Long-term electromyographic activity in upper trapezius and low back muscles of women with moderate physical activity.

The habitual activity patterns of trapezius and postural back muscles (multifidus, iliocostalis, longissimus) of 23 female subjects with moderate physical activity were studied. Bilateral surface electromyographic (sEMG) recordings from start of work until bedtime were analyzed. The activity level was calibrated as percentage of root mean square-detected muscle activity at maximal voluntary contraction (EMG(max)). Sixty-six previous trapezius recordings of women with moderate physical activity were included in some analyses to pursue the full range of variation in trapezius activity. Twenty-six of these were recorded twice, separated by 16-28 mo. Median activity level and duration of periods with sEMG activity of <0.5% EMG(max) ("rest time"; only trapezius) and exceeding 2 ("burst time"), 10, 30, and 50% EMG(max) was determined. The trapezius median activity level ranged from 0.6 to 8.8% EMG(max), burst time from 9 to 84%, and rest time from 2 to 84%. The activity patterns of the back muscles showed similar large interindividual variation. Repeated trapezius recordings of the same subject showed high consistency; intraclass correlation coefficients ranged from 0.62 to 0.79 for different sEMG variables. Periods with high sEMG amplitude were of short duration; 7% of the trapezius recordings did not present time intervals (0.2-s duration) above 50% EMG(max). The activity patterns of the postural muscles, despite large interindividual variability, were distinctly different from activity patterns of upper and lower limb muscles reported by others (e.g., mean burst time 40-50 vs. 10-20%). We conclude that postural trunk muscles show idiosyncratic activity patterns with large interindividual variation. High-threshold motor units are activated to a very minor extent.     

EMG scanning in the diagnosis of chronic pain

A surface EMG diagnostic protocol was developed to assess the neuromuscular/postural contributions to pain states. The EMG activity of the right and left aspects of 11 muscle groups were monitored while the patient was in the sitting and standing positions. The diagnostic protocol was evaluated by comparing the patterns of EMG activity in four diagnostic groups: headache only, neck/shoulder/upper back pain only, low back pain only, and mixed pain states. The results suggest that (1) bilateral levels of EMG activity in the frontalis and masseter groups are of primary importance for the headache patients, (2) the discrepancy between the right and left EMG activity in the lumbar and cervical paraspinal muscle groups are of primary importance for low back pain patients, (3) position (sit/stand) may provide important diagnostic information, and (4) the data appear to support the notion of a postural disturbance as a contributing factor in low back pain.     

Muscle synergies during shifts of the center of pressure by standing persons: identification of muscle modes

When a standing person performs a movement such that the center of gravity shifts, the activity of postural muscles adjusts to keep the balance. We assume that such adjustments are controlled using a small set of central variables, while each variable induces changes in the activity of a subgroup of postural muscles. The purpose of this study has been to identify such muscle groups (muscle modes or M-modes) and compare them across tasks and subjects. Four tasks required the subjects to release a load from extended arms leading to a center of pressure (COP) shift prior to the load release. The fifth task required an explicit COP shift by voluntary sway. Electromyographic activity of 11 postural muscles on one side of the body was integrated over a 100-ms interval corresponding to the early stage of the COP shift, and this integrated EMG activity was subjected to a principal component (PC) analysis across multiple repetitions of each task. Three PCs were identified and associated with a push-back M-mode, a push-forward M-mode, and a mixed M-mode. Cluster analysis of the PC vectors across tasks and across subjects confirmed the existence of distinctive push-forward and push-back muscle groups. PC vectors were also compared across tasks and across subjects using cosines as a measure of colinearity between pairs of vectors. In general, M-modes were similar across both tasks and subjects. We conclude that shifts of the COP, whether implicit or explicit, are controlled using a small set of central variables associated with changes in the activity of robust subsets of postural muscles. These results can be used for future analysis of muscle synergies associated with postural tasks.     

EMG muscle scanning: Stability of hand-held surface electrodes

Electromyographic (EMG) muscle scanning measures 2-second samples of integrated muscle action potentials from individual neck and back muscles using a hand-held scanner with post-style surface electrodes separated by a fixed distance. This scanning technique is widely used to expeditiously assess muscle activity in the diagnosis of musculoskeletal disorders. In order to determine if the 2-second sample is sufficiently representative of electrical activity at a specific muscle site, the stability of the signal received by the hand-held scanner was measured bilaterally at six neck and back muscle sites over 40 seconds (20 2-second integration periods) in five seated subjects. Taking the overall average EMG activity as the true value, the mean number of 2-second integration periods required to achieve <5% standard error was calculated to be 1.47 for the 60 muscles tested. Only three sites required more than five integration periods. The validity of EMG scanning as a diagnostic tool is enhanced by longer integration periods     

Comments on the reliability of muscle activity comparisons in EMG biofeedback research with back pain patients

The underlying assumption in comparing muscle activity levels in back pain research is the reliability of the documented biological record. Surface-recorded EMG data are often used as objective indicators in treatment outcome studies. The present paper questions the reliability of this somatic measure. Three sources of error variance that interfere with the reliability of the recorded biological signal are discussed: movement of the body, replacement of electrodes, and electronic equipment instability. It is argued that surface-recorded EMG activities of the back are unreliable and unsuited for comparing the efficacy of a back pain treatment program.The author wishes to thank Dr. A. W. MacLean for his critical comments and E. J. Bradley for her editorial suggestions on an earlier draft of this paper.     

Evaluation of Novel EMG Biofeedback for Postural Correction During Computer Use

Postural correction is an effective rehabilitation technique used to treat chronic neck and shoulder pain, and is aimed toward reducing the load on the surrounding muscles by adopting a neutral posture. The objective of this investigation was to evaluate the effectiveness of real-time high-density surface EMG (HDsEMG) biofeedback for postural correction during typing. Twenty healthy participants performed a typing task with two forms of postural feedback: (1) verbal postural coaching and (2) verbal postural coaching plus HDsEMG biofeedback. The interface used activity from two HDsEMG arrays placed over the trapezius designed to shift trapezius muscle activity inferiorly. The center of gravity across both arrays was used to quantify the spatial distribution of trapezius activity. Planar angles taken from upper extremity reflective markers quantified cervicoscapular posture. During the biofeedback condition, trapezius muscle activity was located 12.74 ± 3.73 mm more inferior, the scapula was 2.58 ± 1.18° more adducted and 0.23 ± 0.24° more depressed in comparison to verbal postural coaching alone. The results demonstrate the short-term effectiveness of a real-time HDsEMG biofeedback intervention to achieve postural correction, and may be more effective at creating an inferior shift in trapezius muscle activity in comparison to verbal postural coaching alone.     

The influence of initial posture on the sit-to-stand movement

Head movements, ground reaction forces and electromyographic activity of selected muscles were recorded simultaneously from two subjects as they performed the sit-to-stand manouevre under a variety of conditions. The influence of initial leg posture on the magnitude of the various parameters under investigation was examined first. A preferred initial leg posture resulted in smaller magnitudes of head movement and ground reaction forces. EMG activity in some muscles, trapezius and erector spinae, decreased, while in others, quadriceps and hamstrings, it increased in the preferred leg posture. The decreases seen correlate with reductions in head movement observed. The effect of inhibiting habitual postural adjustments of the head and neck, by comparing "free" and "guided" movements was also examined. In guided movements there are significant reductions in head movement, ground reaction forces and EMG activity in trapezius, sternomastoid and erector spinae. It would appear that both initial leg posture and the abolition of habitual postural adjustment have a profound influence on the efficiency of the sit-to-stand manouevre. This preliminary study high-lights the practical importance of head posture in the diagnosis and treatment of movement disorders, as well as in movement education.     

Evolutionary relationships of the carbamoylphosphate synthetase genes

Carbamoylphosphate is a common intermediate in the metabolic pathways leading to the biosynthesis of arginine and pyrimidines. The amino acid sequences of all available proteins that catalyze the formation of carbamoylphosphate were retrieved from Genbank and aligned to estimate their mutual phylogenetic relations. In gram-negative bacteria carbamoylphosphate is synthesized by a two-subunit enzyme with glutamiriase and carbamoylphosphate synthetase (CPS) activity, respectively. In gram-positive bacteria and lower eukaryotes this two-subunit CPS has become dedicated to arginine biosynthesis, while in higher eukaryotes the two subunits fused and subsequently lost the glutaminase activity. The CPS dedicated to pyrimidine synthesis is part of a multifunctional enzyme (CPS II), encoding in addition dihydroorotase and aspartate transcarbamoylase. Evidence is presented to strengthen the hypothesis that the two kinas subdomains of all CPS isozymes arose from a duplication of an ancestral gene in the progenote. A further duplication of the entire CPS gene occurred after the divergence of the plants and before the divergence of the fungi from the eukaryotec root, generating the two isoenzymes involved in either the synthesis of arginine or that of pyrimidines. The mutation rate was found to be five- to tenfold higher after the duplication than before, probably reflecting optimization of the enzymes for their newly acquired specialized function. We hypothesize that this duplication arose from a need for metabolic channeling for pyrimidine biosynthesis as it was accompanied by the tagging of the CPS gene with the genes for dihydroorotase and aspartate transcarbamoylase, and as the duplication occurred independently also in gram-positive bacteria. Analysis of the exon-intron organization of the two kinase subdomains in CPS I and II suggests that ancient exons may have comprised approx. 19 amino acids, in accordance with the prediction of the intron-early theory. Correspondence to: M.J.B. van den Hoff     

Postural responses to vibrostimulation of the neck muscle proprioceptors in man

Postural responses to vibrostimulation (50–100 Hz, 0.5 mm, 4–8 sec) of muscles of the back surface of the neck were studied in healthy subjects. In the sitting position, vibrostimulation evoked local displacements (backward head deflection), but global postural responses (forward inclination of the whole body) developed in the standing position. The amplitude of the evoked body inclination was dependent upon the site of the vibrostimuli application along the vertebral column. Asymmetrical application of vibrostimuli to the muscles of the right or left neck side was accompanied by development of a lateral component in the postural response. Changes in the spatial orientation of the head led to the changes in postural response direction: head turning to the right resulted in right-side body deviation during vibration, and vice versa. Illusions of head bend caused by habituation to its static turning were accompanied by precisely the same changes in the direction of body deviation. It is assumed that neck-evoked motor events are mediated via central mechanisms that are involved in perception of the head and body position in space.Translated from Neirofiziologiya, Vol. 25, No. 2, pp. 101–108, March–April, 1993.     

Postural maintenance during movement: Simulations of a two joint model

Voluntary movements of the upper body are accompanied by anticipatory postural adjustments to the lower body in a standing subject. The long-standing hypothesis is that these anticipatory adjustments serve to counteract the perturbation to the body's center of gravity caused by the voluntary arm movement. This paper presents model simulations investigating the possible roles of anticipatory postural activity that accompanies a rapid, upward arm swing. The model encorporates two (idealized) antagonistic muscle pairs controlling the movements of a double-joint system, with a shoulder joint between the arm and stiff body links, and an ankle joint between the stiff body-leg segment and the ground. Each muscle is represented by a nonlinear viscoelastic element and also includes proprioceptive feedback. Four inputs to the model define the motor control signals for muscle force generation in both the arm and the postural muscle pairs. The neurological component of the model describes consequences of alternate strategies for cocontractions, stretch reflex activity, and anticipatory and synchronous postural activities (or combinations thereof). Simulations with this model show that: (1) none of the postural maintenance schemes considered in these simulations (including varying anticipation) could suppress the initial backward thrust on the body link; (2) the more important destabilizing perturbation is a subsequent forward sway that, left uncountered by postural activity, would eventually leave the body to fall flat on its face; and (3) anticipatory silencing of the postural extensor followed by a brief period of extensor activation (descending control) and synchronous reflex activity (feedback control) appears to be the most likely postural stabilizing strategy that inhibits the continuous forward sway and is consistent with the experimental evidence.     

Histochemical evidence for granulosa steroids in follicle maturation in the African catfish,Clarias lazera

Summary The effects of carp pituitary suspension (CPS) and 11-desoxycorticosterone-acetate (DOCA) on 3-hydroxysteroid dehydrogenase (3-HSD) and glucose-6-phosphate dehydrogenase (G6PD) activity in the ovary of Clarias lazera are described. Strong 3-HSD and G6PD activities are localized in the stroma, of both control and treated fish. A single CPS injection stimulates 3-HSD activity in the granulosa of postvitellogenic, maturing and postovulatory follicles, but DOCA has no such effect on the postvitellogenic and maturing follicles, and only stimulates a weak response in the postovulatory ones.     

A two compartment model of the stepping generator: Analysis of the roles of a stage-setter and a rhythm generator

Recent studies on locomotion of the mesencephalic cat demonstrated that activation of the spinal stepping generator and the postural control system are dependent phenomena (Mori et al., 1978, 1980). This has motivated the construction of a new model of the stepping generator to account for interactions with the postural control system. The present model consists of two main compartments, the rhythm generator and the stage-setter. The rhythm generator generates rhythmic bursting discharges of extensor and flexor alpha motoneurons. The function of the stage-setter is to set and reset the excitability of extensor alpha motoneuron to a number of desired levels. This study analyzes interactions in this model between rhythm generating and postural control system. By adding a concept of stage-setting to the rhythm generator model, we succeed in simulating a variety of locomotor patterns observed in the mesencephalic cat, including stepping automatism (Mori et al., 1979).     

Postural taping applied to the low back influences kinematics and EMG activity during patient transfer in physical therapists with chronic low back pain

We examined the influence of the application of postural taping on the kinematics of the lumbo–pelvic–hip complex, electromyographic (EMG) activity of back extensor muscles, and the rating of perceived exertion (RPE) in the low back during patient transfer. In total, 19 male physical therapists with chronic low back pain performed patient transfers with and without the application of postural taping on the low back. The kinematics of the lumbo–pelvic–hip complex and EMG activity of the erector spinae were recorded using a synchronized 3-D motion capture system and surface EMG. RPE was measured using Borg’s CR-10 scale. Differences in kinematic data, EMG activity, and RPE between the two conditions were analyzed using a paired t-test. Peak angle and range of motion (ROM) of lumbar flexion, EMG activity of the erector spinae, and RPE decreased significantly, while peak angle and ROM of pelvic anterior tilt and hip flexion increased significantly during patient transfer under the postural taping condition versus no taping (p < 0.05). These findings suggest that postural taping can change back extensor muscle activity and RPE as well as the kinematics of the lumbo–pelvic–hip complex in physical therapists with chronic low back pain during patient transfer.     

Specific and nonspecific effects of EMG biofeedback

This study investigated the effects of performance feedback and EMG biofeedback on perceptions of the self (i.e., self-esteem, self-control, self-efficacy, and locus of control) as well as on a self-control behavior (study skills) the subjects performed outside the laboratory. Forty-seven college students were randomly assigned to one of four groups in a 2(high and low success feedback) × 2(true and false EMG biofeedback) factorial experiment with repeated measures. All of the participants received four sessions of EMG biofeedback, and later they were asked to self-monitor their study habits for 2 weeks. Results showed that the self-esteem measure and perceptions of study skills improvement were differentially affected by success feedback but unrelated to the true or false EMG manipulation. Shifts toward an internal locus of control and perceptions of improved self-control were also noted, but they were independent of the subjects' group membership. Implication of the results are briefly discussed.     

The effect of surgical floor mats in prolonged standing: an EMG study of the lumbar paraspinal and anterior tibialis muscles

The purpose of this study was to determine whether or not surgical floor mats affect low back and leg muscle activity during prolonged standing. The EMG activity was measured continuously using surface electrodes on the paraspinal muscles of the low back and on the anterior tibialis muscles; the subjects were normal and stood on two different surfaces. Six male subjects were each instructed to stand for two hours on a specially designed surgical floor mat and then, on a separate day, to stand for two hours on a linoleum-covered concrete surface. Six other subjects carried out the same procedure, but stood on the linoleum first. There was no difference in EMG activity obtained from the anterior tibialis muscles and paraspinal muscles of the low back when the subjects stood on the surgical mat, as compared with the linoleum-covered concrete.     

Selective activation of the latissimus dorsi and the inferior fibers of trapezius at various shoulder angles during isometric pull-down exertion

The aim of this study was to determine the effect of isometric pull down exercise on muscle activity with shoulder elevation angles of 60°, 90°, and 120° and sagittal, scapular, and frontal movement planes, by electromyography (EMG) of the latissimus dorsi, inferior fibers of trapezius, and latissimus dorsi/inferior fibers of trapezius activity ratio. Fourteen men performed nine conditions of isometric pull down exercise (three conditions of shoulder elevation × three conditions of movement planes). Surface EMG was used to collect data from the latissimus dorsi and inferior fibers of trapezius during exercise. Two-way repeated analysis of variance with two within-subject factors (shoulder elevation angles and planes of movement) was used to determine the significance of the latissimus dorsi and inferior fibers of trapezius activity and latissimus dorsi/inferior fibers of trapezius activity ratio. The latissimus dorsi activity and ratio between the latissimus dorsi and the inferior fibers of trapezius were significantly decreased as shoulder elevation angle increased from 60° to 120°. The inferior fibers of trapezius activity was significantly increased with shoulder elevation angle. The EMG activity and the ratios were not affected by changes in movement planes. This study suggests that selective activation of the latissimus dorsi is accomplished with a low shoulder elevation angle, while the inferior fibers of the trapezius are activated with high shoulder elevation angles.     

EMG biofeedback of the abductor pollicis brevis in piano performance

The aim of the present study was to apply EMG biofeedback as an auxiliary to piano teaching techniques. We studied the changes in integrated electromyographic activity, using the abductor pollicis brevis functioning as an agonist during the teaching of identical selective movements of piano playing in two groups, one with EMG biofeedback and the other following traditional method of instruction. The analysis of variance revealed an increase in the peak amplitude and the relaxation rate values for the biofeedback group. These results have implications for the application of piano playing techniques and reveal EMG biofeedback as an aid in the teaching of thumb attack with the abductor pollicis brevis as agonist.We are grateful for the valuable assistance of Dr. Jaime Vila (Professor of Therapy and Behavioral Modification, Faculty of Psychology, Granada), the cooperation of students at the Juventudes Musicales Music School, Santa Fe and at the Victoria Eugenia Conservatoire, (Granada), the Statistical Analysis Centre of University of Filosofia y Letras de Granada; Professor Enrique Garcia Fernandez-Abasal (Complutense University) for the design of the interface and software.     

Anticipatory postural adjustments to arm movement reveal complex control of paraspinal muscles in the thorax

Anatomical and empirical data suggest that deep and superficial muscles may have different functions for thoracic spine control. This study investigated thoracic paraspinal muscle activity during anticipatory postural adjustments associated with arm movement. Electromyographic (EMG) recordings were made from the right deep (multifidus/rotatores) and superficial (longissimus) muscles at T5, T8, and T11 levels using fine-wire electrodes. Ten healthy participants performed fast unilateral and bilateral flexion and extension arm movements in response to a light. EMG amplitude was measured during 25 ms epochs for 150 ms before and 400 ms after deltoid EMG onset. During arm flexion movements, multifidus and longissimus had two bursts of activity, one burst prior to deltoid and a late burst. With arm extension both muscles were active in a single burst after deltoid onset. There was differential activity with respect to direction of trunk rotation induced by arm movement. Right longissimus was most active with left arm movements and right multifidus was most active with right arm movements. All levels of the thorax responded similarly. We suggest that although thoracic multifidus and longissimus function similarly to control sagittal plane perturbations, these muscles are differentially active with rotational forces on the trunk.     

Finger pulse amplitude and frontalis EMG biofeedback effects of single- and two-system training

The relationship between finger pulse amplitude (PA) and frontalis EMG was studied first by looking at general physiological changes accompanying successful bidirectional PA control. Seven successful subjects were then asked to produce two patterns of PA and EMG (PAincEMGdec and PAdecEMGdec) while receiving both PA and frontalis EMG biofeedback. Results indicate subjects can easily produce the differentiation pattern of PAdecEMGdec but cannot produce the integration pattern of PAincEMGdec. These rather paradoxical results may indicate subjects were using an attentional rather than arousal strategy for controlling PA and have implications for the use of peripheral vasomotor training as a general relaxation technique.     

Force-length, torque-angle and EMG-joint angle relationships of the human in vivo biceps brachii

The relationships of EMG and muscle force with elbow joint angle were investigated for muscle modelling purposes. Eight subjects had their arms fixed in an isometric elbow jig where the biceps brachii was electrically stimulated (30 Hz) and also in maximum voluntary contraction (MVC). Biceps EMG and elbow torque transduced at the wrist were recorded at 0.175 rad intervals through 1.75 rad of elbow extension. The results revealed that while the torque-length relationship displayed the classic inverted U pattern in both evoked and MVC conditions, the force-length relationship displayed a monotonically increasing pattern. Analyses of variance of the EMG data showed that there were no significant changes in the EMG amplitudes for the different joint angles during evoked or voluntary contractions. The result also showed that electrical stimulation can effectively isolated the torque-angle and force-length relationships of the biceps brachii and that the myoelectric signal during isometric contraction is uniform regardless of the length of the muscle or the joint angle.