached to the skin overlying the belly of the erector spinae, bilaterally, at T10 and L3. The median frequency was computed from the electromyographic power spectrum, and fatigability was given by the slope of the linear regression of median frequency on time (MFgrad; %.s-1). One week later, two percutaneous erector spinae muscle biopsy samples were obtained from the same sites described for electromyography (left side only). Samples were prepared for histochemistry for the identification of muscle fiber types. Fiber sizes (cross-sectional areas) were quantified using computerized image analysis. RESULTS: The mean fiber size at each erector spinae region showed a significant correlation with maximum back extensor strength. In the thoracic region, the relative area of the muscle occupied by Type I fibers (which accounts for the relative size and distribution of the fiber types) showed a significant relationship with MFgrad recorded during each fatigue test. A similar relationship was observed for the lumbar region, but for the Biering-Sørensen test only. CONCLUSIONS: The electromyographic changes recorded in back muscles during fatigue appear to be related to the underlying muscle fiber type area distribution. This confirms the usefulness of electromyography in reflecting such muscle characteristics in a noninvasive manner, when monitoring changes in function consequent to the development of, or rehabilitation from, low back pain.

Adult↗

PubMed1997

Wavelet analysis of electromyography for back muscle fatigue detection during dynamic constant-torque exertions.

The fatigue of the back muscles appears to be strongly implicated as a risk factor for acquisition of low back pain, which is one of the leading ills of our industrial society. Previously, researchers have successfully measured the level of muscular fatigue by using the Fourier transform to analyze the frequency content of the electromyogram (EMG). However, due to the requirement that the EMG signal be stationary, the Fourier transform is suitable only for the analysis of static muscle exertions in which the muscle is held at constant length and tension. Because the majority of industrial work tasks are not static in nature, new methods for quantifying fatigue during dynamic work are needed. The wavelet transform is a novel, although mathematically well developed, technique for analyzing non-stationary signals that has only recently been applied to the study of EMG. Consequently, the main objective of this project is to develop techniques, using the wavelet transform, for the quantification of back muscle fatigue during dynamic repetitive working conditions.

Back Pain↗

PubMed1998

Comparison between adjustable and non-adjustable hang-back muscle recession for concomitant exotropia.

We compared the results of strabismus surgery using adjustable and non-adjustable hang-back muscle recessions in 38 patients having concomitant exotropia. The two groups were matched for age of the patient, type of concomitant exotropia, amount of deviation, and type and amount of muscle surgery. At 6 months follow-up, 18 of the 19 patients (95%) in the adjustable hang-back recession group and 17 of the 19 patients (90%) in the non-adjustable hang-back recession group had ocular alignment within 10 prism diopters (PD) of orthophoria. At the most recent follow-up (mean 3.4 years), 12 of the 13 patients (92%) in adjustable hang-back recession group and 12 of the 14 patients (86%) in non-adjustable hang-back recession group had ocular alignment within 10 PD of orthophoria. There was no statistically significant difference in success rates between the two groups at 6 months postoperatively and at the most recent follow-up. This preliminary study suggests that non-adjustable hang-back muscle recession can be considered for routine concomitant exotropia.

Adolescent↗

PubMed1987

Electrical stimulation of the midbrain central gray facilitates lateral vestibulospinal activation of back muscle EMG in the rat.

Electrical stimulation in the midbrain central gray in urethane-anesthetized female rats increased responses of the deep back muscles lateral longissimus and medial longissimus to stimulation of the lateral vestibular nucleus (LVN). During central gray stimulation, LVN stimuli led to larger muscle responses, recruitment of new motor units, and decreased latency of muscle response. Effective central gray sites are hypothesized to act through axons descending to medullary reticular formation. Results are consistent with participation of these neuronal groups in the activation of lordosis behavior, a vertebral dorsiflexion that requires deep back muscle contraction, but these electromyographic results could also be relevant for other behaviors that require vertebral postural adjustments.

Action Potentials↗

PubMedDate not supplied

Isometric muscle strength and quantitative electromyography of back muscles in wrestlers and tennis players.

The isometric motor performance of the trunk muscles was studied in 10 male wrestlers and 9 male tennis players, all of whom were elite athletes. Isometric flexion, extension, and lateral bending were performed. The motor output, including fatigue, was studied by means of a load cell and using electromyography. The wrestlers were found to have symmetrical strength and were stronger in all measured directions, especially in side bending (flexion, 852 N; extension, 951 N; right and left side bending, 759 N and 744 N, respectively), than the tennis players and normal subjects of any published study. The development of fatigue in the erector spinae muscles, as evaluated by spectral analysis of the myoelectric signal, was not symmetrical and was significant bilaterally at the lumbar level and on the right side at the thoracic level. As expected, the tennis players had asymmetrical isometric strength. They were stronger in left side bending than right side bending (643 N compared with 557 N, P less than 0.01), and stronger in extension than flexion (835 N compared with 638 N, P less than 0.01). The development of fatigue in the erector spinae muscles was significant bilaterally at the lumbar level and on the left side at the thoracic level. The development of fatigue in the tennis players was less than that of the wrestlers except for the left thoracic measurement site. Our conclusions are that tennis players appear to be relatively weak in trunk flexion. The wrestlers displayed a development of fatigue that was asymmetrical and was of nearly the same degree as the tennis players, but on the opposite side.

Adult↗

PubMed1999

Surface EMG of shoulder and back muscles and posture analysis in secretaries typing at visual display units.

OBJECTIVE: A study was carried out to investigate temporal changes of activation of shoulder and back muscles in workers at visual display units by means of surface EMG. Moreover, postural parameters were recorded to distinguish fatigue-related from posture-related changes of the myoelectrical activity. METHODS: Nine healthy female office workers typed texts spoken from tape during three 1-h-long sessions. After the first and again after the second hour there was a break of 15 min. Sixteen-channel surface EMG was bipolarly recorded from the erector spinae, trapezius, deltoid and sternocleidomastoid muscles. Root mean square (RMS) and power spectrum median frequency of the EMG were calculated. Sitting posture was assessed using an eight-channel movement analysis system with ultrasound markers. The position of the seventh cervical spinous process and the left and the right acromion were analysed synchronously with the EMG characteristics using regression analysis. RESULTS: The normalised RMS of the left and right trapezius muscle increased, while the median frequency did not change. The increase of the normalised RMS was significantly lower when the linear influence of posture was excluded. On average, the distance between C7 and the left and right acromion decreased within each working an hour. C7 became lower on average by 5.5 mm within an hour, whereas the acromions became lower by only 1.7 mm (left) and 3.3 mm (right). CONCLUSION: The increase in trapezius muscle activity was partly related to a lifting of the shoulders to compensate a slight slumping of the back. Another part of the EMG activity increase has to be attributed to fatigue, to attention-related activity or to the combination of both. Therefore, training of the back muscles and a varied organisation of work might have a preventive effect with respect to musculoskeletal complaints in VDU workers.

Adult↗

PubMed2002

Stronger back muscles reduce the incidence of vertebral fractures: a prospective 10 year follow-up of postmenopausal women.

The long-term protective effect of stronger back muscles on the spine was determined in 50 healthy white postmenopausal women, aged 58-75 years, 8 years after they had completed a 2 year randomized, controlled trial. Twenty-seven subjects had performed progressive, resistive back-strengthening exercises for 2 years and 23 had served as controls. Bone mineral density, spine radiographs, back extensor strength, biochemical marker values, and level of physical activity were obtained for all subjects at baseline, 2 years, and 10 years. Mean back extensor strength (BES) in the back-exercise (BE) group was 39.4 kg at baseline, 66.8 kg at 2 years (after 2 years of prescribed exercises), and 32.9 kg at 10 years (8 years after cessation of the prescribed exercises). Mean BES in the control (C) group was 36.9 kg at baseline, 49.0 kg at 2 years, and 26.9 kg at 10 years. The difference between the two groups was still statistically significant at 10 year follow-up (p = 0.001). The difference in bone mineral density, which was not significant between the two groups at baseline and 2 year follow-up, was significant at 10 year follow-up (p = 0.0004). The incidence of vertebral compression fracture was 14 fractures in 322 vertebral bodies examined (4.3%) in the C group and 6 fractures in 378 vertebral bodies examined (1.6%) in the BE group (chi-square test, p = 0.0290). The relative risk for compression fracture was 2.7 times greater in the C group than in the BE group. To our knowledge, this is the first study reported in the literature demonstrating the long-term effect of strong back muscles on the reduction of vertebral fractures in estrogen-deficient women.

Aged↗

PubMed2001

Effect of step and ramp static contractions on the median frequency of electromyograms of back muscles in humans.

The purpose of this study was to compare the electromyogram median frequency (MF) values from two contraction modes (ramp vs step) at different force levels of eight back muscles. A group of 20 healthy male subjects stood in a dynamometer with the trunk in a vertical position and performed trunk extension contractions using the displayed L5/S1 extension moment as visual feedback. The electromyogram (EMG) signals from four pairs of back muscles were collected at 4,096 Hz using active surface electrodes during two 7 s static ramp contractions ranging from 0% to 100% of the maximal voluntary contraction (MVC) and two 5 s static step contractions performed at five forces (10%, 20%, 40%, 60% and 80% MVC). The root mean square (RMS) and MF of the EMG signals corresponding to 250 ms windows were computed at each force level for both contraction modes. The RMS from the ramp contractions were significantly higher than from the step contractions in six muscles. The corresponding MF showed a significant (alpha = 0.05) contraction mode x force interaction in four muscles. A significant contraction mode main effect was obtained in four muscles having higher MF during step than during ramp contractions. These differences were more obvious (10-15 Hz) and more frequent at the lower (10%, 20% and 40% MVC) forces. It was suggested that mechanisms not related to motor unit recruitment might influence MF in contraction modes. These unknown mechanisms contaminate any possible relationship between the MF measurements and muscle composition.

Adult↗

PubMed2000

Low back muscle activity in an automobile seat with a lumbar massage system.

This investigation was conducted to determine the effects of a massaging lumbar support system on low back muscle activity. The apparatus included a luxury-level automobile seat, six 10-mm diameter bipolar surface electrodes, an amplifier, an analog-to-digital conversion board, data acquisition software, and a personal computer. Six experimental conditions, each involving a variation of massage time, were considered. The dependent variable was the change in the root mean square variation of the EMG signal. One minute of lumbar massage every 5 min was found to have a beneficial effect on low back muscle activity (as compared to no massage). This may prove to be an extremely important result in the quest to combat low back pain attributable to automobile seating.

Analysis of Variance↗

PubMed2002

Bladder autoaugmentation with rectus muscle backing.

PURPOSE: Bladder autoaugmentation is a procedure which includes detrusoromyotomy or detrusorectomy to release intact urothelium which than prolapses and increases bladder capacity and compliance. The prolapsed urothelium is usually covered with de-epithelialized pedicled colonic or gastric patch. We present our initial experience with bladder autoaugmentation using rectus muscle backing. MATERIALS AND METHODS: Between August 1999 and December 2000 autoaugmentation was performed in 4 girls and 3 boys 4 to 11 years old (median age 8). All patients had neurogenic bladder with small capacity and poor compliance. The technique is performed using an extraperitoneal approach through either an inferior midline longitudinal or transverse incision. The procedure is started with a semi-filled bladder to find the right plane and then continues with an almost empty bladder to avoid severe injury of the prolapsed urothelium. Both rectus muscles are dissected from the anterior and posterior sheaths and sutured to detrusor edges. Urothelium is sutured to the muscle at several places to prevent its retraction and shrinkage. Thus, the bladder is fixed and hangs on rectus muscles, that is the anterior abdominal wall. RESULTS: Followup was 10 to 25 months (median 16). Bladder capacity at 6 months postoperatively increased in all patients, and ranged from 162 to 368 ml. (median 266). All patients had clinical improvement, decreased hydronephrosis, no vesicoureteral reflux and better compliance. CONCLUSIONS: Bladder autoaugmentation with rectus muscle backing is a safe and simple procedure. Rectus muscle is a good alternative to other backing materials.

Child↗

PubMed2004

Simultaneous surface electromyography (SEMG) and 31P-MR spectroscopy measurements of the lumbar back muscle during isometric exercise.

The aim of this study was to demonstrate the feasibility of simultaneous surface electromyography (SEMG) and 31P-MR spectroscopy (31P-MRS) measurements on the back muscle of volunteers during the performance of an isometric exercise. Six volunteers (three male, three female) performed a modified Biering-Sörensen test inside a 1.5 T MR scanner while simultaneously recording SEMG signals. A surface coil was used for 31P-MRS with a CSI sequence. Spectra were collected with a voxel resolution of 40 mm x 40 mm x 100 mm and a temporal resolution of 30 s during periods of rest, sustained muscle contraction and recovery. The duration of muscle contraction was 150 s. SEMG analysis yielded a decrease of the mean SEMG frequency of approximately 20%. The SEMG amplitudes were constant or increased up to approximately 150% during exercise. 31P-MRS showed a maximum decrease of the phosphocreatine (PCr) amplitude down to approximately 32% of its initial value. Simultaneously, a doubling of the inorganic phosphate (Pi) signal was observed. The present study demonstrates that simultaneous SEMG and 31P-MRS measurements of the back muscle are feasible during isometric exercises.

Adult↗

PubMed1993

Use of the surface EMG signal for performance evaluation of back muscles.

For well over a decade my associates and I have been developing an objective, noninvasive technique to evaluate the performance of low-back muscles, with emphasis on being able to distinguish between healthy and dysfunctioned backs. Our approach is based on the well-known fact that the EMG signal undergoes a compression in the frequency domain during a sustained muscle contraction. In particular we track the median frequency of EMG signals detected from six muscles in the lower back during an isometric extension of the trunk. The measurements are taken with the Back Analysis System which consists of a postural restraining device, special electrodes for detecting the EMG signals, a muscle fatigue monitor which calculates the median frequencies, and the appropriate software. We have found that the pattern of fatigue exhibited by the six median frequency curves can be used to distinguish individuals who have low-back pain from those who do not with an accuracy of at least 84%. An even more relevant and timely application of our technique is for quantifying the progression of the performance of low-back muscles during a rehabilitation program. Although more work is required to explore the intricacies of the technique, present results provide a convincing indication that it is reliable and that it is ready to be placed into practice.

Back↗

PubMed1987

Electromyographic evaluation of back muscle fatigue with repeated sustained contractions of different strengths.

The aim of the study was to obtain information on changes in surface electromyograms from the lumbar erector spinae muscles during fatiguing isometric contractions. Four male subjects held different target extension forces to fatique in a prone position under carefully controlled biomechanical conditions. Standard deviations of the distribution of EMG amplitudes (RMS values), autoregressive (AR) time series models of the 15th order and spectral densities were computed. At lower force levels, i.e., at about 50 to 100 Nm or 20-40% of estimated maximum voluntary contraction force (MVC), RMS values significantly decreased over time; at the highest level examined (on average 162 Nm), they increased. Over all force levels, the explained variances of AR models increased and mean power frequencies (MPF) decreased with increasing force. The first and second AR coefficients also exhibited significant changes, depending on both contraction time and strength. The AR time series structure of EMGs during short isometric test contractions at the lowest force level within 30 s after the failure point clearly indicated muscle fatigue and some differences remained in their dependence on the preceding force. The results suggest a concept of 'selective fatigue', and provide a basis for refined electromyographic evaluation of back muscle fatigue. Such an evaluation has to consider the force history preceding the failure point, or serious errors become unavoidable. The increase in RMS values does not constitute a criterion of back muscle fatigue at low force levels. AR time series models are recommended for the description of fatigue-induced electromyographic changes.

Adult↗

PubMed1990

Ascending and descending projections to medullary reticular formation sites which activate deep lumbar back muscles in the rat.

The purpose of this study was to determine ascending and descending afferents to a medullary reticular formation (MRF) site that, when electrically stimulated, evoked EMG activity in lumbar deep back muscles. In anesthetized female rats, the MRF was explored with electrical stimulation, using currents less than 50 microA, while EMG activity was recorded from the ipsilateral lateral longissimus (LL) and medial longissimus (ML). MRF sites that evoked muscle activity were located in the gigantocellular nucleus (Gi). At the effective stimulation site, the retrograde fluorescent tracer, Fluoro-Gold (FG), was deposited via a cannula attached to the stimulating electrode. In matched-pair control experiments, FG was deposited at MRF sites that were ineffective in producing EMG activity in LL and ML, for comparison of afferent projections to effective versus ineffective sites. Labeled cells rostral to FG deposition at effective MRF sites were located in the preoptic area, hypothalamus, limbic forebrain and midbrain, with particularly high numbers in the ipsilateral midbrain central gray, tegmentum, paraventricular nucleus and amygdala. At medullary levels, there was a heavy projection from the contralateral Gi. FG labeled cells were also located in the contralateral parvocellular reticular nucleus, and lateral, medial and spinal vestibular nuclei. Labeled cells with ascending projections were observed in greatest number in the rostral cervical spinal cord, with fewer cells at mid cervical levels and even fewer in the lumbar spinal cord. These labeled cells were located primarily in lamina V, VII, VIII and X. Locations of labeled cells following FG deposition at ineffective MRF sites were similar. However, there was a striking difference in the number of cells retrogradely labeled from the effective MRF sites compared to ineffective MRF sites. Significantly greater numbers of labeled cells were observed in the contralateral MRF, the midbrain, and the cervical spinal cord from the FG deposition at effective stimulation sites. These results suggest that one characteristic of MRF sites that activate epaxial muscles is a larger amount of afferent input, from the midbrain central gray and from contralateral Gi, compared to ineffective MRF sites. Ascending and descending inputs converge at the effective MRF sites, and the larger number of descending projections suggests a more powerful contribution of these afferents to deep lumbar back muscle activation.

Animals↗

PubMed1984

Histochemical fiber composition of lumbar back muscles in the rabbit.

The present study of the back muscles of the rabbit, using enzyme histochemical techniques and stereological methods, was undertaken with the view to gaining a better understanding of the fiber-type make-up of the lumbar musculature of this animal. The muscles considered were the multifidus, sacrospinalis and the intertransversarii between levels L5 and L6. Gross examination reveals that the multifidus and the sacrospinalis form the bulk of the lumbar musculature and that these muscles appear white. Between and deep to these two muscles are the red intertransversarii. Histochemically the multifidus and the sacrospinalis are also similar in their fiber-type composition, mostly types IIA and IIB and the percentage of connective tissue that they contain. The intertransversarii, in contrast, are for all practical purposes composed of only type-I fibers. The intertransversarii contain significantly more connective tissue than the other two muscles. It may be concluded that the bulk of the lumbar musculature of the rabbit is phasic while the intertransversarii, containing only type-I fibers and a high percentage of connective tissue, are postural muscles.

Adenosine Triphosphatases↗

PubMed1996

Reliability of electromyographic power spectral analysis of back muscle endurance in healthy subjects.

OBJECTIVE AND DESIGN: To investigate the reliability (within-day and between-days) of measurements of electromyographic (EMG) power spectral values in measurement of the fatigue rate of the back muscles. METHODS: Twelve healthy male subjects were tested in the unsupported trunk holding position for 60 seconds. Two trials were performed on each of two separate sessions 3 days apart. Surface recording electrodes were placed over the iliocostalis lumborum and multifidus and a branched electrode technique was used to decrease cross-talk. OUTCOME MEASURES: Median frequency (MF) was extracted from the EMG signals by fast Fourier transform. Initial MF and the MF slope over time were computed from linear regression analysis. The reliability of the initial MF and the MF slope of the iliocostalis lumborum and multifidus was examined by Pearson's product moment correlation coefficients (Pearson's r), paired t tests, and a one-way analysis of variance (ANOVA) from which intrasubject coefficients of variation (CVintra) and intraclass correlation coefficients (ICC) were derived. RESULTS: For the initial MF, within-day and between-days reliability of the iliocostalis lumborum and multifidus were good (Pearson's r = .79-.94 nonsignificant paired t test, CVintra = 6.5% to 8.5%, ICC = .79-.93). The MF slope showed moderate variability for the iliocostalis lumborum (Pearson's r = .39-.55, nonsignificant paired t test, CVintra = 33.0% to 48.7%, ICC = .37-.56) while better reliability was found for the multifidus (Pearson's r = .77-.87, nonsignificant paired t test, CVintra = 25.8% to 27.5%, ICC = .78-.82). CONCLUSION: The present study indicated that the trunk holding test with the use of EMG power spectral analysis can be a reliable method to measure the fatigue rate of the back muscles if adequate measures are employed to minimize cross-talk. The better reliability of monitoring the fatigue rate of the multifidus may lead to its future use as a clinical measure.

Adult↗