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PubMed1978

Morphology and contraction properties of cat lumbar back muscles.

The gross morphology, innervation pattern and contraction properties of lumbar back muscles in the cat were investigated. The medially located multifidi and interspinales are formed by short bundles interconnecting adjacent vertebrae. Laterally located bundles composing longissimus and iliocostalis are attached to the spinous processes by a fascial layer and to the pelvic bone by a well developed intermuscular septum. Different spinal segments innervate the various sections along the muscles in such a way that the myotomes composing a muscle belly seem to be arranged after one another, in a row. The contraction time of a maximal isometric twitch is 34 ms for multifidi and interspinales and 29 ms for longissimus and iliocostalis. No large segmental variations of contraction times were found. The time course of twitch responses and a study of reflex contractions in middle and lower sections of lateral muscles indicate the presence also of a slowly contracting portion located to the longissimus. The initial muscle length is more decisive for the twitch amplitude of medial than of lateral muscles. In medial muscles summation of individual twitches starts at a stimulus frequency of 10--15 Hz and apparent fusion occurs at about 50 Hz. For lateral muscles corresponding values are 15--20 Hz and about 70 Hz. The contractile tension declines markedly in all muscles during a 10 min period of stimulation at 5 Hz.

Animals↗

PubMed2000

Fos expression in the rat brain and spinal cord evoked by noxious stimulation to low back muscle and skin.

STUDY DESIGN: Acute noxious stimulation delivered to lumbar muscles and skin of rats was used to study Fos expression patterns in the brain and spinal cord. OBJECTIVES: The present study was conducted to determine the differences in Fos expression in the brain and spinal cord as evoked by stimuli delivered to lumbar muscles and skin in rats. SUMMARY OF BACKGROUND DATA: Patients with low back pain sometimes show psychological symptoms, such as quiescence, loss of interest, decreased activities, appetite loss, and restlessness. The pathway of deep somatic pain to the brain has been reported to be different from that of cutaneous pain. However, Fos expression has not been studied in the central nervous systems after stimulation of low back muscles. METHODS: Rats were injected with 100 L of 5% formalin into the multifidus muscle (deep pain group; n = 10) and into the back skin of the L5 dermatome (cutaneous pain group; n = 10). Two hours after injection, the distribution of Fos-immunoreactive neurons was studied in the brain and spinal cord. RESULTS: Fos-immunoreactive neurons were observed in laminae I-V in the spinal cord in the cutaneous pain group, but they were not seen in lamina II in the deep pain group. In the brain, Fos-immunoreactive neurons were significantly more numerous in the deep pain group than in the cutaneous pain group in the piriform cortex, the accumbens nucleus core, the basolateral nucleus of amygdala, the paraventricular hypothalamic nucleus, the ventral tegmental area, and the ventrolateral periaqueductal gray. CONCLUSION: The finding that Fos-immunoreactive neurons were absent from lamina II of the spinal cord in the deep pain group is similar to that of the projection pattern of the visceral pain pathway. Fos expression in the ventrolateral periaqueductal gray in the deep pain group may represent a reaction of quiescence and a loss of interest, activities, or appetite. Furthermore, the detection of large numbers of Fos-immunoreactive neurons in the core of accumbens nucleus, basolateral nucleus of amygdala, paraventricular hypothalamic nucleus, and ventral tegmental area in the deep pain group may suggest a dominant reaction of dopaminergic neurons to stress, and a different information processing pathway than from that of cutaneous pain.

Animals↗

PubMed1976

Exteroceptive influences on the lumbar back muscle tone and reflexes in the cat.

The exteroceptive influences on tonic activity and on stretch reflexes of the longissimus dorsi and multifidus spinae muscles were investiagted in decerebrate, spinal and chloralose-anesthetized cats. Adequate skin stimulation was used to map out facilitatory and inhibitory skin areas on the trunk and the extremities. On the trunk facilitatory areas are relatively large and located at the dorsal side while inhibitory areas are confined to the ventrolateral part of the contralateral body half. The facilitatory skin fields are of approximately the same size in decerebrate and spinal cats. On leg skin stimulation facilitation can be evoked from the ipsilateral hind limb while inhibition results from stimulation of the other limbs. Spinal cord transection increased excitatory effects of ipsilateral hind limb stimulation. Reflex responses in the back muscles to applied stretch are described. These reflexes were used as test reflexes in experiments with conditioning stimulation of the peripheral nerves supplying skin areas from which effects on back muscle activity were evoked by adequate stimulation. The conditioning-test experiments and those using adequate stimulation show that the longissimus dorsi and multifidus spinae are activated or facilitated by an ipsilateral stimulus to skin afferents. The extent of the effects induced by stimulation of skin differs in the types of preparation used. These differences may be accounted for by assuming a supraspinal control of the reflex pathways studied.

Anesthesia, General↗

PubMed1992

Lumbar disc and back muscle degeneration on MRI: correlation to age and body mass.

Lumbar intervertebral discs and paraspinal muscles in 74 healthy volunteers ranging in age from 19 to 74 years were evaluated with MRI, and the occurrence of degeneration was correlated to age and body mass. Muscle size and the amount of fat in the muscles was studied from MRI cross sections. When the back muscles were degenerated, they were small and contained fat deposits. By contrast, the psoas muscles never showed gross fat deposits. Degeneration of both the lumbar discs and muscles increased with age. No correlation was found between muscle degeneration and overweight. Muscle degeneration is as common as disc degeneration in the lumbar area. MRI is an excellent method to assess both muscle and disc degeneration.

Adipose Tissue↗

PubMed1998

Repetitive lifting tasks fatigue the back muscles and increase the bending moment acting on the lumbar spine.

During manual handling, the back muscles protect the spine from excessive flexion, but in doing so impose a high compressive force on it. Epidemiological links between back pain and repetitive lifting suggest that fatigued muscles may adversely affect the balance between bending and compression. Fifteen volunteers lifted and lowered a 10 kg weight from floor to waist height 100 times. Throughout this task, the bending moment acting on the osteoligamentous lumbar spine was estimated from continuous measurements of lumbar flexion, obtained using the 3-Space Isotrak. Spinal compression was estimated from the electromyographic (EMG) activity of the erector spinae muscles, recorded from skin-surface electrodes at the levels of T10 and L3. EMG signals were calibrated against force when subjects pulled up on a load cell, and correction factors were applied to account for changes in muscle length and contraction velocity. Fatigue in the erector spinae muscles was quantified by comparing the frequency content of their EMG signal during static contractions performed before, and immediately after, the 100 lifts. Results showed that peak lumbar flexion increased during the 100 lifts from 83.3 +/- 14.8% to 90.4 +/- 14.3%, resulting in a 36% increase in estimated peak bending moment acting on the lumbar spine (P = 0.008). Peak spinal compression fell by 11% (p = 0.007). The median frequency of the EMG signal at L3 decreased by 5.5% following the 100 lifts (p = 0.042) confirming that the erector spinae were fatigued, but measures of fatigue showed no significant correlation with increased bending. We conclude that repetitive lifting induces measurable fatigue in the erector spinae muscles, and substantially increases the bending moment acting on the lumbar spine.

Adult↗

PubMed1985

Relationships between strength of low back muscle contraction and reported intensity of chronic low back pain.

The electromyographic patterns produced by recording the left and right paraspinal muscles of subjects while in motion (bending and rising) and still (standing upright, sitting supported and unsupported, and prone) were contrasted for people with: 1) no history of back pain; 2) past episodes of low back pain but currently pain free; and 3) chronic low back pain with various diagnosed etiologies. Each of the 83 individuals recorded during episodes of low back pain produced a unique pattern of muscle contraction which was relatively stable between weekly recording sessions. In every case, at least one of the six positions showed elevated contraction levels significantly above that of the 15 subjects with no history of back pain and the 28 with no current back pain. For nine of the eleven subjects who reported changes in pain intensity between recording sessions, a clearly positive correlation occurred between the reported intensity of pain and the level of contraction in the one position most different from the reference group. No diagnostic subgroup of low back pain subjects produced a single unique pattern. Furthermore, no single aspect of the EMG signal, such as bilateral asymmetry, had predictive value for any individual subject. Our recordings did not differ with respect to diagnostic category so further research will have to be done to determine whether the diagnostic categories currently in use do not fit the physiological bases for the problems and/or whether prolonged abnormal levels of muscle contraction eventually produce problems such as disc displacement.

Adolescent↗

PubMed2006

[Evaluation of back muscle function based on EMG time-frequency spectrogram analysis].

EMG has been extensively used to study function of back muscle, which plays an important role in the objective assessment of occupational low back pain, yet the inherent large variability of EMG signals across subjects produced by reasons already known or unknown may mask true biological differences. Some useful parameters abstracted from 8-channel EMG signal in time-frequency domain are used or proposed and calculated in this paper to decrease this variability, when comparing the possible difference between low back pain patients and normal control group. The calculation of instantaneous median frequency is improved to decrease the interruption of background noise, and different power densities in EMG time-frequency spectrogram are observed in two tested groups.

Back↗

PubMed1977

Quantitative electromyographic studies of back muscle activity relatated to posture and loading.

The myoelectric activity of some of the posterior muscles of the back was studied quantitatively using signal amplitude estimation and power spectrum analysis. Surface electrodes were placed on both sides of the trunk at T4, T8, L1, L3, and L5 levels. Four different angles of forward flexion were studied during external loading of the spine with 200 N. At 30 degrees of forward flexion studies were made when the load was increased from 0 to 300 N. Asymmetric loading was studied with the trunk erect, in lateral flexion, and in rotation. The myoelectric activity increased when the angle of flexion increased and when the external load was increaed at a fixed angle of flexion. During asymmetric loading, comparatively higher activity was found on the contralateral side in the lumbar region and on the ipsilateral side in the thoracic region. The magnitude of the power spectrum changes correlated well with the amplitude of the myoelectric signal. Spectral changes increased when the signal amplitude increased, indicating localized muscle fatigue.

Adult↗

PubMed2004

[Analysis of surface electromyography on repetitive lifting task-induced fatigue of back muscles].

OBJECTIVE: Using surface electromyography (SEMG) technique to evaluate repetitive lifting task-induced fatigue of back muscles. METHODS: Thirteen volunteers lifted and lowered an 8 kg weight from floor to waist level for 100 times. Fatigue in the erector spinae muscles was quantified by comparing the frequency content of the EMG signal during static contractions performed before, and immediately after the 100 lifts. RESULTS: EMG average amplitude rose gradually during 100 lifts, the difference was significant at T10 right (P < 0.05) and L3 left (P < 0.01), the difference was not significant at T10 left and L3 right (P > 0.05). The median frequency intercept at T10 right, T10 left, L3 right, L3 left erector spinae muscles decreased by 2.0% (P > 0.05) 10.9% and 29.9% (P < 0.05), 27.9% (P < 0.01), respectively. The mean power frequency intercept decreased by 9% at L3 left erector spinae muscle (P < 0.05), the decrease was not statistically significant at other sites (P > 0.05). CONCLUSION: Repetitive lifting may induce measurable fatigue in the erector spinae muscles. Erector spinae muscle at L3 is more easily fatigued than at T10. Using the median frequency intercept to assess muscle fatigue is more sensitive than using mean power frequency intercept.

Adult↗

PubMed2005

The effect of delayed-onset muscle soreness on stretch reflexes in human low back muscles.

The aim of the study was to investigate the effect of moderate delayed-onset muscle soreness (DOMS) on the short latency stretch reflex (SLR) and long latency stretch reflex (LLR) response i.e. electromyographic (EMG) onset latencies and EMG amplitudes in erector spinae (ES). Nine males with muscle soreness (DOMS group) were tested 24, 48 h, and 7 days post-exercise. Eight males (control group) were tested likewise. EMG was measured from ES bilaterally at the level of L3/L4. The SLR was elicited by mechanically tapping the ES at L3/L4, and the LLR was elicited by sudden loadings of the spine. Significant reductions in force during maximal voluntary contractions and range of motion, and a significant increase in muscle soreness (measured by pressure algometry) and subjective experience of soreness in the low back indicated DOMS 24, and 48 h post-exercise in the DOMS group. No changes were observed in the control group. The SLR and LLR response were unaffected by DOMS, i.e. no changes in EMG latencies and amplitudes were observed. In conclusion, despite changes in DOMS indicators, the reflex system protecting the stability of the lumbar spine is apparently capable of maintaining an appropriate triggering of SLR and LLR.

Adult↗

PubMed2004

Back muscle EMG of helicopter pilots in flight: effects of fatigue, vibration, and posture.

INTRODUCTION: The high prevalence of low back pain in helicopter pilots has been attributed to back muscle fatigue due to a pilot's required posture and/or aircraft vibration. This study investigated the effect of posture and vibration on the surface electromyogram (EMG) of right and left erector spinae (ES) muscles of pilots and evaluated ES fatigue during flight. METHODS: There were 12 male pilots who were monitored during helicopter flights lasting an average of 2 h. Prior to the flight, a maximal voluntary contraction (MVC) of ES was performed and the EMG was recorded. Vibration was measured at the pilot's seat through a triaxial accelerometer. The effect of posture on EMG was tested by comparing four characteristics of left and right EMG expressed as % MVC. Effect of Z vibration on EMG was investigated by coherence function and through correlation between coherently averaged EMG and Z for the frequencies of the main rotor of the helicopter (1R) and its first harmonic (2R). Fatigue was investigated through median frequencies (MF) of the EMG power spectra. RESULTS: No effect of posture on EMG was found for any parameter (p > 0.05). Data from one pilot suggested an effect of 1R on EMG, but statistical tests revealed this not to be significant (p > 0.05) for any pilot. No fatigue was evidenced by linear regression of MF. CONCLUSION: While the scientific literature contains the hypothesis that low back pain in helicopter pilots is mainly due to muscle fatigue caused by posture and/or vibration, the present study did not lend support to this hypothesis.

Acceleration↗

PubMed2001

A functional subdivision of hip, abdominal, and back muscles during asymmetric lifting.

STUDY DESIGN: An experimental study of muscle recruitment patterns during asymmetric lifting in healthy individuals. OBJECTIVE: To investigate muscle recruitment patterns during asymmetric lifting, representing a common daily living activity, to determine whether systematic differences exist between functioning of the local and global muscle systems. SUMMARY OF BACKGROUND DATA: The normal function of the local muscle system is to provide sufficient segmental stability to the spine. The global muscle system provides general trunk stabilization and enables the static and dynamic work necessary for daily living and sports activities. Current knowledge about these two muscle groups appears to be specifically derived from anatomic findings and experiments conducted under artificial circumstances. To the authors' knowledge, the recruitment patterns of both muscle groups have not been investigated in daily living activities. METHODS: Twenty-nine healthy individuals performed different variants of asymmetric lifting activities. Electromyographic data were collected from seven hip, abdominal, and back muscle pairs. In addition, trunk kinematics were measured by means of an ultrasonic movement analysis system. RESULTS: The left and right obliquus internus, rectus femoris, and multifidus showed symmetric co-contraction in all variants of activities. In contrast, significant left/right differences were observed in the external oblique, gluteus maximus, iliocostalis lumborum pars thoracis, and latissimus dorsi. CONCLUSIONS: The results of this study show a symmetric activation of the local muscles during the performance of low-load, asymmetric lifting tasks, which suggests that these muscles play a stabilizing role during these manoeuvres. The global muscles, however, hand show asymmetric patterns of activation during the same tasks, supporting their role as global stabilizers and prime movers.

Abdominal Muscles↗

PubMed2000

A cortical motor region that represents the cutaneous back muscles in the macaque monkey.

A cortical motor region that represented the cutaneous muscles on the back was identified on the medial wall of the frontal lobe in the macaque monkey. In this region, neurons responded to somatosensory stimuli such as light touch or squeezing of the back skin, and intracortical microstimulation elicited contraction of the back skin. Such a region was located primarily on the dorsal bank of the cingulate sulcus, corresponding to the dorsal cingulate motor area.

Animals↗

PubMed2001

Back muscle fatigability is associated with knee extensor inhibition in subjects with low back pain.

STUDY DESIGN: Cross-sectional study of 25 male golfers with chronic low back pain and 16 healthy controls of similar age. OBJECTIVES: To assess the association between functional capacity of the back extensors and the quadriceps muscles. SUMMARY OF BACKGROUND DATA: Chronic low back pain has been shown to lead to changes in muscle activation patterns of the abdominals and the gluteus maximus. The effect of chronic low back pain on lower limb function has not been investigated. METHODS: Back extensor endurance was assessed by a Biering-Sørensen test; surface EMG was measured bilaterally on the erector spinae at T12 and L4--L5. Muscle inhibition in the quadriceps was assessed by applying an electrical twitch to the maximally contracted muscle. The associations between holding time, decrease in EMG median frequency (i.e., the slope of the regression line on median frequency vs. time), and muscle inhibition were compared for study participants with chronic low back pain and controls. RESULTS: Mean back extensor holding times were 88 +/- 30 seconds for study participants with chronic low back pain and 92 +/- 17 seconds for controls. Both groups showed bilaterally similar decreases in EMG median frequency at L4--L5 and T12; however, the slopes were significantly steeper at L4--L5 than T12. Study participants with chronic low back pain with poor back endurance had significantly higher muscle inhibition compared with study participants with chronic low back pain with good back endurance, whereas such an association was not evident in healthy controls. CONCLUSIONS: In golfers with chronic low back pain reduced back endurance was associated with significant inhibition of the knee extensors, indicating that this muscle group cannot be activated to a full extent. These findings suggest a possible association between back extensor fatigability and knee extensor dysfunction in male golfers with chronic low back pain.

Adult↗

PubMed1989

Elastic strain energy in the low back muscles during human walking.

A simple model of the thorax, pelvis and three columns of the intrinsic lumbar back muscles (= ILBM) was constructed. The model was used to study the length of the ILBM during the different stages of the walking cycle. The length of the right ILBM (especially the lateral column) was largest at right toe off, exactly the stage of the walking cycle in which most force was needed to prevent the torso from falling forwards and laterally.

Back↗

PubMedDate not supplied

Intradiskal pressure, intra-abdominal pressure and myoelectric back muscle activity related to posture and loading.

Intradiskal pressures, intra-abdominal pressures and myoelectric activities of posterior back muscles have been measured simultaneously in vivo in 4 subjects. Five different angles of forward flexion were studied while externally loading the trunk with 200N. At 30 degrees of forward flexion studies were made when the load was increased from 0 to 300N. Asymmetric loading was studied with the trunk erect, in lateral flexion and in rotation. The measurement parameter values all increased when the angle of flexion increased and when the external load was increased at a fixed angle of flexion. Linear relationships were established. During asymmetric loading pressure values and the myoelectric activity increased. The increase in myoelectric activity was comparatively greater on the contralateral side of the lumbar region and on the ipsilateral side of the thoracic region. The disk pressure, the intra-abdominal pressure, and the FRA-values were higher throughout when the trunk was loaded in rotation, than in lateral flexion.

Abdomen↗

PubMed2001

Functional roles of abdominal and back muscles during isometric axial rotation of the trunk.

Electromyographic (EMG) studies have shown that a large number of trunk muscles are recruited during axial rotation. The functional roles of these trunk muscles in axial rotation are multiple and have not been well investigated. In addition, there is no information on the coupling torque at different exertion levels during axial rotation. The aim of the study was to investigate the functional roles of rectus abdominis, external oblique, internal oblique, latissimus dorsi, iliocostalis lumborum and multifidus during isometric right and left axial rotation at 100%, 70%, 50% and 30% maximum voluntary contractions (MVC) in a standing position. The coupling torques in sagittal and coronal planes were measured during axial rotation to examine the coupling nature of torque at different levels of exertions. Results showed that the coupled sagittal torque switches from nil to flexion at maximum exertion of axial rotation. Generally, higher EMG activities were shown at higher exertion levels for all the trunk muscles. Significant differences in activity between the right and left axial rotation exertions were demonstrated in external oblique, internal oblique, latissimus dorsi and iliocostalis lumborum while no difference was shown in rectus abdominis and multifidus. These results demonstrated the different functional roles of trunk muscles during axial rotation. This is important considering that the abdominal and back muscles not only produce torque but also maintain the spinal posture and stability during axial rotation exertions. The changing coupling torque direction in the sagittal plane when submaximal to maximal exertions were compared may indicate the complex nature of the kinetic coupling of trunk muscles.

Abdominal Muscles↗

PubMed1999

Toward a better prescription of the prone back extension exercise to strengthen the back muscles.

This study investigated the level of resistance and the level of muscle activation of the prone back exercise. Fifteen male subjects with no previous history of low back injury performed two repetitions of seven exercises. These consisted of four maximal isometric voluntary contractions (MVC) and three prone back extension (PBE) exercises. The subject was lying prone on a table, the upper body was suspended off the end of the table and the legs and thighs were secured to the table with straps. Three starting positions from the horizontal were investigated, 0 degree, 30 degrees and 60 degrees, and were compared with MVC to quantify the level of effort needed to perform the task. The results showed that the three PBE exercises require a level of resistance and a level of muscle activation generally under 40% of the maximum capacity of healthy subjects. Muscle activity of the erector spinae (ES) was slightly greater when the exercise started at 60 degrees, compared to 0 degree and 30 degrees. During the static phase of the PBE exercises, the level of resistance remained at 40% relative to the peak reaction moment of the MVC, but muscular activity of ES tended to work at a lower activity level. In conclusion, since for healthy subjects PBE exercises are low resistance exercises, they seem to be more specifically designed to develop muscular endurance of the back muscles.

Adult↗