Electro and acoustic myography for noninvasive assessment of lumbar paraspinal muscle function

In 31 normal subjects (17 male), aged 19-48 years, and 8 patients with chronic low back pain (4 male), aged 37-55 years, the repeatability of surface recordings of acoustic myography (AMG) and electromyography (EMG) were examined in the lumbar paraspinal muscles. Five isometric test positions were examined. In 21 of the normal subjects, four positions tested were: quiet standing, half extension from prone lying, full extension from prone with and without resistance. In 10 of the normal subjects and the 8 back pain patients, a standardised, unsupported horizontal position with the upper body over the end of a couch was tested. The AMG and EMG signals were full-wave rectified and integrated (iAMG and iEMG). The variability of recordings during repeated 5-s isometric contractions was assessed by analysis of variance (ANOVA) and the coefficient of variation (CV) was calculated from the ANOVA. Both recording techniques produced the most repeatable results during the unsupported, horizontal hold position. In the normal subjects, CV were, iAMG 5.6%, iEMG 4.9%; and in the patients, iAMG 4.4%, iEMG 2.6%. The CV for the other four isometric test positions ranged from 15.3% to 29.4% for iAMG, and 8% to 15.7% for iEMG. These results demonstrated that a controlled test manoeuvre for examining AMG and EMG of the paraspinal muscles was vital for repeatable recordings. The CV for the standardised, horizontal position were lower than for previously published results.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of test position on neck muscle fatigue in healthy controls

BackgroundIt has been suggested that increased fatigue of neck muscles could be related to neck pain. However, studies on the matter present contradicting results which could be explained by the different test positions used.PurposeThe purpose of this study was to investigate the influence of test position on muscle fatigue of neck flexor and extensor muscles in healthy controls.MethodsTwenty-five women without neck pain sustained neck flexion and neck extension isometric contractions at 25% and 75% of their maximal voluntary contraction (MVC) in two test positions: sitting and supine lying. Using surface electromyography, the change over time of the median frequency of the power spectrum (MDF slope) of the myoelectric signal of the sternocleidomastoid and splenius capitis muscles was measured and compared between both positions.ResultsAt 75% MVC, splenius capitis muscles presented higher fatigue in lying compared to sitting, while sternocleidomastoid demonstrated no difference between positions. No statistically significant effect of test position was found at 25% MVC for both sternocleidomastoid and splenius capitis muscles as they generally did not present myoelectric manifestations of fatigue.ConclusionThese results underline the need to standardise the test position when investigating neck muscle fatigue, especially for neck extensors at high loads.     

Intracompartmental pressure of the anterior tibial compartment as a function of body and joint position

We measured the intracompartmental pressure in the anterior tibial compartment of 27 volunteers under different experimental conditions. First we recorded the pressure in the proximal, middle, and distal third of the compartment as well as at different depths of the muscle. Thereafter the pressure was measured in the lying, sitting and standing positions, and at different positions of the knee and ankle joint. There was no difference in pressure in the various parts of the muscle. However, there was a significant difference between the lying, sitting and standing positions. Dorsal flexion of the ankle resulted in an increase in the intracompartmental pressure in dorsiflexion and plantarflexion of the ankle.     

Changes in the H Reflex Preceding Voluntary Movements of the Contralateral Lower Limb in Humans

In electromyographic studies on healthy subjects, we recorded the H reflex from the right m. soleus and measured changes in the magnitude of this reflex response related to voluntary movements of the contralateral lower limb performed according to a visual signal. The effects of back and plantar flexions of the contralateral foot of the tested subject in the lying and standing positions were examined. Changes in the H reflex magnitude began to be recorded 60 to 90 msec prior to voluntary movements of the contralateral limb. When the subject was in the lying position, these changes looked like facilitation of the H reflex at both types of movement of the contralateral foot. When the subject stood, facilitation preceded back flexion of the foot of this extremity, while plantar flexion was preceded by inhibition of the tested H reflex. Our results show that the pattern of preliminary changes in the muscle tone of one of the lower limbs is determined by the type of future movement of another limb and peculiarities of the support function realized by this limb.     

Symmetry-based resistance as a novel means of lower limb rehabilitation

Robotic devices hold much promise for use as rehabilitation aids but their success depends on identifying effective strategies for controlling human-robot interaction forces. We developed a robotic device to test a novel method of controlling interaction forces with the intent of improving force symmetry in the limbs. Users perform lower limb extensions against a computer-controlled resistive load. The control software increases resistance above baseline in proportion to lower limb force asymmetry (balance between left and right limb forces). As a preliminary trial to test the device and controller, we conducted two experiments on neurologically intact subjects. In experiment 1, one group of subjects received symmetry-based resistance while performing lower limb extensions (n=10). A control group performed the same movements with constant resistance (n=10). The symmetry-based resistance group improved lower limb symmetry during training (ANOVA, p<0.05), whereas the control subjects did not. In experiment 2, subjects (n=10) successfully used symmetry-based resistance to alter their lower limb force production towards a target asymmetry (ANOVA, p<0.05). These studies suggest that symmetry-based resistance may hold rehabilitation benefits after orthopedic or neurological injury. Specifically, performing strength training therapy with this controller may allow hemiparetic individuals to focus better on increasing strength and neuromuscular recruitment in their paretic limb while experiencing symmetric limb forces.     

Do introns favor or avoid regions of amino acid conservation?

Are intron positions correlated with regions of high amino acid conservation? For a set of ancient conserved proteins, with intronless prokaryotic but intron-containing eukaryotic homologs, multiple sequence alignments identified residues invariant throughout evolution. Intron positions between codons show no preferences. However, introns lying after the first base of a codon prefer conserved regions, markedly in glycines. Because glycines are in excess in conserved regions, this behavior could reflect phase-one introns entering glycine residues randomly in the ancestral sequences. Examination of intron positions within codons of evolutionarily invariable amino acids showed that roughly 50% of these introns are bordered by guanines at both 5'- and 3'-ends, 25% have a G only before the intron, and 5% have a G only after the intron, whereas about 20% are bordered by nonguanine bases.     

The effect of prone posture on nasal temperature in children in relation to induction of staphylococcal toxins implicated in sudden infant death syndrome

The incidence of sudden infant death syndrome (SIDS) has declined in response to campaigns discouraging the prone sleeping position. Recent work suggests some SIDS death may be in response to bacterial toxins produced in the upper airway. A minimal temperature of 37 degrees C is required for induction of the pyrogenic toxins of Staphylococcus aureus identified in many SIDS infants. This aim of this study was to test the hypothesis that the prone position raises the temperature of the upper airways in children. A pilot study of 10 children (aged 3-8) and a main study of 30 children were carried out. Nasal septal temperatures were measured with an infra-red thermometer with the subjects in upright and prone positions under controlled conditions of ambient temperature and humidity. In both the pilot study and main study, nasal temperatures in the prone position were significantly higher (P < 0.01) Five subjects' prone readings were 37 degrees C or higher. These findings suggest that lying prone raises the upper airway surface temperature towards that required for toxin production. This could be one means by which the prone sleeping position contributes to the risk of SIDS.     

Evolution Rates of Genes on Leading and Lagging DNA Strands

One of the main causes of bacterial chromosome asymmetry is replication-associated mutational pressure. Different rates of nucleotide substitution accumulation on leading and lagging strands implicate qualitative and quantitative differences in the accumulation of mutations in protein coding sequences lying on different DNA strands. We show that the divergence rate of orthologs situated on leading strands is lower than the divergence rate of those situated on lagging strands. The ratio of the mutation accumulation rate for sequences lying on lagging strands to that of sequences lying on leading strands is rather stable and time-independent. The divergence rate of sequences which changed their positions, with respect to the direction of replication fork movement, is not stable—sequences which have recently changed their positions are the most prone to mutation accumulation. This effect may influence estimations of evolutionary distances between species and the topology of phylogenetic trees. Received: 24 July 2000 / Accepted: 16 January 2001     

Mandibular border positions in eugnathic subjects during the second bite lifting

This research was aimed at performing a clinical functional analysis during the second bite lifting, in order to define mandibular border positions and possible differences by sex and/or age. Out of a total of 9680 examined children from the region of Medimurje, Croatia, 103 were found to be eugnathic, with dentition in occlusion during the phase of the second bite lifting. All the eugnathic patients belonged to the class I by Angle, without any caries, fillings or extracted teeth. They were divided into three predefined groups for the sake of comparison. The obtained values of mandibular border positions in eugnathic subjects during the second bite-lifting phase vary with age and with the number of present permanent teeth in occlusion. Generally, all the values are higher in girls than in boys, which speaks in favour of the assumption that mandibular border positions are determined by sex, hormonal activity, growth and intercuspidation. Also, girls show a higher TMJ flexibility as well as a higher mandibular mobility. The knowledge of these facts will contribute to a more precise treatment in child prosthetics and pedodontics.     

Comparison of contact pressures measured at the sacrum of young and elderly subjects

Contact (interface) pressure measurements were made between the sacrum of groups of young and elderly subjects lying upon two special mattresses used to prevent pressure sores. One mattress was an alternating air pressure mattress, the other a foam mattress. Contact pressures were measured using a hydraulic sensor taped directly to the skin over the sacrum. All mean pressures and ‘pressure impulses’ (total applied pressure per standard time period) appeared higher when measured among the elderly subjects. Compared with the pressures measured from young subjects, the maximum contact pressures were significantly higher (p < 0.05) on both mattresses, with the pressure impulse higher while lying upon the foam mattress (p < 0.05).     

Minimizing animal numbers: the variable-criteria sequential stopping rule

The variable-criteria sequential stopping rule (SSR) allows an investigator to use a few subjects at a time to determine whether a planned experiment is worth pursuing without increasing the rate of false discoveries (type I errors). The SSR is appropriate whenever testing a null hypothesis if the experiment can be conducted in stages. The investigator adds a predetermined number of subjects at each stage and tests repeatedly for significance until the experiment is stopped because: (1) a significant effect is detected; (2) the effect is clearly not going to be significant; or (3) the predetermined maximal number of subjects has been reached. Two crucial features of the SSR are that it holds the probability of a type I error constant and maintains excellent power. The method is more efficient than is performing a typical significance test after a power analysis because SSR can require 30% fewer subjects to achieve the same power. The variable-criteria SSR provides a formal method for assuring the use of a minimal number of animals. This article provides practical examples of how to use the SSR in combination with a t test, one-way ANOVA, one-way ANOVA with a planned contrast as the focus of the stopping rule, or, in limited circumstances, multifactorial ANOVA.     

The effect of electromagnetic stimulation on the parameters of muscular strength

A new way to develop muscular strength using electromagnetic stimulation (ES) of muscles during their voluntary contractions has been described. The experiment involved 18 healthy men divided into the control group (CG) and the experimental group (EG) with equal parameters of muscular strength. In performing training exercises (the foot plantar flexion), the m. gastrocnemius of the subjects of the EG was exposed to ES (1.8 T, 5 Hz). The subjects of the CG performing the same exercises did not receive ES. The power torque of the foot plantar flexion in the EG significantly increased (24%) after 10 days of training. The power torque of the foot plantar flexion in the control subjects did not significantly change. We suppose that the increase in the muscular strength in the subjects of the EG was due to the activation of high-threshold motor units effected by ES.     

NMR solution structure of the angiostatic peptide anginex

Anginex, a designed peptide 33mer, is known to function both as an antiangiogenic and bactericidal agent. Solving the NMR solution structure of the peptide is key to understand better its structure-activity relationships and to design more bioactive peptides and peptide mimetics. However, structure elucidation of anginex has been elusive due to subunit exchange-induced resonance broadening. Here, we found that performing NMR structural studies in a micellar environment abolishes exchange broadening and allows the structure of anginex to be determined. Anginex folds in an amphipathic, three-stranded antiparallel beta-sheet conformation with functionally key hydrophobic residues lying on one face of the beta-sheet and positively charged, mostly lysine residues, lying on the opposite face. Structural comparison is made with a homologous, yet relatively inactive peptide, betapep-28. These results contribute to the design of peptidomimetics of anginex for therapeutic use against angiogenically-related diseases like cancer, as well as infectious diseases.     

Estimation of 50-Hz Electrically Vs. Magnetically Generated Body Currents in Sleeping Subjects

The exposure from low-frequency electric and magnetic fields to sleeping subjects was analyzed at 343 sites. To establish the exposure due to electric fields, a new method was used to measure the current density on the body surface of the test subjects lying in their beds. The exposure due to magnetic fields was determined by short-term measurements of the magnetic flux density using induction coils. The exposures from the electric and magnetic fields were compared. The result was that, in general, the electric fields contribute much more to the total exposure than the magnetic fields.     

Significance of exercise and bed rest in pregnancy--study on the lying postures of gravidas during sleep (2)

For the purpose of determining the most reasonable lying posture for pregnant women, we investigated the lying positions of both 247 non-pregnant women and 302 pregnant women during sleep. As for the rate of each position during the entire period of observation, 33.2% of the non-pregnant women were in the supine position, 41.2% in the lateral position, 18.4% in Sims' position and 7.1% in the prone position. In the pregnant group, the rate of supine position, simple lateral position and Sims' position was 34.2%, 52.2% and 12.7%, respectively, but the rate of the prone position was limited to 0.8%. All of the gravidas assuming the prone position were at less than 16 weeks of gestation. Non-pregnant women could sleep in a variety of positions, but pregnant women could assume the prone position during sleep only in the stage when the abdomen is not yet prominent or distended. Pregnant women were restricted significantly, either consciously or unconsciously, with progress in gestation.     

Validation and Reliability of a Classification Method to Measure the Time Spent Performing Different Activities

The aim of this study was to validate the performance and reliability of results obtained from a classification model that measures time spent performing activities in confined (CE) and unrestricted (UE) environments. In CE, participants wore a pair of biaxial and/or triaxial accelerometers while performing pre-determined training activities classified as variants of lying down, dynamic standing, sitting, walking and running on two separate days. A classification model trained with activities performed in a specific order during the first day was developed to validate the activities performed in a random order on the second day (CE) and over 24 hours on a separate day (UE). The performance of the classification model was validated against triaxial accelerometers using six (x, y and step counts for arm and thigh) or eight (same as six features plus z axis) features. The reliability of the classification model was tested in both environments using six features. Results revealed an overall accuracy of 94% in CE and 90% in UE. The sensitivity in CE and UE was 94% and 95% for lying down, 88% and 80% for dynamic standing, 97% and 89% for sitting, 96% and 78% for walking and 90% and 64% for running, respectively. No significant differences were noted between performances obtained with six or eight features. Results were highly reproducible in both environments. The results obtained from the classification model were accurate and reproducible, and highlight the potential use of this approach in research to quantify the time spent performing different activities.     

Effect of posture on inspiratory muscle electromyogram response to hypercapnia

The aim of our study was to examine the effect of posture on inspiratory muscle activity response to hypercapnia. Recent research has revealed that in normal subjects the activation of the rib cage muscles and of the diaphragm is actually greater in the upright than in the supine position during resting tidal breathing. In this study we examined whether the upright position necessarily entails a greater activation of the inspiratory muscles also under conditions of ventilatory stress. For this purpose we compared the responses to CO2-rebreathing in the supine and sitting positions in five volunteers, by simultaneously recording the electromyogram of the diaphragm (EMGdi) and the intercostal muscles (EMGint). The electromyogram was recorded by means of surface electrodes to measure the EMG amplitude. While the slopes of ventilatory (VE) response to increasing arterial CO2 tension (PaCO2) were similar in the two positions, both the EMGdi-VE and EMGint-VE relationship showed steeper slopes in the supine than in the sitting position. In each CO2 run the increases in EMGdi were linearly related to those in EMGint. This relationship was not affected by the body position. These results suggested that, in spite of similar ventilatory responses to CO2-rebreathing in the lying and sitting positions, the supine position, in humans, required a higher activation of the inspiratory muscles.     

Characteristics of the human EEG during cognitive-mnemenic activity under hypoxic conditions

The amplitude-frequency and spatiotemporal characteristics of the EEGs of subjects performing various cognitive-mnemenic activities under the conditions of graduated hypoxia were studied. The quickness and correctness of test performance were significantly decreased beginning from the sixth minute of hypoxia as compared to normoxic conditions. The amplitude and mean period of the dominant EEG activity in this functional state were higher than in the same tests performed under normoxic conditions and lower than in the case of hypoxia not accompanied by the performance of tests. The spatiotemporal characteristics of the EEG under hypoxic conditions displayed both the characteristics typical of hypoxia (a decrease in EEG cross-correlation within anterior cortical regions) and those typical of cognitive-mnemenic activity (an increase in the correlation between the EEGs of distant zones of anterior and posterior cortical regions). It is assumed that the “intermediate” EEG pattern observed in subjects performing cognitive-mnemenic tests under hypoxic conditions reflects opposite effects of hypoxia and intellectual effort on the functional activity of brain neurons.     

An Evaluation of Exercise Pen Use by Circus Tigers (Pathera tigris tigris)

This study quantified the behavior of 11 tigers during periodic access to an exercise pen throughout the day and night. The study determined the amount of time spent in the pen and the percentage of time spent performing stereotypic pacing, normal locomotor behavior, and lying down while in the pen. Average access to the exercise pen was 10 hr 49 min overnight and 5 hr 30 min during the day. At night, the tigers spent 29.1% of their time in the exercise pen, during which they paced 19.6% and performed normal locomotor behavior for 23.1% of that time. By day, they spent 40.4% of their time in the exercise pen, during which they paced 10.0% and performed normal locomotor behavior 35.7% of that time. The tigers spent the rest of the time in the pen lying down. Overall, tigers will utilize an exercise pen, spending a greater percentage of time in the pen during the day than at night and also performing less stereotyped pacing than at night.