Reference Contraction Research Articles

Precision of measurements of physical workload during standardised manual handling. Part I: Surface electromyography of m. trapezius, m. infraspinatus and the forearm extensors

Though surface electromyography (EMG) has been widely used in studies of occupational exposure, its precision in terms of the variance between-days and between-subjects has seldom been evaluated. This study aimed at such an evaluation. Six women performed three different work tasks: ‘materials picking’, ‘light assembly’, and ‘heavy assembly’, repeated on 3 different days. EMG was recorded from m. trapezius, m. infraspinatus and the forearm extensors. Normalisation was made to a maximal (MVE), and a submaximal (RVE), reference contraction. Variance components between days (within subjects) and between subjects were derived for the 10th, 50th and 90th percentiles, as well as for muscular rest parameters. For the task ‘heavy assembly’, the coefficient of variation between days (CV BD) was 8% for m. trapezius (right side, 50th percentile, MVE normalised values). Larger variabilities were found for m. infraspinatus (CV BD 15%), and the forearm extensors (CV BD 33%). Between-subjects variability (CV BS) was greater, 16% for m. trapezius and 57% for m. infraspinatus, 29% for the forearm extensors. RVE normalisation resulted in larger CV BD, while reducing CV BS. The between-days and between-subjects variability may be used to optimise sampling strategy, and to assess the bias in epidemiological studies. The bias caused by measurement procedures per se is acceptable.

Effect of histamine on lung contractile elements in growing cattle.

To determine the effect of histamine on the contractile elements of the respiratory tract in neonatal calves and young adult cattle. Samples of trachealis muscle, bronchi, and intrapulmonary arteries and veins dissected from the respiratory tracts of healthy bovids (2 to 8 days and 16 to 20 months old). Histamine cumulative concentration-effect curves (10(-6) to 10(-3) M) were constructed in duplicate smooth muscle samples mounted in organ baths. Contractile responses to histamine were compared with reference contractions elicited by methacholine (10(-5) M) for airways or KCl (127 mM) for vessels. In young adult cattle, trachealis muscle had a substantial contractile response to histamine (84% of methacholine-induced contraction), whereas bronchi reacted slightly (15 and 20% for large and small bronchi, respectively). Although contractile responses to KCl were comparable in arteries and veins, histamine-induced contractions were greater for intrapulmonary veins than for arteries (202 vs 48% of KCl-induced contraction). In neonatal calves, histamine-induced contraction of veins also exceeded that of arteries (230 vs 54% of KCl-induced contraction); however, unlike in young adult cattle, histamine produced notable contraction of large and small bronchi (48 and 60% of methacholine-induced contraction, respectively). Compared with intrapulmonary arteries, intrapulmonary veins have greater contractile responses to histamine in neonatal and young adult cattle. Data suggest loss of histamine responsiveness in bronchial smooth muscle as neonatal calves grow to young adults. Venodilation may be useful in treatment of lung edema in cattle.

Force depression following muscle shortening of voluntarily activated and electrically stimulated human adductor pollicis.

The purpose of this study was to investigate steady-state force depression following active muscle shortening in human adductor pollicis during voluntary and electrically induced contractions. Subjects (n = 12; age 28 +/- 5 years; 7 males and 5 females) performed isometric reference contractions and isometric-shortening-isometric contractions, using maximal voluntary effort and near-maximal electrical stimulation. Force depression was assessed by comparing the steady-state isometric forces produced following active muscle shortening with the purely isometric reference forces obtained at the corresponding muscle length. In order to test for effects of the shortening conditions on the steady-state force depression, the amplitude and speed of shortening were changed systematically in a random order but balanced design. Thumb adduction force and carpometacarpal joint angle were continuously measured using a custom-designed dynamometer. During voluntary contractions, muscle activation was recorded using electromyography and the superimposed twitch technique. During electrically induced contractions, muscle stiffness was assessed using a quick-stretch method. Force depression during voluntary contractions, with a constant level of muscle activation, was similar to that obtained during electrically induced contractions. Force depression increased with increasing amplitudes of shortening (9.9 +/- 1.6%, 15.6 +/- 2.4% and 22.4 +/- 2.4% for 10, 20 and 30 deg of shortening, respectively) and decreased with increasing speeds of shortening (27.1 +/- 2.5%, 19.3 +/- 1.6% and 15.6 +/- 1.8% for 20, 60 and 300 deg s(-1) of shortening, respectively), regardless of the activation method. Muscle stiffness was significantly lower in the force-depressed state (5.9 +/- 0.2 N deg(-1)) compared with that of the isometric reference contractions (7.2 +/- 0.3 N deg(-1)), and decreased with increasing force depression (6.6 +/- 0.5, 6.0 +/- 0.5 and 5.3 +/- 0.4 N deg(-1) for the 10, 20 and 30 deg of shortening test contractions, respectively). Force depression appeared to be fully established at the end of the shortening phase. The results of this study suggest that steady-state force depression for voluntary movements is similar to that observed using electrical stimulation. Furthermore, it appears that force depression is established at the end of the shortening phase and is associated with a reduction in muscle stiffness and thus, presumably, a decrease in the proportion of attached cross-bridges.

Influence of the subcutaneous fat layer, as measured by ultrasound, skinfold calipers and BMI, on the EMG amplitude.

Surface electromyography (sEMG) is an important tool to estimate muscular activity at work. There is, however, a great inter-individual variation, even in carefully standardized work tasks. The sEMG signal is attenuated in the subcutaneous tissues, differently for each subject, which requires normalization. This is commonly made in relation to a reference contraction, which by itself, however, introduces a variance. A normalization method that is independent of individual motivation, motor control and pain inhibition would be desirable. The aim of the study was to explore the influence of the subcutaneous tissue thickness on sEMG amplitude. Ultrasound measurements of the muscle to skin surface distance were made bilaterally over the trapezius muscle in 12 females. Skinfold caliper measurements from these sites, as well as from four other sites, were made, body mass index (BMI) was recorded, and sEMG was recorded at maximal and submaximal contractions. The muscle-electrode distance, as measured by ultrasound, explained 33% and 31% (on the dominant and non-dominant sides respectively) of the variance of the sEMG activity at a standardized submaximal contraction (average between the sides, 46%); for maximal contractions the explained variance was 21%. Trapezius skinfold measurements showed poor correlations with sEMG. Instead, the mean of skinfold measurements from other sites explained as much as 68% (submaximal contraction). The corresponding figure for BMI was 67%. In conclusion, skinfold thickness explains a major part of the inter-individual variance in sEMG amplitude, and normalization to this measure is a possibility worth further evaluation.

The impact of working technique on physical loads—an exposure profile among newspaper editors

The aim of this study was to investigate the possible associations between working technique, sex, symptoms and level of physical load in VDU-work. A study group of 32 employees in the editing department of a daily newspaper answered a questionnaire, about physical working conditions and symptoms from the neck and the upper extremities. Muscular load, wrist positions and computer mouse forces were measured. Working technique was assessed from an observation protocol for computer work. In addition ratings of perceived exertion and overall comfort were collected. The results showed that subjects classified as having a good working technique worked with less muscular load in the forearm (extensor carpi ulnaris p=0.03) and in the trapezius muscle on the mouse operating side (p=0.02) compared to subjects classified as having a poor working technique. Moreover there were no differences in gap frequency (number of episodes when muscle activity is below 2.5% of a reference contraction) or muscular rest (total duration of gaps) between the two working technique groups. Women in this study used more force (mean force p=0.006, peak force p=0.02) expressed as % MVC than the men when operating the computer mouse. No major differences were shown in muscular load, wrist postures, perceived exertion or perceived comfort between men and women or between cases and symptom free subjects. In conclusion a good working technique was associated with reduced muscular load in the forearm muscles and in the trapezius muscle on the mouse operating side. Moreover women used more force (mean force and peak force) than men when operating the click button (left button) of the computer mouse.

Effects of experimentally induced mental and physical stress on motor unit recruitment in the trapezius muscle

Mental stress may induce muscle tension and it is thought to contribute to the development of musculoskeletal disorders. Prolonged activity of a muscle's motor units (the smallest functional units) having low activation thresholds, may cause metabolic disturbances, degenerative processes and pain. The present experiment was aimed at investigating if the same motor units are activated by mental stress as by physical demands. Seventeen participants were exposed to mental stress tests (mental arithmetic, Stroop color word) and physical demands (standardized reference contraction, force ramp contraction) in the laboratory. In addition, they were exposed to the cold pressor test. Bipolar intramuscular electromyographic (EMG) activity was measured in the trapezius muscle, which covers the upper part of the back, the neck and the shoulder, and an automatic classification programme was used to separate the contributions of the individual motor units in the compex EMG signal. Overall muscle activity was measured by bipolar surface EMG and heart rate was recorded as an indicator of stress. The mental stress induced significant increases in muscle activity ( p < .05) and in heart rate ( p < .05). In 12 out of 14 participants, one or more motor units were found to be active in mentally as well as in physically induced muscle contraction. The results indicate that mentally induced stress may contribute to keeping low threshold motor units active, even in the absence of physical demands. Considering the health risks of prolonged motor unit activity, it was concluded that lack of mental rest is an important risk factor for the development of muscular pain.

Estimation of cat medial gastrocnemius fascicle lengths during dynamic contractions

In typical muscle models, it is often assumed that the contractile element (fascicle) length depends exclusively on the instantaneous muscle–tendon length and the instantaneous muscle force. In order to test whether the instantaneous fascicle length during dynamic contractions can be predicted from muscle–tendon length and force, fascicle lengths, muscle–tendon lengths, and muscle forces were directly measured in cat medial gastrocnemii during isometric and dynamic contractions. Two theoretical muscle models were developed: model A was based on force–time data obtained during the activation phase and model D on force–time data obtained during the deactivation phase of isometric contractions. To test the models, instantaneous fascicle lengths were predicted from muscle–tendon lengths and forces during dynamic contractions that simulated cat locomotion for speeds ranging from 0.4 to 1.6 m/s. The theoretically predicted fascicle lengths were compared with the experimentally measured fascicle lengths. It was found that fascicle lengths were not uniquely associated with muscle–tendon lengths and forces; that is, for a given muscle–tendon length and force, fascicle lengths varied depending on the contractile history. Consequently, models A and D differed in fascicle length predictions; model D (maximum average error=8.5%) was considerably better than model A (maximum average error=22.3%). We conclude from this study that it is not possible to predict the exact fascicle lengths from muscle–tendon lengths and forces alone, however, adequate predictions seem possible based on such a model. The relationship between fascicle length and muscle force and muscle–tendon length is complex and highly non-linear, thus, it appears unlikely that accurate fascicle length predictions can be made without some reference contractions in which fascicle length, muscle–tendon length, and force are measured simultaneously.

Differing Effects of Inotropic Agents on Length Change Deactivation of Isolated Rat Myocardium

BackgroundA rapid change in length of cardiac muscle during isometric contraction is followed by developed force that is less than appropriate for the new length because of deactivation of the...

Upper trapezius muscle mechanomyographic and electromyographic activity in humans during low force fatiguing and non-fatiguing contractions

The purposes of this study were firstly to compare and investigate localised fatigue in the upper trapezius muscle in various arm positions as assessed by mechanomyographic (MMG) and surface electromyographic (EMG) signals and secondly to study the effects of different normalisation methods on MMG and EMG signals during non-fatiguing and fatiguing low level isometric contractions. The MMG, EMG and rate of perceived exertion were recorded from 11 subjects in five arm positions (0 degrees abduction and 0 degrees flexion, 45 degrees and 90 degrees flexion, 45 degrees and 90 degrees abduction) with different bilateral arm loads during 3 s for non-fatiguing (0-0.5-1 kg hand-load) and 3 min for fatiguing contractions (1 kg hand-load). The root mean square (RMS), average rectified value (ARV), mean power frequency (MNF), and median power frequency (MDF) of the MMG and EMG signals were computed and normalised with respect to the initial values obtained in the current arm position or in the reference position (0 degrees abduction and 0 degrees flexion) corresponding to the normal postural activity of the trapezius muscle. For fatiguing contractions, differences in magnitude of the increase in the RMS or ARV and decrease in the MNF or MDF were observed for EMG and MMG. The MMG amplitude and spectral changes followed the subjective sensation of fatigue and were not correlated to their EMG counterparts, suggesting that they may reflect different phenomena. For non-fatiguing contractions, normalisation to the current arm position entailed the loss of dynamic amplitude changes suggesting that a single reference contraction in the middle part of the range of movement is enough for proper normalisation of EMG and MMG signals. For fatiguing contractions, normalisation of the EMG and MMG to some extent can lead to a misleading interpretation. Assessment of the upper trapezius muscle by means of MMG may be valuable in ergonomics.

Inhibition of cyclooxygenase but not nitric oxide synthase influences effects on the human omental artery of the thromboxane A2 mimetic U46619 and 17β-estradiol

Objective: These experiments were performed to study the influence of endothelial factors on the contractile effect of the thromboxane A2 analog U46619 and on the relaxant action of 17β-estradiol on isolated human omental arteries from nonpregnant women, women with normal pregnancies, and women with preeclampsia. Study Design: Arterial rings (3 mm) with or without endothelium were suspended in organ chambers filled with Krebs buffer, 37°C, aerated with 5% carbon dioxide in air, pH approximately 7.4, for isometric tension recording. Rings were incubated with indomethacin, Nω-nitro-L -arginine, or 17β-estradiol, alone or in combination. The concentration that produced 50% of maximal effect, the area under the curve, and the maximal effect of U46619, normalized with respect to a reference contraction in response to potassium chloride, were compared. Results: Neither indomethacin nor Nω-nitro-L -arginine changed the basal tone of omental artery rings. Neither Nω-nitro-L -arginine nor removal of the endothelium affected either the contractile action of U46619 or the relaxant action of 17β-estradiol. In contrast, indomethacin potentiated the contractile effect of U46619 and abolished the inhibitory effect of 17β-estradiol in rings from all three groups. The effects of U46619 and 17β-estradiol were significantly less in rings from women with normal pregnancy than in those from women with preeclampsia. Tissues from women with preeclampsia demonstrated the highest contractile response to U46619. Conclusion: The inhibitory effect of 17β-estradiol is not due to increased production of endothelial nitric oxide but rather involves inhibitory products of the cyclooxygenase pathway. The effect of indomethacin may result from inhibited production or release of eicosanoids or from sensitization of thromboxane A2 receptors. (Am J Obstet Gynecol 2001;185:182-9.)

Sudden movements of the spinal column during health-care work

Sudden loading of the spine is believed to contribute to the development of low back disorders for people performing patient-handling tasks. A method was developed to detect sudden movements of the spine during work. Seven women working as nursing aides at a hospital served as subjects. Anterior/posterior acceleration of the spine was measured during work on the back at the level of the first thoracolumbar segment and recorded on a data logger as were electromyographic signals from the erector spinae muscle. Static reference contractions were performed 5 times during the workday. An alarm sounded each time the acceleration exceeded 0.7 g and the subjects were instructed to describe the situation that led to the acceleration. During one workday, the acceleration level exceeded 0.7 g on average 5.3 times (1–12). The subjects registered 4.2 (0–11) of the alarms and 2.5 (0–8) of these occurred during patient-handling tasks. When the acceleration was in the anterior direction (forward) the maximal EMG was 30.7% (8.7–88.1) of the maximal static EMG before the situation and 87.2% (33.0–202.2) afterwards. No evidence of muscle fatigue was found based on the reference contractions. The method developed during this study is suitable to detect sudden movements during work. Relevance to industry Sudden loading or sudden movements have not been directly measured during work. Hence, it is important to develop a method to detect sudden movements during work to be able to describe the frequency of such movements.

Assessment of Muscular Activity at Low Level - Experience from Whole-Day Emg Field Recordings

Musculoskeletal disorders of the neck and shoulders is a major problem for both the individual and the society. The preventive actions have, so fare, seldom been successful, and further research on the relation between muscular activity and disorders are needed. It has been hypothesised that, even for the lowest activity of a muscle, the same fibres may always be activated (the Cinderella hypothesis). Thus, the relative duration of muscular rest is of special interest to study. Moreover, during prolonged activity at low levels, there might be a rotation of the activation between motor units, which coincides with the occurrence of short periods of EMG silence (gaps). Hence, whole-day electromyographic recordings (EMG), especially from the trapezius muscle, and characterisation of the low-level activity during real work, is most relevant in studies of neck and shoulder disorders. However, since the signal is in the μV range and with a wide frequency content (≈10 to 1,000 Hz), it is hard to acquire and certify high quality data. The quality may be improved by use of preamplifiers and ambulatory data loggers. Moreover, by calculating, and screening, the power spectra of the EMG, the mean power frequency and an artefact index, remaining possible artefacts may be detected. By inspecting the digitised (raw) EMG, these possible artefacts are then considered, and if appropriate, rejected, thus assuring a high quality of the data. In a study of cleaners and office workers - where we considered the statistical, rather than the physiological, properties of muscular rest and gap frequency - the optimal criteria for gap duration and threshold level were practically the same as the ones earlier used. As a general measure of task load, muscular rest is more suitable than gap frequency, and normalisation to a submaximal, rather than a maximal, reference contraction may be preferable.

Sensitivity of trapezius electromyography to differences between work tasks — influence of gap definition and normalisation methods

Surface electromyography (EMG) has been used extensively to estimate muscular load in studies of work related musculoskeletal disorders, especially for the trapezius muscle. The occurrences of periods of EMG silence (gaps), the time below a predetermined threshold level (muscular rest) and various percentiles of the amplitude distribution (APDF) are commonly used summary measures. However, the effects of the criteria used to calculate these measures (e.g., gap duration, threshold level, normalisation method) on the sensitivity of these measures to accurately differentiate work loads is not well known. Bilateral trapezius EMG was recorded, for a full workday, for 58 subjects following both maximal (MVE) and submaximal (RVE) reference contractions. Gap frequency, muscular rest, and percentiles were derived for eight fundamental work tasks. The calculations were performed using different gap duration criteria, threshold levels and normalisation methods. A gap duration of less than 1/2 s, and threshold level ≈0.3% MVE for gap frequency, and ≈0.5% MVE for muscular rest, were the criteria that optimised sensitivity to task differences. Minimal sensitivity to tasks and a high sensitivity to individuals was obtained using gap frequency with a threshold level of ≈1% MVE. Normalisation to RVE, rather than MVE, improved sensitivity to differences between tasks, and reduced undesirable variability. Muscular rest was more sensitive to task differences than APDF percentiles.

Assessment of workload and arm position during different work sequences: a study with portable devices on construction workers

It is recognised that work related shoulder pain is overrepresented among construction workers compared to other occupations. Studies have shown that working with hands above shoulder level increases the shoulder load. Most studies have been confined to the laboratory. The present project was carried out to map the muscular engagement and postures of construction workers undertaking ceiling fitting, and to compare the results to those of the laboratory studies. Two ambulatory devices were used, one allowing recording of electromyographic (EMG) signals bilaterally from the trapezius muscle, and the other to record the position of both arms and back by means of measuring the angles between the vertical line and the back and both upper arms. These recordings were performed during 1.5–2 h work sequences. The results show that the work was mostly performed in an upright position, that both arms were used to a similar amount and that the workers for a large proportion of their working time had their upper arms at levels that are considered harmful in view of shoulder load. The EMG data showed that nearly 50% of the work was spent with trapezius activity that exceeded that of the reference contraction used (about 15% of maximal voluntary contraction) and that the time spent in muscular relaxation was 10%. It was concluded that the exposure of construction workers undertaking ceiling fitting meets the criteria formulated on the basis of laboratory experiments with respect to a high risk of acquiring chronic shoulder pain, due to rotator cuff tendinitis.

Mechanical output and electromyographic parameters in males and females during fatiguing knee-extensions.

The purpose of this study was to elucidate if the m. quadriceps femoris was fully activated during the first contractions of a series of repetitive maximal contractions and if there was any difference in the development of fatigue between sexes. To do this sixteen untrained subjects performed two series of contractions in an isokinetic dynamometer: one series of single maximum contractions and one series of repetitive maximum contractions. The EMG activity of m. vastus lateralis, m. vastus medialis and m. rectus femoris was recorded. The subjects were unable to perform maximum effort during the first repetitions of each trial, which might influence the results of fatigue studies, if these contractions are chosen as reference. We also found in contrast to other studies a decrease in RMS between the reference contraction and the fatigue level. We have not been able to display any difference between males and females during fatigue either in relative mechanical output nor in electromyographic parameters or experience in fatigue during isokinetic knee-extensions.

Prostanoid-Induced Contraction of the Rabbit Isolated Uterus Is Mediated by FP Receptors

Natural and synthetic prostanoid agonists were used to study the prostanoid receptors involved in contraction of the mature, isolated uterus of virgin rabbits. The prostanoids elicited contractile responses with a rank order of potency of PGF 2α, fluprostenol > PGD 2 > U-46619 > PGE 2 > carbaprostacyclin with mean EC 50 (nM) values of 4, 6, 34, 550, 1318 and >10,000, respectively. Carbachol, a muscarinic agonist given after the prostanoids to elicit a reference contraction, had a mean EC 50 value of 1.1 μM. The results show that the mature rabbit uterus is most sensitive to prostaglandin FP agonists and, thus, can be defined pharmacologically as an FP receptor preparation. These findings may facilitative investigations into the possibility of different prostanoid receptor populations. In the absence of useful competitive FP receptor antagonists, agonist potency data is particularly useful in systems where cross-species comparisons and tissue-related factors are not involved. The potent activities of the FP agonists, PGF 2α and fluprostenol, in the isolated jugular vein and uterus of the rabbit suggest that these tissues may be useful for intra-species comparisons.

Quantifying work load in neck, shoulders and wrists in female dentists.

To assess the work load in neck and upper limbs of dentists. Twelve right-handed female dentists (six with and six without a history of definite neck/shoulder disorders, pair-wise matched for age) were studied when performing authentic dental work. Electromyography (EMG) was used to quantify the muscular load of the shoulders bilaterally and of the right forearm. Positions and movements of the head and wrists were measured, using inclinometers and electrogoniometers. During work, the median load for the right upper trapezium muscle was 8.4% of the maximal voluntary EMG activity (MVE); during 90% of the time the load was > or = 3.3% MVE ("static" load). The figures were somewhat lower on the left side (7.0% and 2.5% MVE, respectively). Subjects with disorders had over all lower load levels for the trapezius muscles, although not statistically significant at < 0.05, than those without disorders. During a standardized reference contraction for the trapezius, the load was 17% MVE, and the quotient between MVE and torque [normalized to maximal voluntary torque (MVC)] was 0.5. These figures may be used for transformations. The muscular load on the right forearm was similar to the loads on the trapezius. The head was, on average, forward tilted > or = to 39 degrees, and during 10% of the time > or = 49 degrees. The left hand was held in more static positions, with palmar flexion and ulnar deviation, also reflected by lower angular velocities and repetitiveness, as compared with the right one, which was dorsiflexed. Dentists are exposed to high load on the trapezius muscles bilaterally, and steep, prolonged forward bending of the head. Further, for the wrists the postures were constrained, but the dynamic demands were low.

Characterization of NK3 receptors in rabbit isolated iris sphincter muscle.

1. Tachykinin NK3 receptors were characterized in the rabbit isolated iris sphincter muscle by use of autoradiography and in vitro functional studies. 2. [125I]-[MePhe7]-neurokinin B (NKB) (1nM), a selective NK3 receptor agonist, specifically labelled a population of NK3 receptors that were uniformly distributed throughout the rabbit iris sphincter muscle. This labelling was inhibited by unlabelled [MePhe7]-NKB (1 microM) but not by the NK1 receptor antagonist CP 99994 (1 microM). 3. In the presence of CP 99994 (1 microM), the selective NK3 receptor agonists senktide (n = 14) and [Pro7]-NKB (n = 4), and the natural preferred ligand for the NK3 receptor, NKB (n = 8), were potent contractile agents in the rabbit iris sphincter muscle. They all produced monophasic concentration-effect curves with pD2 values of 9.53 +/- 0.08, 8.56 +/- 0.09 and 9.75 +/- 0.09, and nH values of 0.93 +/- 0.03, 1.53 +/- 0.17 and 0.76 +/- 0.06, respectively. [MePhe7]-NKB (n = 12) was also a potent agonist, but produced shallow concentration-effect curves which appeared biphasic (nH = 0.45 +/- 0.04). 4. Contractile responses to senktide were surmountably antagonized in a concentration-dependent manner by the selective non-peptide NK3 receptor antagonist, SR 142801 (3-30 nM; pA2 = 8.9; slope = 0.99) and the non-peptide NK2/NK3 receptor antagonist, SR 48968 (3-30 microM; pA2 = 6.1; slope = 1.5). These pA2 values were consistent with functional rabbit NK3 receptors more closely resembling guinea-pig and human NK3 receptors, than rat NK3 receptors. SR 142801 (10-100 nM) and SR 48968 (3 and 30 microM) inhibited responses to low (< or = 1 nM) but not higher (> 1 nM) concentrations of [MePhe7]-NKB, and concentration-effect curves to [MePhe7]-NKb became steeper and monophasic in the presence of either antagonist. 5. SR 142801 (3-30 nM) and SR 48968 (3-30 microM) also surmountably antagonized concentration-effect curves to [Pro7]-NKB and NKB, although results were more difficult to interpret, since the relationship between log concentration-ratios and the concentration of antagonist used did not adhere to the Schild equation. However, analysis of data with the lowest concentration of SR 142801 (3 nM) tested against NKB, and SR 48968 (3 microM) tested against [Pro7]-NKB and NKB, yielded apparent pA2 estimates of 9.3, 6.8 and 6.4, respectively, consistent with blockade of NK3 receptors. 6. SR 142801 (100 nM) had no effect on contractions induced by transmural nerve stimulation (2 Hz, 0.3 ms, 20 V for 30 s), whereas CP 99994 (1 microM) abolished these responses. 7. Phenoxybenzamine pretreatment (20 microM, 10 min) markedly reduced maximum responses to [MePhe7]-NKB (from 101 +/- 6.2% to 38 +/- 9.5% reference contraction, n = 4) and induced a marked (10 fold) rightward shift in the concentration-effect curve. The residual responses to [MePhe7]-NKB after phenoxybenzamine pretreatment were unaffected by 1 microM CP 99994 (maximum response = 41 +/- 9.4%, n = 4). 8. These results demonstrate autoradiographically and functionally, the presence of NK3 receptors in rabbit iris sphincter muscle that mediate contractile responses to NK3 receptor agonists, but not to sensory trigeminal nerve simulation. The present data with senktide and selective NK3 receptor antagonists suggest that functional rabbit NK3 receptors more closely resemble human and guinea-pig NK3 receptors than rat NK3 receptors. However, the pharmacological profiles of [MePhe7]-NKB, SR 142801 and SR 48968 suggest the presence of an 'atypical' NK3 receptor or a heterogeneous population of NK3 receptors in this tissue.

Effects of selected vasoconstrictor agonists on isolated omental artery from premenopausal nonpregnant women and from normal and preeclamptic pregnant women

OBJECTIVE: Our purpose was to compare the responsiveness of omental resistance arteries from nonpregnant women and from normotensive and preeclamptic pregnant women to selected contractile agonists. STUDY DESIGN: Omental artery rings with intact endothelium from normotensive premenopausal nonpregnant women and from normal and preeclamptic pregnant women were mounted in Krebs-bicarbonate solution in organ baths for isometric tension recording. After the presence of endothelium was confirmed, cumulative concentrations of norepinephrine, serotonin, U46619, and endothelin-1 were added. Concentration-response curves were constructed and expressed as percentage of a reference 60 mmol/L potassium chloride contraction. Data analysis was by repeated-measures analysis of variance, Newman-Keuls test, and paired or unpaired Student t test, as appropriate. Statistical significance was by two-tailed p < 0.05. RESULTS: Endothelin-1 and U46619 increased tension similarly in all three groups. Norepinephrine increased tension in nonpregnant vessels to a greater extent than in either preeclamptic or pregnant vessels (nonpregnant 114.3 ± 5.42% vs pregnant 65.2% ± 10.5%, p <0.05). Nonpregnant omental artery developed significantly greater tension than did pregnant tissue at three concentrations of norepinephrine (10 -5 mol/L, 3 × 10 -5 mol/L, 10 -4 mol/L), and preeclamptic vessels developed more tension than that from normal pregnant vessels at 3 × 10 -6 mol/L ( p = 006) and 10 -5 mol/L ( p <0.05). There was a negligible change in tension with increasing concentrations of serotonin in the vessels from nonpregnant women; serotonin-induced contraction in the omental arteries from normotensive pregnant women and preeclamptic patients was <6% of the potassium chloride reference contraction, but this was significantly ( p <0.05) different from that of the nonpregnant women. CONCLUSIONS: Omental artery segments from nonpregnant, normotensive pregnant and preeclamptic women contract similarly to endothelin-1 and U46619 but exhibit variable responses to norepinephrine and serotonin. (AM J OBSTET GYNECOL 1996;174:687-93.)

Normalizing upper trapezius EMG amplitude: Comparison of ramp and constant force procedures

The present study compared three procedures for normalization of upper trapezius surface electromyographic (EMG) amplitudes: (a) a ramp procedure (providing data in per cent of maximal voluntary contraction, MVC); (b) a constant force procedure based on two reference contractions (two-force procedure) (%MVC) and (c) a procedure expressing muscle activation in per cent of a reference voluntary electrical activity (%RVE). The study also evaluated the repeatability of the ramp and the RVE procedures and estimated the force exertion (%MVC) corresponding to the RVE. To illustrate the ergonomic effect of different normalization procedures, trapezius EMG during two work tasks was compared after normalization by the two-force and the RVE procedures. Fifteen subjects participated in the whole study. We found that force estimates obtained by the ramp procedure equation could be translated to force estimates obtained by the two-force procedure by the equation: %MVC 2force = − 0.6 + 0.9∗%MVC ramp, although with a considerable imprecision due to large inter-individual differences. In the ramp procedure, the intra-individual test-retest coefficient of variation (CV) depended on the force level; it was 45% at 5% MVC and 10% at 30% MVC. The CV of the RVE was 15%. The reference contraction used in the RVE procedure corresponded from 13–79% MVC (median 33%MVC). The load reducing effect of an ergonomic intervention was less obvious with the RVE procedure than with the two-force procedure due to a larger inter-individual variation. The advantages and disadvantages of the different procedures are discussed.