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PubMed2000

Back muscle fatigue in healthy men and women studied by electromyography spectral parameters and subjective ratings.

To obtain reference data for future studies of patients with low back pain, back muscle fatigue was studied by surface electromyography at L1 and L5 lumbar levels in 55 healthy subjects exerting 80% of maximal voluntary contraction of the back extensors in a sitting position. Reference data were the initial value and rate of decrease (slope) of the median frequency during the contraction. The aim was also to study the effects of contraction time, gender differences, electrode locations and correlations with torque, age and subjective ratings. Initial median frequency was 52 Hz +/- 7.5, with no difference between electrode locations; steeper slopes were found at L5 level (-0.44%/s +/- 0.25) than at L1 (-0.36%/s +/- 0.26). No right-left differences and no gender differences were found for these parameters. A correlation was observed between slope and initial median frequency, higher for men (r approximately -0.7) than for women (r approximately -0.5). Intersubject coefficient of variation for the slope was smallest for the longest (45 seconds) recording time (60-70%), but still much higher than for the initial median frequency (14%). The torque and the subjective ratings of fatigue showed no correlation with the electromyography variables. We conclude that the same reference values can be used for men and women. Owing to the large intersubject range of the slope, the clinical use of this variable may, however, be impeded.

Adult↗
PubMed1988

Physical activity in postmenopausal women: effect on back muscle strength and bone mineral density of the spine.

In this cross-sectional study, the bone mineral density of the lumbar spine, the back extensor strength, and the level of physical activity were determined in 68 healthy, postmenopausal women. Physical activity was determined by a graded questionnaire and varied from sedentary to heavy vocational and avocational activity levels. Bone mineral density (L2 through L4) was measured with dual-photon absorptiometry. Back extensor strength was determined with use of a strain-gauge dynamometer. Bone mineral density ranged from 0.77 to 1.49g/cm2 (mean +/- SD, 1.06 +/- 0.18g/cm2). Back extensor strength ranged from 37 to 145 lb (84.6 +/- 23.5 lb). Physical activity scores ranged from 3 to 13 (8.0 +/- 2.7). Statistical analysis demonstrated a significant positive correlation (r = 0.34, p less than 0.005) between bone mineral density and back extensor strength. Bone mineral density was also positively correlated with the level of physical activity (r = 0.24, p less than 0.05). There was a significant positive correlation between back extensor strength and level of physical activity (r = 0.37, p less than 0.005). The data suggest that levels of physical activity and back muscle strength may be contributors to the bone mineral density of vertebral bodies.

Aged↗
PubMed1999

Prediction of maximal back muscle strength from indices of body mass and fat-free body mass.

OBJECTIVES: The purpose of this study was to examine, in healthy volunteers, the relationship between back extensor muscle strength and body size. METHODS: The maximal voluntary isometric back extensor strength of 456 volunteers, aged 18-42 yr and with no history of low back pain, was measured in a standing, slightly flexed forward posture. This was then correlated with two indices of body size: body mass and fat-free body mass. RESULTS: Significant linear relationships were observed between back muscle strength and each of the two indices of body size. There was a gender difference in both the slope and the intercept of the regression equations describing the relationships. There was no independent influence of age within the range studied. CONCLUSION: It was possible to establish predictive equations for back extensor strength based on body size which could be used to quantify strength 'deficits', for instance in patients with low back pain, and to prescribe submaximal target forces for use in endurance training and testing.

Adult↗
PubMed1994

Electrically evoked myoelectric signals in back muscles: effect of side dominance.

This work had two goals, to study the effect of hand dominance on myoelectric signal variables and fatigue indexes in back muscles and to assess the repeatability of the estimates of such variables. Myoelectric manifestations of muscle fatigue were studied in the right and left longissimus dorsi muscles of five right-handed and five left-handed normal male subjects. Myoelectric signals (M waves), evoked by stimulation applied to a muscle's motor point, were detected with surface electrodes. Each test consisted of eliciting a tetanic contraction of 30 s duration with supramaximal stimulation at 25 Hz and was repeated five times on 5 different days for each subject. The mean and median frequencies of the resulting power spectra of the M waves were plotted vs. time, and fatigue indexes were obtained from the time course of these variables. Only two-thirds of the elicited contractions provided signals of sufficiently good quality to obtain reliable estimates of the mean and median frequencies. Criteria for acceptability are described. Analysis of variance and paired comparisons showed a statistically significant effect of side dominance on fatigue indexes in the right-handed subjects but not in the left-handed subjects. Normalized initial slope and other fatigue indexes based on spectral variables demonstrated myoelectric manifestations of fatigue that were greater on the dominant side. We surmise that the differences are related to the fiber type modifications associated with the unilateral usage of the upper limbs and the consequent activation of the nondominant side of the back.

Adult↗
PubMed1975

Local muscle blood flow and sustained contractions of human arm and back muscles.

The endurance during sustained contraction of elbow, flexors, elbow extensors, and back extensors was tested in 3 human subjects. The force level used was varied between ca. 15 and ca. 75% of maximal isometric strength (IS). The clearance of 133Xe from contracting muscles was registered during and after the endurance test. In this way it was possible to determine whether muscle blood flow (MBF) was increased or had stopped during the contraction. Experiments with artificial ischaemia of the upper arm together with MBF measurements showed that MBF was of no importance for continuing sustained contractions above a certain force level, which was 50,25, and 40% of IS for elbow flexors, elbow extensors and back extensors, respectively. However, the level, where longer lasting ( greater than 15 min) sustained contraction is possible is directly related to MBF. These levels were 22, 15, and 20% IS for elbow flexors, elbow extensors, and back extensors, respectively.

Adult↗
PubMed1987

Lumbar back muscle activity during walking with a leg inequality.

The influence of an artificial leg length discrepancy (= ALLD) on stride times, pelvic rotations and activity of the intrinsic lumbar back muscles (= ILBM) was investigated for 20 subjects. An ALLD was created by shoes with a raised sole. Walking with an ALLD produced an increase of the swing phase time and a decrease of the stance phase time for both feet. The influence of an ALLD on pelvic rotations in the sagittal and frontal plane and on ILBM-activity was small. Changes in pelvic rotations in the sagittal plane were too small to observe. The mean pelvic rotation angle in the frontal plane was changed 1.52 degrees when walking with an ALLD of 40 mm (6.9 degrees while standing with an ALLD of 40 mm with extended knees). Only small changes were found in activity time due to an ALLD (not in EMG-amplitude). The activity time of the ILBM around heel strike of the raised limb was increased and unilaterally shifted from toe off in the direction of heel strike with the raised limb.

Electromyography↗
PubMed1999

Reliability of EMG spectral parameters in repeated measurements of back muscle fatigue.

The change in median frequency of the power spectrum of the electromyographic (EMG) signal may be used as a measure of muscle fatigue. The reliability of the median frequency parameters was investigated for EMG-recording sites at L1 and L5 right and left on the erector spinae. The reliability of subjective fatigue ratings of the back muscles (Borg CR-10 scale) and of maximal trunk extension torque (MVC) was also investigated. Eleven subjects with healthy backs performed a 45-s isometric trunk extension at 80% of MVC twice a day, on three different days. Two-factor analysis of variance was made to obtain the different variances from which the standard error of measurement (SEM) and the intra class correlation coefficient (ICC) were calculated. The SEM within-day was somewhat lower than that between-days. Both were about the same at all four electrode sites. The 95% confidence interval for the studied variables was for the initial median frequency +/- 10 Hz, for the slope +/- 0.4-0.5%/s, for the MVC +/- 36 Nm and for the Borg ratings +/- 1.6. We conclude that, with the presently used method, changes or differences within these limits should be regarded as normal variability. The slope may be of limited value because of its large variability. Whether the low intraclass correlation coefficient for the EMG parameters in the presently studied test group implies a low potential in discriminating subjects with back pain can not be decisively concluded.

Adult↗
PubMed1988

Low back muscle activity and pelvic rotation during walking.

Gait variables, pelvic rotations in the frontal and sagittal plane and RA-EMG (rectified and averaged EMG) of the three columns of the intrinsic lumbar back muscles (= ILBM) were recorded simultaneously during 48 succeeding strides of 11 subjects on a treadmill. Bilateral activity is found in all parts of the ILBM during the double support phase. After right heel strike the right ILBM (and after left heel strike the left) show in most cases more activity than the contralateral ILBM. This is especially so in the intermediate and lateral columns, which consist mainly of the longissimus thoracis and the iliocostalis lumborum muscle and less so in the medial column, made up mainly by the multifidus and spinalis muscle. This difference is probably due to the difference in moment arm for the two directions. Pelvic rotations are described, but no evident relationships between pelvic rotations in the different planes and ILBM-activity could be seen, probably because the changes in the position of the torso are of more importance.

Adult↗
PubMed1982

[Analyses on the fiber compositions of the lumbar back muscles in mammals].

Monkeys, being close to the human, have a lot of opportunities to sustain the lumbar spine in the extended or upright position. So it is interesting to compare the histochemical profiles of the fiber types in the lumbar back muscles of monkey with those of the other tetrapod animals. An attempt was made to analyze the muscle fiber compositions of the whole epaxial muscles from 32 mice, 28 rats, 18 cats, 27 dogs and 8 monkeys, using the Sudan black B staining. In the present study, the epaxial muscular systems in cross section were divided into three compartments in mouse and rat: transversospinalis (TS), medial component of longissimus (McL) and lateral longissimus (LL), or into four compartments in cat, dog and monkey: TS, McL, longissimus (LG) and iliocostalis (IC). Fiber counting was undertaken by the light microscope widely through the each compartment. Results were as follows. The mean percentages of the white fibers progressively increased towards the laterally located muscle compartments of the epaxial muscles in every animal except monkey. As the most noteworthy difference from the other animals, a large dark area was found in the monkey longissimus muscle. This area was composed solely or predominantly (85-90%) of "non white fibers" which could not be referred to whether the red or the intermediate fiber. Consequently, it caused marked decrease of the white fibers, whereas a mosaic pattern of fibers was presented in the whole LG compartments of the other animals. The "non white fibers", which seem to take part in the tonic movement of the muscle, appear to be the resultant differentiation as an adaptation for keeping the vertebral column in the upright position in monkey. Concerning the sizes of the red fibers in the epaxial muscles and the m. rectus abdominis (RA), those of the RA were markedly smaller than those of the epaxial muscles in mouse, rat, cat and dog except monkey. But the size of the red fibers in the RA of monkey was as large as that in the epaxial muscle of monkey. From these findings, it is likely to understand that the epaxial muscle in monkey, in contrast to the other tetrapod animals, functions antagonistically with the rectus abdominis muscle. The total numbers and the sizes of the muscle fibers in the RA and the epaxial muscles for both sexes of the mouse and rat during growth were also investigated.

Age Factors↗
PubMed1987

Fibre types in human lumbar back muscles.

The distribution of histochemically identified muscle fibre types was studied in biopsy samples from the two main muscles in the lumbar region of the human erector spinae, the multifidus and the longissimus, in 16 healthy subjects (nine males and seven females, age 20-30 years). Muscle fibres were classified as types I, IIA, IIB or IIC on the basis of the pH lability of their myofibrillar ATPases. There were no differences between the multifidus and the longissimus muscles in the relative occurrence of type I (62 vs. 57%), type IIA (20 vs. 22%) or type IIB fibres (18 vs. 22%), or in the absolute size of fibres (range of mean least diameters 58-66 micron). The oxidative potential (NADH-diaphorase staining intensity) was high in type I and low in type II fibres, irrespective of subgroups, in both muscles. In the females, the type I fibres occupied a relatively larger area (70-75 vs. 54-58% for the males) although the relative number of type I fibres was the same in both sexes. This was due to smaller type II fibres in the females resulting in higher type I/type II area ratios (1.70-1.90 vs. 0.88-0.92 for males). This suggests a difference in functional capacity of lumbar back muscles between males and females. On the other hand, the similarity in histochemical fibre-type distribution between the multifidus and the longissimus muscles does not give support for a functional differentiation between these two anatomically different parts of the lumbar erector spinae in man.

Adenosine Triphosphatases↗
PubMed2005

Back muscle activation pattern and spectrum in defined load situations.

For the prevention and rehabilitation of low back pain the understanding muscle function in the low back region is essential. Important aspects of function include the muscle activation patterns and muscle fatigue. In the low back region m. erector spinae plays a critical role. The different parts of this muscle complex differ considerably in function. Following the concept of Bergmark [A. Bergmark, Stability of the lumbar spine, Acta Orthop. Scand. 60 (1989) 1-54] trunk muscles can be divided in two subsystems, the global-mobilizing-system and the local-stabilizing-system. At present the multifidus muscles are assigned to the local whereas the longissimus and iliocostalis muscles are assigned to the global system. From results of the four parts of our investigation, it can be shown that essential information about muscle function can be obtained by spectral and intra- as well as inter-muscular surface EMG parameters. Obtained data demonstrated functional transitions between the local and global system of trunk muscles for the multifidus muscle.

Journal Article↗
PubMed1989

Lower back muscle forces in pushing and pulling.

In the investigation of lower back stress, the muscle forces of the erector spinae and the rectus abdominis are often calculated using the two-dimensional biomechanical model. These muscle forces are used to estimate the compressive forces at L5/S1 disc. This paper presents a study of the muscle forces predicted by a two-dimensional biomechanical model during pushing and pulling and myoelectric activity from the corresponding muscles. The goal was to investigate whether a simple two muscle torso model would reasonably estimate the muscle actions in pushing and pulling tasks. Six subjects participated in the experiment. EMG (rms) value was used as an indicator of muscle forces. The results show high correlation between the predicted muscle forces and the measured root-mean-square EMG values in trunk pushing and pulling (r2 = 0.93) and hand pushing and pulling (r2 = 0.96) in an erect posture with hips braced but low in hand pushing and pulling using a free posture (r2 = 0.37).

Abdominal Muscles↗