Ground reaction forces during locomotion in simulated microgravity

The role of ET and KATP channel in hypoxia-induced negative chronotropic effect of pacemaker cells in rabbit sinoatrial node was studied with intracellular microelectrode technique. The results obtained were as follows: (1) Hypoxia produced a progressive decrease in the velocity of diastolic depolarization (VDD) of pacemaker cells resulting in a reduced rate of pacemaker firing (RPF), and induced a decrease in APD, especially APD50. (2) KATP channel opener cromakalim markedly induced a negative chronotropic effect in a concentration-dependent manner and significantly shortened APD50. KATP channel blocker glibenclamide alleviated the effects of hypoxia on pacemaker cells, thereby suggesting the involvement of KATP channel in the hypoxia-induced effects. (3) By superfusion of ET-1, the hypoxia-induced decrease in RPF was remarkably potentiated and the occurrence of pacemaker arrest was shifted to an earlier time. The hypoxia-induced effects could be effectively attenuated after pretreatment with BQ-123, implying the role of endogenous ET-1 release in hypoxia-induced effects. It is concluded that the negative chronotropic effect and the decrease in APD induced by hypoxia may be attributed to the activation of KATP channel and the release of endogenous ET.     

EMG of slow and fast ankle extensors of cat during posture, locomotion, and jumping

Methods are described for the preparation in vivo of 35S-methionine-labelled influenza viruses, the purifiction of the nucleoprotein (NP) and matrix (M) proteins and the separation of peptides obtained by protease digestion by two-dimensional thin-layer chromatography. The maps of the M proteins of A/Okuda/57(H2N2) and A/Finland/4/74(H3N2) were very similar overall but differed in three peptides. Hence they could be clearly distinguished. Maps of the NP proteins of the same strains showed a greater number of differences. A recombinant strain having the haemagglutinin and neuraminidase of the A/Finland/4/74 parent and the virulence of the A/Okuda/57 parent was shown to have the M and P proteins of A/okuda/57.     

Amplitude and bilateral coherency of facial and jaw-elevator EMG activity as an index of effort during a two-choice serial reaction task

In earlier studies, positive but inconsistent relationships have been reported between mental effort and electromyogram (EMG) amplitude in task-irrelevant limb muscles. In this study, we explored whether facial EMG activity would provide more consistent results. Tonic EMG activity of six different facial and jaw-elevator muscles was bilaterally recorded during a two-choice serial reaction task with paced presentation of auditory or visual signals. In Experiment 1, task load (signal presentation rate) was kept constant for 20 min at the level of the subject's maximal capacity. In Experiment 2, task load was increased in a stepwise fashion over six successive 2-min periods from sub- to supramaximal capacity levels. EMG amplitude and coherency between momentary bilateral amplitude fluctuations were measured. In Experiment 1, EMG amplitude of frontalis, corrugator supercilii, and orbicularis oris inferior showed a strong gradual increase throughout the task period, whereas taks performance remained fairly stable. Orbicularis oculi, zygomaticus major, and temporalis EMG showed a much smaller increase or no increase. In Experiment 2, the first three muscles showed a fairly consistent increase in EMG amplitude with increasing task load. Orbicularis oculi and zygomaticus major were not active until task load became supramaximal. Effects of stimulus modality or laterality were not found in any experiment. These results are consistent with the notion that EMG amplitude of frontalis, corrugator, and orbicularis oris provides a sensitive index of the degree of exerted mental effort.     

Ground reaction forces in horses, assessed from hoof wall deformation using artificial neural networks

An artificial neural network (ANN) was developed to investigate whether hoof wall deformation could be used to determine ground reaction forces (GRF) in horses. The ANN was taught this relationship under certain conditions and was able to generalise this knowledge to conditions for which it was not trained before. To acquire data to train and test the ANN, a horse was equipped with strain gauges attached to the dorsal, lateral and medial parts of the hoof to assess hoof wall deformation. A force plate was used to measure the GRFs. Both hoof wall deformation and GRF were recorded simultaneously at different speeds, gaits, surfaces and loads. An ANN was trained with some of these data, and subsequently provided with strain gauge recordings of strides, not used for training. By comparing the GRF calculated by the ANN based on the hoof wall deformation with that recorded simultaneously by the force plate, the generalisability of the ANN was determined. It was found that an ANN is capable of 'learning' the relationship between hoof wall deformation and GRF, and to generalise it to a wide range of new conditions. This technique enables assessment of GRF under difficult conditions, such as on a treadmill or on surfaces where a force plate cannot be employed.     

Peripheral neuropathy effect on ankle inversion and eversion detection thresholds

A servo-controlled foot platform was used to quantify, in upright stance, the thresholds for sensing ankle inversion and eversion movements in seven geriatric patients with peripheral neuropathy (PN) confirmed by nerve conduction studies and seven age- and gender-matched (C) controls with normal nerve conduction function. The PN group had a 4.6-fold larger (p = 0.0026) threshold (mean [SD] 1.37 [1.74]degrees) for perceiving the presence and direction of an ankle rotation at a 75% rate of success (TH75) than did the C group (0.3[0.17]degrees). Inversion acuity was approximately twice that of eversion acuity in both groups. The PN group demonstrated better proprioceptive acuity in unipedal stance than in bipedal stance, whereas no such difference was found in the C group. Semiquantitative clinical tests of PN group proprioception at the ankle performed in the seated position failed to demonstrate significant differences from controls save in one case; however, the results of such tests at the toe were abnormal in all patients. In the geriatric population, PN is associated with deficits in ankle proprioception known theoretically to hamper maintenance of unipedal balance. It is significant that these deficits are associated with a clinically demonstrable loss of position sense at the toe but not the ankle.     

Telemetry system to record force and EMG from cat ankle extensor and tibialis anterior muscles

The purpose of this technical note is to present the design of an eight-channel telemetry system of dimensions and weight small enough to record muscular forces and EMGs simultaneously from gastrocnemius, soleus, plantaris and tibialis anterior muscles of a freely moving cat. All schematics for constructing the telemetry device are shown in detail. Using this system, we were successful in measuring force and EMG data of all four instrumented muscles in freely moving animals. The telemetry system presented here has the advantage over a conventional cable system that recordings may be obtained at any time in the freely moving animal without interference by an experimenter.     

Acute inversion injury of the ankle: magnetic resonance imaging and clinical outcomes

This study was undertaken to compare the clinical and magnetic resonance imaging results of 24 patients who had sustained ligament injuries after acute inversion injury of the ankle. On magnetic resonance imaging, the following lesions were detected: anterior talofibular ligament tear in 23 patients, calcaneofibular ligament lesion in 15, posterior talofibular ligament lesion in 11, interosseous talocalcaneal ligament lesion in 13, cervical ligament lesion in 12, and deltoid ligament lesion in 8. Compared with the clinical outcome at the follow-up study, there was a statistically significant relationship between interosseous talocalcaneal ligament lesion and each of giving way, pain, and limitation of ankle motion; between cervical ligament lesion and both giving way and pain; and between deltoid ligament lesion and giving way (P < 0.05).     

Lip EMG activity during vowel production in apraxia of speech: phrase context and word length effects

This investigation examined the timing relationships of EMG activity underlying vowel production in 2 normal individuals and in 2 individuals with marked-to-severe apraxia of speech of approximately two-and-one-half years duration. The timing of lip muscle activity was investigated in monosyllabic words embedded in phrases and in syllable word stems as a function of changes in word length. Specifically, the onset and offset of EMG activity of lip muscles used for production of /u/ in the monosyllables and word stems were examined. The results revealed that the relative amounts of time devoted to onset and offset of EMG activity for lip rounding are disorganized in apraxia of speech. Word length appeared to affect the timing of the onset of muscle activity for both the normal speakers and the speakers with apraxia of speech. Word length also influenced the offset of muscle activity, but its effect was less systematic for the speakers with apraxia of speech. The findings suggest that termination of EMG activity may be at least as disturbed as the initiation of EMG activity in apraxia of speech.     

Mental stress of long duration: EMG activity, perceived tension, fatigue, and pain development in pain-free subjects

The study examined the relationship between pain development in the shoulder, neck, and facial regions and the EMG activity of underlying muscles, during prolonged exposure to a mental stressor. The subjective perception of tension and fatigue was recorded. Thirty-six subjects were exposed to a two-choice reaction-time test for 1 hour. Electromyographic (EMG) recordings were performed bilaterally over the frontalis, temporalis, splenius, and trapezius muscles. Pain and perceived tension were scored on a visual analog scale, and fatigue on a Borg scale. Pain development was most pronounced in the shoulder and neck region. There was a weak tendency of those reporting pain in the shoulder region to generate higher EMG activity in the trapezius relative to those with no shoulder pain at the end of the test. No such relationship was observed for the other muscles. Perceived tension during the test was weakly related to pain and strongly related to fatigue at the end of the test, but not to EMG level. It is concluded that the mean level of the EMG response is of little consequence for pain development during stressful conditions. It is argued that other physiological responses such as prolonged activity in low-threshold motor units, whereby the surface EMG response can serve as a marker, can be important for shoulder pain originating in the trapezius muscle.     

The relationship between EMG activity and extensor moment generation in the erector spinae muscles during bending and lifting activities

The relationship between EMG activity and extensor moment generation in the erector spinae muscles was investigated under isometric and concentric conditions. The full-wave rectified and averaged EMG signal was recorded from skin-surface electrodes located over the belly of the erector spinae at the levels of T10 and L3, and compared with measurements of extensor moment. The effects of muscle length and contraction velocity were studied by measuring the overall curvature (theta) and rate of change of curvature (d theta/dt) of the lumbar spine in the sagittal plane, using the '3-Space Isotrak' system. Isometric contractions were investigated with the subjects pulling up on a load cell attached to the floor. Hand height was varied to produce different amounts of lumbar flexion, as indicated by changes in lumbar curvature. The extensor moment was found to be linearly related to EMG activity, and the 'gradient' and 'intercept' of the relationship were themselves dependent upon the lumbar curvature at the time of testing. Concentric contractions were investigated with the subjects extending from a seated toe-touching position, at various speeds, while the torque exerted on the arm of a Cybex dynamometer was continuously measured. Under these conditions the EMG signal (E) was higher than the isometric signal (E0) associated with the same torque. E and E0 were related as follows: E0 = E/(1 + A d theta/dt), where A = 0.0014 exp (0.045P) and P = percentage lumbar flexion. This equation was used to correct the EMG data for the effect of contraction velocity. The corrected data were then used, in conjunction with the results of the isometric calibrations, to calculate the extensor moment generated by the erector spinae muscles during bending and lifting activities. The extensor moment can itself be used to calculate the compressive force acting on the lumbar spine.     

Force treadmill for measuring vertical and horizontal ground reaction forces

We constructed a force treadmill to measure the vertical, horizontal and lateral components of the ground-reaction forces (Fz, Fy, Fx, respectively) and the ground-reaction force moments (Mz, My, Mx), respectively exerted by walking and running humans. The chassis of a custom-built, lightweight (90 kg), mechanically stiff treadmill was supported along its length by a large commercial force platform. The natural frequencies of vibration were >178 Hz for Fz and >87 Hz for Fy, i.e., well above the signal content of these ground-reaction forces. Mechanical tests and comparisons with data obtained from a force platform runway indicated that the force treadmill recorded Fz, Fy, Mx and My ground-reaction forces and moments accurately. Although the lowest natural frequency of vibration was 88 Hz for Fx, the signal-to-noise ratios for Fx and Mz were unacceptable. This device greatly decreases the time and laboratory space required for locomotion experiments and clinical evaluations. The modular design allows for independent use of both treadmill and force platform.     

Strength and pain measures associated with lateral epicondylitis bracing

BACKGROUND: In the experiment described here, we investigated the effects of the immunosuppressants FK506 and leflunomide (Lef) on the survival of hamster hearts and liver xenografts in Lewis rats. METHODS: Lewis rats were used as recipients of hamster heart or liver grafts using different regimens of FK506 and Lef. Donor-matched heart grafts were transplanted into long-term surviving Lewis rat recipients of hamster xenografts to test donor-specific prolongation of xenograft survival. Hyperimmune, late xenograft rejection, and naive sera were transferred into long-term surviving Lewis rat recipients of hamster heart xenografts to determine whether these sera could inhibit the efficacy of donor-specific long-term survival. Anti-donor-specific antibodies were analyzed by flow cytometry. RESULTS: After a short induction with FK506 plus Lef, maintenance treatment with FK506 alone was sufficient to prolong survival of hamster xenografts. All hamster heart and four of six hamster liver xenografts survived for more than 3 months. Second hamster hearts were permanently accepted by Lewis rats bearing long-term surviving hamster heart xenografts when rats were treated with FK506 monotherapy (mean survival time >60 days, n=4). Long-term surviving hamster heart grafts were rejected after transfer of hyperimmune serum but not late xenograft rejection serum or naive serum. Lef and FK506 significantly reduced the production of anti-donor-specific antibodies in Lewis rats transplanted with hamster liver and heart xenografts. CONCLUSION: Long-term survival of hamster liver and heart xenografts in Lewis rats could be induced by a regimen of short-term FK506 in combination with Lef followed by FK506 monotherapy. The acquired sensitivity of late xenoreactivity to FK506 reflects primarily a modification in the host immune response to the hamster graft.     

Relationship between velopharyngeal dimensions and palatal EMG during progressive hypercapnia

To examine the contribution of specific palatal muscles to velopharyngeal dimensions, we recorded electromyographic (EMG) activity in the levator veli palatini, the tensor veli palatini, and the palatoglossus while examining the velopharynx (VP) with videoendoscopy in eight awake normal adults. Simultaneous display of VP images and airflow provided precise timing of events. Video images and EMG signals were recorded during progressive hypercapnia. Every tenth breath was analyzed. For each selected breath, VP area, anteroposterior and lateral diameters, and EMG activity were determined at five points: beginning, middle, and end of inspiration and middle and end of expiration. VP measurements changed significantly during the respiratory cycle. Although maximum area was measured at end inspiration or middle expiration and minimum area at the beginning or end of the breath, respiratory-related changes in VP measurements and EMG activity were characterized by substantial inter- and intrasubject variability. This variability is similar to velopharyngeal behavior during nonrespiratory tasks and suggests that upper airway patency is determined by multiple factors.     

Coping with stress during childhood and adolescence.

In this article, research on how children and adolescents cope with stress and coping's role in reducing the adverse psychological states associated with stress is reviewed. Child and adolescent coping is reflected in seven different lines of research—infants' responses to maternal separation, social support, interpersonal cognitive problem-solving, coping in achievement contexts, Type A behavior pattern in children, repression–sensitization, and resilience to stress. A variety of different coping resources, styles, and specific strategies are important in successfully adapting to stress, including efforts that focus directly on the problem, as well as attempts to deal with adverse emotions associated with stress. Directions for future research are identified, emphasizing the need for more systematic comparisons of coping across different types of stress and over time in response to a single stressful episode. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

High-frequency oscillation and centroid frequency of diaphragm EMG during inspiratory loading

Exposure of progenitor cells with chondrogenic potential to recombinant human osteogenic protein-1 [rhOP-1, or bone morphogenetic protein-7 (BMP-7] may be of therapeutic interest in the regeneration of articular cartilage. Therefore, in this study, we examined the influence of rhOP-1 on cartilage formation by human perichondrium tissue containing progenitor cells with chondrogenic potential in vitro. Fragments of outer ear perichondrium tissue were embedded in clotting autologous blood to which rhOP-1 had been added or not (controls), and the resulting explant was cultured for 3 weeks without further addition of rhOP-1. Cartilage formation was monitored biochemically by measuring [³5;S]sulfate incorporation into proteoglycans and histologically by monitoring the presence of metachromatic matrix with cells in nests. The presence of rhOP-1 in the explant at the beginning of culture stimulated [³5;S]sulfate incorporation into proteoglycans in a dose-dependent manner after 3 weeks of culture. Maximal stimulation was reached at 40 microgram/ml. Histology revealed that explants treated with 20-200 microgram/ml rhOP-1, but not untreated control explants, contained areas of metachromatic-staining matrix with chondrocytes in cell nests. These results suggest that rhOP-1 stimulates differentiation of cartilage from perichondrium tissue. The direct actions of rhOP-1 on perichondrium cells to stimulate chondrocytic differentiation and production of cartilage matrix in vitro provide a cellular mechanism for the induction of cartilage formation by rhOP-1 in vivo. Thus, rhOP-1 may promote early steps in the cascade of events leading to cartilage formation. Therefore, rhOP-1 could be an interesting factor for regeneration of cartilage in articular cartilage defects.     

Salivary cortisol and cardiovascular activity during stress in oppositional-defiant disorder boys and normal controls

The erythroleukemic cell line K562 can undergo further differentiation in erythroid or megakaryocytic lineage depending on the nature of the stimulus. Phorbol ester (PMA) stimulates megakaryocytic development whereas hemin promotes erythroid differentiation of these cells. We have examined the effect of PMA and hemin on the expression of the Kell blood group and CD10 antigens, two related proteins that belong to a family of membrane-bound neutral metalloendopeptidases. We show here that differentiation of K562 cells by PMA in the megakaryocytic lineage results in abolishment of Kell mRNA accumulation and protein expression and, in parallel, the induction of CD10 mRNA accumulation, protein expression, and enzymatic activity. Conversely, differentiation of these cells by hemin in the erythroid lineage is accompanied by an up-regulation of Kell mRNA and protein expression, with no changes in CD10 mRNA and protein expression. Thus, CD10 and Kell can be regarded as specific markers of the differentiation of K562 cells in the megakaryocytic and erythroid lineages, respectively.     

Occupational role stress in the Canadian forces: Its association with individual and organizational well-being.

Studies on workplace stress have been conducted in various occupational environments. However, published reports exploring occupational stress in the military are rare. This study examines occupational stress in the Canadian Forces within the framework of social role theory and its relation to employee health, job satisfaction, and organizational commitment. Ss were 1,068 Regular Forces military members who completed a survey questionnaire. Of interest were the psychological resources (e.g., individual coping skills, workplace leadership, and perceived organizational support) that have the potential to alter the perception of work stress and/or alleviate its association with individual and organizational outcomes. Regression analyses indicated a negative association between occupational role stress and both individual (strain) and organizational (job satisfaction and organizational commitment) well-being. No moderating effects were found for coping strategies, workplace leadership, or perceived organizational support, although these factors had direct relationships with both individual and organizational well-being The results are discussed in terms of the potential of organizational resources and role stress to cascade across organizational levels. (PsycINFO Database Record (c) 2010 APA, all rights reserved)