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PubMed1997

Isokinetic and psychophysical lifting strength, static back muscle endurance, and magnetic resonance imaging of the paraspinal muscles as predictors of low back pain in men.

Magnetic resonance imaging was used to determine the cross-sectional areas and the T2-weighted and proton density-weighted signal intensities of the paraspinal muscles in a group of 128 men, aged 35-63, who had varied histories of occupational and leisure-time physical activities. These measures, and the isokinetic lifting, psychophysical lifting, and static back muscle endurance tests were examined as predictors of low back pain over 12 months of follow-up, in the 43 men who reported no low back pain in the year preceding testing. None of the imaging measures or the muscle function tests was useful as a predictor of future low back pain. Associations with the frequency of low back pain before testing were investigated in the larger group. Smaller total cross-sectional area of the paraspinal muscles and greater signal intensities had weak but significant correlations with more frequent low back pain in the previous year, possibly due to muscle atrophy.

Humans↗
PubMedDate not supplied

A new method of quantitative measurement of abdominal and back muscle strength.

A new method of quantitative measurement with a cybex machine is applied to the trunk muscles. The curves of muscle torque and muscle fatigue are easily obtained in clinical medicine. In normal controls, maximal muscle torque is greater in back muscles than in abdominal muscles, and the definite influence of aging is found in both muscles. Furthermore, the trunk muscles are more easily fatigued by a sustained contraction than by repeated contractions, and abdominal muscles are more easily fatigued than back muscles. The role of the trunk muscles in the mechanism of pain production and prevention is still to be determined.

Abdominal Muscles↗
PubMed1992

A universal model of the lumbar back muscles in the upright position.

A model of the lumbar back muscles was constructed incorporating 49 fascicles of the lumbar erector spinae and multifidus. The attachment sites and sizes of fascicles were based on previous anatomic studies, and the fascicles were modeled on radiographs of nine normal volunteers in the upright position. Calculations revealed that the thoracic fibers of the lumbar erector spinae contribute 50% of the total extensor moment exerted on L4 and L5; multifidus contributes some 20%; and the remainder is exerted by the lumbar fibers of erector spinae. At upper lumbar levels, the thoracic fibers of the lumbar erector spinae contribute between 70% and 86% of the total extensor moment. In the upright posture, the lumbar back muscles exert a net posterior shear force on segments L1 to L4, but exert an anterior shear force on L5. Collectively, all the back muscles exert large compression forces on all segments. A force coefficient of 46 Ncm-2 was determined to apply for the back muscles. These results have a bearing on the appreciation of the effects on the back muscles of surgery and physiotherapy.

Adult↗
PubMed1996

Back muscle injury after posterior lumbar spine surgery. A histologic and enzymatic analysis.

STUDY DESIGN: Back muscle injury after posterior lumbar surgery was studied by muscle histology and serum creatine phosphokinase MM isoenzyme activity. OBJECTIVES: To investigate intraoperative factors influencing the magnitude of back muscle injury after posterior lumbar surgery. SUMMARY OF BACKGROUND DATA: The authors previously have reported iatrogenic back muscle injury in an animal model and in humans. Serious injury of the back muscle has been shown by short-term and long-term follow-up evaluation. METHODS: The retraction pressure was monitored, and the retraction pressure-time products were calculated in 24 patients. Early histologic changes of multifidus muscle, which were taken at completion of surgery, and serum creatine phosphokinase MM isoenzyme activity changes were examined. RESULTS: The magnitude of back muscle injury was significant as the pressure-time product increased. Creatine phosphokinase MM isoenzyme activity increased after surgery and reached a plateau 1 day after surgery, followed by recovery to the normal value 1 week after surgery. Creatine phosphokinase MM isoenzyme activity tended to be high in cases with multilevel exposure and with high pressure-time product. CONCLUSIONS: Back muscle injury occurs in all patients who underwent posterior lumbar surgery, and these injuries are related to the retraction pressure, time, and extent of exposure.

Adult↗
PubMed1994

Back muscle injury after posterior lumbar spine surgery. Part 2: Histologic and histochemical analyses in humans.

STUDY DESIGN: The histologic and histochemical changes in back muscle were studied in virgin surgery patients with lumbar spine disorders and in patients who underwent repeat posterior lumbar surgery. OBJECTIVES: The results were correlated to provide the evidences of histologic changes of back muscle after posterior lumbar surgery. SUMMARY OF BACKGROUND DATA: Back muscles were examined histologically and histochemically after posterior lumbar surgery. No previous study has assessed these changes. METHODS: Back muscles were obtained before and after retraction from 18 virgin surgery cases with lumbar spine disorders. In four patients, the retraction pressure was monitored and the retraction pressure-time products ([P][T]) were calculated. In 21 repeat lumbar surgery cases, muscle samples were obtained before muscle retraction. Samples were evaluated by histologic and histochemical methods. RESULTS: Abnormal findings were slight in virgin surgery cases. Early back muscle injury tended to depend on operation time and [P][T] products. Late back muscle injury in reoperated patients was marked. Various types of neurogenic changes were observed more than 10 months after the first operation. CONCLUSIONS: Histologic damages of back muscle due to previous surgical intervention were long-lasting. To avoid permanent muscle injury, the retraction time and pressure should be shortened or the pressure on the back muscle should be monitored during posterior surgery.

Adult↗
PubMed2003

Asymmetry of premotor time in the back muscles of adolescent idiopathic scoliosis.

STUDY DESIGN: In 38 patients with adolescent idiopathic scoliosis (AIS), the correlation between left and right differences in premotor time (D-PMT) of back muscle and clinical findings were analyzed. OBJECTIVE: To investigate the clinical relevance of back muscle D-PMT in AIS. SUMMARY OF BACKGROUND DATA: There have been numerous studies investigating back muscle asymmetry of AIS by EMG, but to date, no studies have measured D-PMT in back muscles. MATERIALS AND METHODS: D-PMT in the back muscles measured in a similar manner as that in the extremity muscles was assessed in 10 nonscoliotic teenaged girls and 38 AIS patients. The correlation between back muscle D-PMT and four factors (age, Risser sign, Cobb angle, and progression of deformity) was investigated. RESULTS: The D-PMT values of back muscle at all levels in the control group were within +/-5 ms, but those in 20 of the 38 AIS patients were more than 5 ms. D-PMT at the lower-end vertebra level was strongly correlated with progression of deformity, but not with age, Risser sign, and Cobb angle. All five patients with D-PMT of more than 10 ms at the lower-end vertebra level had progressive deformity. CONCLUSIONS: D-PMT in back muscle at the lower end vertebra level in AIS correlated closely to the progression of scoliotic deformity, thus suggesting that this phenomenon is associated with the progression in AIS.

Adolescent↗
PubMed2002

Evaluation of measurement strategies to increase the reliability of EMG indices to assess back muscle fatigue and recovery.

The purpose of this study was to assess different measurement strategies to increase the reliability of different electromyographic (EMG) indices developed for the assessment of back muscle impairments. Forty male volunteers (20 controls and 20 chronic low back pain patients) were assessed on three sessions at least 2 days apart within 2 weeks. Surface EMG signals were recorded from four pairs (bilaterally) of back muscles (multifidus at the L5 level, iliocostalis lumborum at L3, and longissimus at L1 and T10) while the subjects performed, in a static dynamometer, two static trunk extension tasks at 75% of the maximal voluntary contraction separated by a 60 s rest period: (1) a 30 s fatigue task and (2) a 5 s recovery task. Different EMG indices (based on individual muscles or averaged across bilateral homologous muscles or across all muscles) were computed to evaluate muscular fatigue and recovery. Intra-class correlation coefficient (ICC) and standard error of measurement (SEM) in percentage of the grand mean were calculated for each EMG variable. Reliable EMG indices are achieved for both healthy and chronic low back pain subjects when (1) electrodes are positioned on medial back muscles (multifidus at the L5 level and longissimus at L1) and (2) measures are averaged across bilateral muscles and/or across two fatigue tests performed within a session. The most reliable EMG indices were the bilateral average of medial back muscles (ICC range: 0.68-0.91; SEM range: 5-35%) and the average of all back muscles (ICC range: 0.77-0.91; SEM range: 5-30%). The averaging of measures across two fatigue tests is predicted to increase the reliability by about 13%. With regards to EMG indices of fatigue, the identification of the most fatigable muscle also lead to satisfactory results (ICC range: 0.74-0.79; SEM range: 21-26%). The assessment of back muscle impairments through EMG analysis necessitates the use of multiple electrodes to achieve reliable results.

Adult↗
PubMed2002

Electromyographic assessment of back muscle weakness and muscle composition: reliability and validity issues.

OBJECTIVE: To assess the reliability and construct validity of various electromyographic indices developed to assess back muscle weakness and muscle fiber composition. DESIGN: A prospective study with repeated measures performed on 3 days along with comparisons of groups presenting different back strength and/or back muscle fiber composition. SETTING: A biomechanics laboratory within a rehabilitation center. PARTICIPANTS: Forty male volunteers (20 healthy, 20 with chronic low back pain) were assessed on 3 different days to assess reliability and to make group comparisons. Thirteen healthy women were also assessed once to obtain a third group with known lower strength and different back muscle fiber composition. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Surface electromyography was recorded for 4 pairs of homologous back muscles while the subjects performed, on a dynamometer, static trunk extension efforts. Electromyographic parameters were computed to assess muscle weakness and muscle fiber composition. The reliability of the data collected across the 3 sessions and comparisons between groups were determined. RESULTS: Electromyographic parameters generally showed good to excellent reliability, but were insensitive to differences in back muscle strength and did not appear to be related to muscle composition. Some trends were observed in the electromyographic parameters across the force levels, but the large interindividual variability impeded statistical comparisons. CONCLUSIONS: The assessment of muscle weakness and muscle fiber composition through electromyographic analysis does not appear feasible, at least on an individual basis, for the muscles of the back.

Adult↗
PubMedDate not supplied

Flexion-relaxation phenomenon in the back muscles. A comparative study between healthy subjects and patients with chronic low back pain.

At a certain position of trunk flexion, there is a sudden onset of electrical silence in back muscles. This is called "flexion-relaxation (F-R) phenomenon." The goals of this study were (1) to evaluate the relationship between flexion angle and activity of back muscles during flexion movement and (2) to determine what the difference is between healthy subjects and patients with chronic low back pain (CLBP). Twenty-five healthy subjects (13 males and 12 females; average age, 28.3 yr) and 20 patients with CLBP (12 males and 8 females; average age, 34.1 yr) volunteered for this study. The subjects were asked to flex forward maximally from the erect position and to maintain full flexion, followed by returning to the initial upright position. Flexion angle of trunk and hip was measured during the examination. Electromyographic activity of erector spinae was also monitored simultaneously. F-R phenomenon was observed in all healthy subjects before reaching the maximum flexion. Electrical silence continued even after extending the trunk began. In contrast, no patients with CLBP demonstrated F-R phenomenon. A significant difference in muscular activities of erector spinae between the groups was obtained when returning to the erect position from the maximum flexion. Moreover, time lag between trunk and hip movement was much greater in patients than in healthy subjects. This study demonstrated that neuromuscular coordination between trunk and hip could be abnormal in patients with CLBP.

Adult↗
PubMed1992

Reticulospinal and reticuloreticular pathways for activating the lumbar back muscles in the rat.

These experiments tested hypotheses about the logic of reticulospinal and reticuloreticular controls over deep back muscles by examining descending efferent and contralateral projections of the sites within the medullary reticular formation (MRF) that evoke EMG responses in lumbar axial muscles upon electrical stimulation. In the first series of experiments, retrograde tracers were deposited at gigantocellular reticular nucleus (Gi) sites that excited the back muscles and in the contralateral lumbar spinal cord. The medullary reticular formation contralateral to the Gi stimulation/deposition site was examined for the presence of single- and double-labeled cells from these injections. Tracer depositions into Gi produced labeled cells in the contralateral Gi and Parvocellular reticular nucleus (PCRt) whereas the lumbar injections retrogradely labeled cells only in the ventral MRF, indicating that separate populations of medullary reticular cells project to the opposite MRF and the lumbar cord. In the second series of experiments the precise relationships between the location of neurons retrogradely labeled from lumbar spinal cord depositions of the retrograde trace, Fluoro-Gold (FG) and effective stimulation tracks through the MRF were examined. The results indicate that the Gi sites that are most effective for activation of the back muscles are dorsal to the location of retrogradely labeled lumbar reticulospinal cells. To verify that cell bodies and not fibers of passage were stimulated, crystals of the excitatory amino acid agonist, N-methyl-D-aspartate (NMDA) were deposited at effective stimulation sites in the Gi. NMDA decreased the ability of electrical stimulation to activate back muscles at 5 min postdeposition, indicating a local interaction of NMDA with cell bodies at the stimulation site. In the third series of experiments, electrical thresholds for EMG activation along a track through the MRF were compared to cells retrogradely labeled from FG deposited into the cervical spinal cord. In some experiments, Fast Blue was also deposited into the contralateral lumbar cord. Neurons at low threshold points on the electrode track were labeled following cervical depositions, indicating a direct projection to the cervical spinal cord. The lumbar depositions, again, labeled cells in MRF areas that were ventral to the locations of effective stimulation sites, primarily on the opposite side of the medulla. In addition, the lumbar depositions back-filled cells in the same cervical segments to which the Gi neurons project. These results suggest that one efferent projection from effective stimulation sites for back muscle activation is onto propriospinal neurons in the cervical cord, which in turn project to lumbar cord levels.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

Trunk strength, back muscle endurance and low-back trouble.

The strength and endurance of the trunk muscles was studied in relation to the extent of earlier low-back trouble (LBT) in a homogeneous, and occupationally active group. Twenty-four female and 53 male postmen with an occupational seniority of more than 2 years took part in the investigation. The cumulative lifetime prevalence, the one-year and the point prevalence of LBT were 67%, 62%, and 4% in females and 55%, 52%, and 0% in males. The rates are higher than in a representative Danish population 40 years old. Anthropometrical measurements and isometric strength (MVC) in trunk flexors and extensors were recorded. The flexibility of the spine, hip and knee joints, the fingertip-floor distance, and the restricted extension of the knee were evaluated. The isometric endurance in the trunk extensors was measured by two methods: 1) prone with the unsupported trunk in a horizontal position and the legs and hips fixated to a couch; and 2) standing, at 60% MVC. The participants were divided into three groups according to the extent of previous LBT, Group I: LBT to a degree that made work impossible, Group II: LBT experienced but not to such a degree that work was hindered, and Group III: LBT never experienced. The main findings were that the isometric endurance time of the trunk extensors was shorter in group I than in II and III, while the trunk muscle strength, anthropometrical measures and joint flexibility were independent of the persons' earlier low-back episodes. Differences in the distribution of ST and FT muscle fibres are suggested as an explanation of the endurance difference.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2002

External perturbation of the trunk in standing humans differentially activates components of the medial back muscles.

During voluntary arm movements, the medial back muscles are differentially active. It is not known whether differential activity also occurs when the trunk is perturbed unpredictably, when the earliest responses are initiated by short-latency spinal mechanisms rather than voluntary commands. To assess this, in unpredictable and self-initiated conditions, a weight was dropped into a bucket that was held by the standing subject (n = 7). EMG activity was recorded from the deep (Deep MF), superficial (Sup MF) and lateral (Lat MF) lumbar multifidus, the thoracic erector spinae (ES) and the biceps brachii. With unpredictable perturbations, EMG activity was first noted in the biceps brachii, then the thoracic ES, followed synchronously in the components of the multifidus. During self-initiated perturbations, background EMG in the Deep MF increased two- to threefold, and the latency of the loading response decreased in six out of the seven subjects. In Sup MF and Lat MF, this increase in background EMG was not observed, and the latency of the loading response was increased. Short-latency reflex mechanisms do not cause differential action of the medial back muscles when the trunk is loaded. However, during voluntary tasks the central nervous system exerts a 'tuned response', which involves discrete activity in the deep and superficial components of the medial lumbar muscles in a way that varies according to the biomechanical action of the muscle component.

Adult↗
PubMed1987

[Biomechanical analysis of scoliosis and back muscles using CT evaluation and the finite element method].

The CT observation of back muscles of an idiopathic scoliosis patient showed increased muscle volume and high CT value on the convex side. Following these muscles by digitizer showed that convex muscle volume increased as the vertebra shifted to convexity. These back muscles were suggested to be transversospinalis muscles. Biomechanical analysis using finite element method (FEM) was done to further investigate this increasing volume of back muscles. A Risser experiment using FEM revealed that initial lordosis configuration model only produces rotation to the convex side by unilateral loading. We, therefore, made the model adding posterior element, regarding contraction of M. transversospinalis. In a normal case, the upper vertebra is rotated over the lower towards the side opposite the muscle contraction. The scoliosis model, however, showed rotation towards the side of muscle contraction. M. transversospinalis can be considered as the agent of this rotation force.

Adolescent↗
PubMed1999

Lumbar vertebral angles and back muscle loading with belts.

The study examined belt effects on the change of lumbosacral angle (LSA) and back muscle activity in postures of standing, erect sitting, and slump sitting. We thought that the resulting changes of LSA and back muscle activity when wearing belts with different mechanical characteristics should be different. Eighteen healthy male subjects participated in this study. Though we failed to identify a significant belt effect on the back muscle EMG, the radiographic data revealed an interactive effect of postures and belts on the change of LSA. In standing, the belts increased LSA by increasing almost every lumbar vertebral angle. In erect sitting, the lumbar belt had no effect but the pelvic belt decreased LSA through a decrease in the L1/L3. While sitting slump with a trunk flexion of 15 degrees, both belts increased LSA by restricting the movement of the pelvis. Belt effect on LSA was accompanied with a change of pelvic angle. Significant correlation was found between the backward rotation angles of the pelvis and the angles of LSA (r = 0.692, p < 0.0001), also between the decrease of pelvic angles and the increase of back muscle EMG (r = -0.4, p = 0.017). A change in LSA and pelvic angle after wearing a belt along with posture change seems lead to an increase of the myoelectric activities on the back.

Adult↗
PubMed2001

Intra-operator and inter-operator reliability of surface electromyography in the clinical evaluation of back muscles.

As a prerequisite to the use of a test battery based on electromyographic (EMG) analysis of the paraspinal muscles for identifying and remedying back muscle dysfunction, the intra- and inter-operator reliability was assessed. Fifteen volunteers underwent EMG tests on three occasions. The test subjects were asked to perform 22 exercises, subdivided into four categories: coordination, stabilization, balance and strength exercises. The time interval between the tests was one week. The myoelectric signals of the multifidus (MF) and iliocostalis lumborum pars thoracis (ICLT) were analysed with regard to amplitude (averaged EMG) and frequency (zero cross rate). The results indicated that the reliability was better for the MF than for the ICLT, and also for exercises at higher loads (strength exercises). In the intra-operator condition, the reproducibility of the averaged EMG was good (ICC>0.75), except for the balance exercises (ICC = 0.40-0.74). In general, the averaged EMG in the inter-operator condition and the zero cross rate in both the intra- and inter-operator conditions are less or poorly reliable. These results demonstrate that when back muscle function is evaluated during coordination, stabilization and strength exercises, only the averaged EMG parameter has acceptable reproducibility over time when assessed by the same operator.

Adult↗
PubMed1984

Electromyographic study of lumbar back muscles during locomotion in acute high decerebrate and in low spinal cats.

The electromyographic (EMG) activity of the lumbar back muscles (multifidus, longissimus and iliocostalis) was investigated during treadmill locomotion in acute high decerebrate and in low spinal cats. During alternate stepping (0.7-2.0 m X s-1) in high decerebrate cats, the back muscles have two bursts of activity per step cycle. On the average these EMG bursts last about 170 ms and start some 25 ms before the onset of each vastus lateralis (VL). The two bursts in any one back muscle may have a different duration, the shortest burst on one side coinciding with the longest burst of the homologous contralateral muscle. There is often an overall asymmetry in the discharge wherein the bursts of activity in both ipsi- and contralateral muscles are longer at the onset of one of the VLs. Correlation analyses of several timing parameters of the bursts as a function of walking speeds were made. Different patterns of correlation were identified and it was found that, in most cases, the end of the bursts (with respect to the onset of VL activity) was best correlated with the speed of walking. During gallop, the back muscles activity is a single burst of about 200 ms duration which starts some 75 ms before the onset of VL. In low spinal cats walking after an injection of clonidine, the double burst pattern of EMG activation may be present if there is adequate weight support. However, when the animal steps with the hindlimbs extended and with insufficient weight support, these muscles have a tonic activity uncorrelated with the rhythmic activity of hindlimb muscles.

Animals↗
PubMed1988

Lumbar back muscle activity during locomotion: effects of voluntary modifications of normal trunk movements.

The mechanisms of adaptation of the trunk to changed mechanical conditions were studied during locomotion in man. The myoelectrical (EMG) activity in lumbar back muscles and the movements of the trunk were recorded in nine healthy subjects during walking and running on a motor-driven treadmill. Two different types of voluntary modifications of the movement pattern were used: (1) The trunk was kept in an extreme forward or backward tilted position. In both these situations the basic EMG pattern with two periods of activity per stride cycle was maintained during walking, whereas a major shift relative to the stride cycle (25% of the stride cycle duration) occurred in running with the trunk tilted backwards. The synchrony of the back muscle activation at both sides increased when locomotion was performed with the trunk tilted forwards. The relative duration of the EMG bursts was similar to normal locomotion and corresponded to 15-26% of the stride cycle duration in walking and 23-37% in running. (2) In the other type of modification the subjects were instructed to exaggerate the angular trunk movements either in the sagittal or in the frontal plane. The basic EMG pattern and phase relationships remained in most cases unchanged. One exception was running with exaggerated lateral movements, in which only one period of back muscle activity per stride cycle was observed. The relative duration of the bursts was longer in trials with exaggerated trunk movements as compared to normal locomotion. In walking and running with the trunk tilted forwards or backwards the lumbar back muscles were not always involved as prime movers of the trunk. This was in contrast to the more dynamic situations, in which the back muscle activity appeared to be directly involved in braking and reversing the exaggerated trunk movements.

Adaptation, Physiological↗