The aim of this study was to evaluate and clarify the usefulness of different spectral characteristics of myoelectrical activity in the follow-up of development of muscle fatigue. Vastus lateralis (part of quadriceps) muscle loaded in a simple isokinetic exertion test was used as a model. Twelve, well trained athletes served as study subjective to minimize the inter-individual variations. They went through one-minute test with isokinetic device at the range of 90 degrees extension and flexion at the level of their maximal force. The myoelectrical signals were registered from middle of the vastus lateralis muscle by a computerized fast Fourier transform analyzing system based on 80286 and 80287 microprocessors and using surface electrodes. Mean power frequency (MPF) was 65.6 (SE=Standard Error, 1.6) Hz, median frequency (MF) 55.8 Hz and zero crossing rate (ZCR) 92.5 (SE 1.5) during first performance. All these parameters decreased apparently linearly and significantly from the beginning of the test (P<0.001). The decrease rate of ZCR was fastest and MF slowest. The area of power spectrum (PSA) was 1753 (SE 320) units during first performance, and it increased markedly with slightly accelerating rate during the test. In conclusion, for the evaluation of the muscular performance during the development of fatigue it is beneficial to monitor simultaneously MPF, MF and ZCR.

OBJECTIVE:To assess low back pain (LBP) intensity and subjective disability during pregnancy and compare the pain scores with lumbar motion patterns. DESIGN:A prospective study of pregnant back pain sufferers and healthy controls. SETTING:Kuopio University Hospital, Kuopio, Finland. PARTICIPANTS:Study group consisted of 32 pregnant women with LBP; control group consisted of 21 healthy pregnant women. MAIN OUTCOME MEASURES:Back pain intensity was assessed by visual analog scale (VAS), and subjective disability index was measured by Oswestry Low Back Disability Questionnaire, at 20 and 36 weeks of pregnancy. Back muscle activities were recorded by surface electromyography, and movement sensors were used to detect lumbar motion. RESULTS:In the study group current pain scores (VAS) at first and last trimester correlated strongly (r = .82, p < .00). Pain scores correlated with body weight at the first trimester (r = .54, p = .003) and at the last trimester (r = .67, p < .00). Significant correlation was noted between current pain intensity and back muscle activity level during forward body flexion at first trimester (r = .704, p < .00). Back muscle activity during bending measured at first trimester significantly correlated with pain intensity at last trimester (r = .703, p < .00). Back muscle activity during the first trimester of pregnancy had a negative correlation with current (r = -.57, p = .002) and later subjective disability index (r = -.42, p = .02). It correlated inversely (r = -.54, p = .003) with pain score at last trimester of pregnancy, ie, the lower the back muscle activity at the beginning of pregnancy, the more pain and disability throughout pregnancy. In the control group, three women developed LBP and disability feelings during pregnancy. They had increased muscle activity during flexion at delivery, ie, disturbed flexion relaxation. CONCLUSIONS:Prepregnancy LBP predicts renewed pain during pregnancy, and dysfunction of back muscles has been established in LBP. In this study, disturbance in the relaxation of the back muscles was linearly related to current, and also to later, pain scores. In addition, back muscle activity level was inversely related to the disability index. For the first time, it has been shown prospectively that the function pattern of back extensors seems to predict, and is related to, future back pain. Simple function testing is promising and might be valuable in identifying mothers with a high risk of pregnancy-related back pain and in directing preventive intervention to high risk women by making them aware of self-treatment methods.

STUDY DESIGN A cross-sectional analysis was done of patients with recurrent low back pain referring to the lower limbs. OBJECTIVES To analyze dynamic radiographs of forward and backward bending of the lumbar back and to determine, using routine neurophysiologic measurements, the functional state of the lower nerve roots in patients with recurrent low back pain radiating to the lower limbs. METHODS Clinical and neurophysiologic studies showed eight of the 108 patients with low back pain to have ventral root impingement at either L5 or S1 level. The remaining 100 patients, 56 women and 44 men (mean age, 37.6 years; range, 17-62 years), made up the study group for continuing investigation. History of low back pain ranged from 4 months to 20 years. RESULTS Disturbed intervertebral movement was found in 51 of 100 patients. Twenty-seven percent had L5 or L4 anterolisthetic hypermobility, and 35% had L4 or L3 vertebral retrolisthesis. Vaguely delineated radiating sensations in the lower limbs were common (62%). Back muscle electromyographs were mostly (86%) normal in patients whose low back pain was localized. Conversely, almost three-fourths of those experiencing radiating or referred pain had abnormal electromyographs, consistent with a mild degree of axonal damage in the posterior branch of the lumbar nerve root innervating the medial paraspinal muscles. This finding was most common among patients with retrolisthesis and simultaneous degenerative changes. CONCLUSIONS Evaluation of low back pain should include tests for degenerative retrolisthesis, especially in patients experiencing radiating sensations with no evidence of root impingement, because abnormal electromyographic findings showing denervation of the paraspinal muscles was most common in patients with degenerative retrolisthesis. To improve the functional support of the lumbar region, rehabilitation should be directed to the medial back muscles because they provide the most effective support for intervertebral motion and because mild disturbances appear to be associated with their innervation in recurrent low back pain.

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 con 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 lime 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. (C) 1997 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation.

It has been widely observed that the outcome after repeat lumbar surgery is rarely comparable to that of primary surgery. In particular, the results of repeat surgery for lumbar spinal stenosis (LSS) have not been favourable. We used a matched-pair format in an attempt to decrease the confounding factors so as to determine as exactly as possible the effect of prior back surgery on the LSS patients' surgical outcome. The matching criteria were sex, age, myelographic findings, major symptom, and duration of symptoms. From one group of 251 patients without prior back surgery (SO patients) and another of fifty-three patients with one preceding back operation (RS patients), forty-one similar matched patients pairs (one SO and one RS-patient) were formed.There were 8 female and 33 male pairs. The mean age of the SO patients was 51.6 and of the RS patient 51.4 years, and the mean follow-up time was 4.6 and 4.4 years. The assessment of outcome was based on a subjective disability questionnaire. The SO patients fared significantly better than the RS patients (32.1 versus 41.3, P=0.026). A short time interval between operations in the RS patients had a worsening effect on outcome, but this trend was not significant.We concluded that one preceding back operation had a worsening effect on the outcome of patients operated on for LSS. As a whole, the results of RS patients were unfavourable. The proper time for achieving good surgical results in LSS patients is the initial operation.

Results of decompressive surgery for lumbar spinal stenosis vary. We evaluated the density of lumbar muscles by computed tomography (CT) at the L2–L4 levels in patients 4 years after they had undergone surgery for lumbar spinal stenosis. Twenty of these patients had an excellent outcome clinically, and 16 patients had very poor outcome. The residual stenosis and density of lumbar muscles in Hounsfield units were measured on CT images. The clinical evaluation of outcome also included the Oswestry questionnaire and a walking test. The density of lumbar flexors was higher in the group with excellent results than in the group with poor results. The density of lumbar extensors showed a marked decrease in the operated area. These results suggest that the decrease of muscular density can be partially explained by disuse or inactivity. The decrease in the operated area probably reflects muscular atrophy caused by muscle denervation.

Nerves leave the spinal cord as mainly motor primary rootlets and sensory rootlets. These join to nerve root before leaving the spinal canal. After the root canal, the nerve root branches into the ventral root, which contains sensory and motor fibers innervating the extremities, and the dorsal root, that is, the dorsal ramus, which innervates the posterior structures, for example, back muscles: the dorsal ramus itself may become irritated (dorsal ramus syndrome). Especially predisposed to entrapment is the medial branch of the dorsal ramus, which innervates the multifidus muscle and also contains pain fibers. Here we describe the influence of local anesthesia and back-muscle-training therapy on subjective and objective pain parameters in 21 low-back-pain patients who had similar clinical status and neurophysiologic findings and whose recurrent low back pain was most apparently associated with dorsal ramus neuropathy, without any radiologic or neurophysiologic evidence of more proximal ventral nerve root damage in the spinal cord or at the nerve root origin. After treatment, all were pain free and back muscle activity during lumbar-pelvic rhythm was normalized.

Study Design. This retrospective study was designed to investigate the effects of previous back surgery in patients undergoing surgical procedure for lumbar spinal stenosis.Objectives. The authors evaluated the results of singly operated and repeat surgery patients operated on for lumbar spinal stenosis, and compared prognostic factors correlated with the results for these two groups.Summary of Background Data. Repeat back surgery is generally not as successful as a first operation, but few studies evaluate the effects of previous back surgery on the surgical outcome of patients with lumbar spinal stenosis.Methods. The subjective disability of singly operated and repeat surgery patients as assessed by the Oswestry questionnaire was compared with clinical data and myelographic findings to identify factors predictive of outcome.Results. The mean Oswestry score was 31.0 for singly operated patients and 40.9 for repeat surgery patients (P = 0.0001). The outcome was excellent-to-good in 67% of singly operated patients and in 46% of repeat surgery ones (P < 0.0017). Severe myelographic findings correlated significantly with good outcome in the singly operated group but not in the repeat surgery group. Coexisting disease contributed significantly to poor outcome in the repeat surgery group, but not in the singly operated group. The optimum time interval for achieving successful results from subsequent surgery is at least 18 months after previous surgery. In the regression analysis, the prognostic preoperative variables for good outcome was block stenosis on myelography in the singly operated patients and age over 50 years and no coexisting disease in the repeat surgery patients.Conclusions. Previous back surgery had a highly significant worsening effect on the outcome of patients reoperated on for lumbar spinal stenosis. Not even a very well-established diagnosis of lumbar spinal stenosis, as confirmed by myelography and during surgery, could guarantee as successful a surgical outcome in the repeat surgery patients as that in the singly operated patients.

Flexion-extension and traction-compression radiographs as well as functional electromyographic (EMG) analysis were used to assess nine patients with chronic low back pain and segmental instability symptoms. After a treatment program, at which time most of the patients were asymptomatic and their physical status normalized, the patients were reexamined using EMG and radiographs. No significant change was found in the functional radiographic examination, whereas the myographic findings were significantly improved. Although the number of subjects was small, the results suggest that radiographic findings correlate poorly with clinical findings. Because of the improvement of the physical and myographic findings, the term "segmental dysfunction" may better describe the disability and symptoms than does the term "segmental instability."

Impairment and disability after back surgery is a common diagnostic and therapeutic problem. For the most part the reasons are unclear. Of 178 patients who had undergone laminectomies 2-5 years earlier, 14 patients with good recovery and 21 patients with poor recovery but no evidence of restenosis on computed tomography were selected by the Oswestry index. According to radiologic, neurophysiologic, and muscle biopsy evidence most patients (13 of 15 studied) suffering from the severe postoperative failed back syndrome had dorsal ramus lesions in one or more segments covered by the scar and local paraspinal muscle atrophy at the corresponding segments. Disturbed back muscle innervation and loss of muscular support leads to the disability and increased biomechanical strain and might be one important cause to the failed back syndrome. It may be possible to develop operating techniques that save back muscle innervation better than the usual ones.

Surface rms-EMG measurement as a real time monitoring method for detecting the anaerobic threshold during a bicycle ergometer test was evaluated and compared with blood lactate and ventilatory parameters. The study group consisted of 12 healthy ice hockey players. The anaerobic threshold indicated as dislinearity of increase in blood lactate level, ventilatory parameters and myoelectrical activity was observed at the work level of 300 (range 270-330) W in each case. The linearity disappeared at same time in the rms-EMG-load ratio both in working (quadriceps and gastrocnemius) and nonworking (frontalis) muscles. The rms-EMG follow-up was easier to perform than measurements of blood lactate and ventilatory parameters.

The causes of recurrent and chronic low back pain usually remain unknown. The dorsal ramus lesion was found in 57 of 200 low back pain patients in this study in L5 or L4 segment without any neurophysiologic or neuroradiologic evidence of proximal ventral root compression. The neuropathy of dorsal rami, especially in their medial branches seems to be surprisingly common finding associated with low back pain and referred symptoms.

UNLABELLED:The functioning of low back muscles of back pain patients during flexion and reextension has not been properly investigated. In this study, we analyzed rectified, averaged electric activity (RMS EMG) and corresponding raw intramuscular (IM) EMG from lumbar paraspinal muscles to quantify the activity level during simple bending cycles in 87 back pain patients compared to 25 able-bodied controls.THE RESULTS:All functional phases seen in raw IM EMG were also shown in surface RMS EMG. Surface RMS EMG pattern seems to yield more information from activity level than IM EMG pattern. The RMS EMG patterns of back pain patients differed from those of controls as follows: (1) There was clearly noticeable activity during standing in back pain patients. (2) There was only a partial decrease of EMG activity after flexion in back pain patients with current pain. (3) The ratio of mean reached at maximal activity level during extension and flexion was less in patients (1.8, SD = 0.5, p less than .001) than able-bodied controls (3.2, SD = 0.8). (4) Segmental differences were observed in IM EMG activities in patients having hypermobility in bending x-ray. (5) Large peak potentials occurred during movements in patients having segmental hypermobility. THE RESULTS indicate that averaged surface recording is a valuable tool in the investigation of dynamic spine functions in back pain patients.

Low back pain patients (N = 18) having segmental hypermobility in one lumbar segment and healthy controls (N = 13) were chosen for this study. Patients had no other structural spinal pathology except displacement of one vertebra to another in lateral X-ray bending pictures. Kinetic intramuscular EMG-activity from paraspinal muscles was studied off-line during back flexion and reextension. Routine needle EMG study of paraspinal muscles was also performed in addition to measurements of the tibial nerve H-reflexes and peroneal F-responses. Results showed that the number of MUAPs in erector spinae muscle on voluntary efforts was rarefied at hypermobile levels, and spontaneous activity, positive sharp waves and high frequency discharges were found in more than half of the patients in paraspinal muscles, usually at hypermobile levels only. No signs of proximal nerve root compression were found. This indicates neuropathy of dorsal rami at the instable level.

The loading of wordprocessor workers was followed over a four month period of a re-education course with the aid of electromyography of the trapezius and frontalis muscles in order to study the effect of learning. Working with the word processor increased the electrical activities in both muscles. The increase did not diminish with the learning of the work. On the contrary the electrical activity increased significantly in the frontalis muscle. Intervening gymnastics during work decreased the electrical activities. The screen (on/off) did not affect the activity. Most effective in lowering the myoelectrical activity in both muscles were the armsupports. A significant positive linear correlation was observed in the electrical activities of the trapezius and frontalis muscles both at rest and during wordprocessor work.

1. On-line monitoring of surface rms-EMG for detecting the anaerobic threshold during a cycle ergometer test was evaluated and compared with blood lactate and ventilatory parameters in 12 healthy icehockey players. 2. Dislinearity of increase in blood lactate level, ventilatory parameters and myoelectrical activity was observed at the mean work level of 300 (range 270-330) watts in each case. 3. The linearity disappeared at the same time in the rms-EMG-load ratio in working quadriceps and gastrocnemius muscles while also in nonworking frontalis muscle a change in EMG level was noticed. 4. The break point in rms-EMG did not correlate with the changes in skin humidity and temperature. No change was observed in spectral properties of the myoelectrical signals. 5. The rms-EMG follow-up is easier to perform than measurements of blood lactate and ventilatory parameters in the determination of anaerobic threshold.