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PubMed1987

Fast voluntary trunk flexion movements in standing: motor patterns.

The electromyographical (EMG) activity was studied during voluntary flexion movements of the trunk in erect standing man. The movements were performed at maximal velocity with successively increasing amplitude to cover the whole range of motion. The EMG activity was recorded from agonist-antagonist pairs of muscles at the ankle, knee, hip and trunk. The angular displacements at the corresponding joints were recorded using a Selspot optoelectronic system. The duration of initiating activity in prime movers (rectus abdominis and rectus femoris) as well as time to onset of activity in muscles braking the primary movement (erector spinae, gluteus maximus and hamstrings) were highly correlated with amplitude, duration, peak velocity and time to peak velocity of the movement (r = 0.59-0.91). The corresponding correlations for peak acceleration and deceleration of the movement were low (r = 0.03-0.38), indicating that acceleration and deceleration of a movement was not coded in the temporal aspects of the EMG. Onset of activity in rectus abdominis and rectus femoris as well as an early appearing burst of activity in vastus lateralis were invariant in relation to start of movement over the whole movement range. In the initial phase of a fast trunk flexion, activity in tibialis anterior appeared successively earlier with increasing movement amplitude. This resulted in a changed order of activation for the muscles from proximal to distal (rectus abdominis first) to distal to proximal (tibialis anterior first). Two different forms of associated postural adjustments are present during a fast trunk flexion, one early fast knee flexion and a later slower angle extension. Prior to knee flexion, no activity was recorded from muscles flexing at the knee implying that some other force must create a flexing torque around the knee. It is suggested that activity in rectus abdominis initiating the primary movement also initiates knee flexion through the upward pulling of pelvis. This would be possible since rectus femoris stabilizes the pelvis in relation to the leg, allowing the force in rectus abdominis to be transmitted below the hip joint and act extending around the ankle joint. However, when tibialis anterior is activated it stabilizes the shank which in turn will cause a knee flexion controlled by a lengthening contraction in vastus lateralis. During the subsequent ankle extension activity appears in lateral gastrocnemius and soleus causing the associated postural adjustment at the ankle. It can be concluded that activation of postural muscles prior to prime mover muscles is not always necessary.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1987

Adaptations to changing speed in human locomotion: speed of transition between walking and running.

The transition speed between walking and running was determined in 18 healthy males (23-38 years) of various statures (range of leg length 0.86-1.09 m) during acceleration and deceleration of different magnitudes (0.05-0.11 ms-2) on a motor-driven treadmill. The speed of the treadmill belt and the duration of the stance phases of each foot were recorded. A transition step was identified and the speed of transition was taken as the average speed value of the stance phase of that step. The overall mean value for the transition speed was 1.88 m s-1 (range 1.30-2.55). Deceleration resulted in a somewhat lower speed of transition than acceleration. There was a tendency towards increasing values for transition speed with increasing leg length. This could partly be explained by differences in natural frequency. The reasons for the switch between walking and running at a speed which is not extreme for either mode of progression are unclear. The subjective feeling that a transition will lead to a more comfortable situation might be based on previous experience combined with information from peripheral receptors and activity in central networks controlling locomotion.

Adult↗
PubMed1995

Metabolic and mechanical aspects of foot landing type, forefoot and rearfoot strike, in human running.

The study was undertaken to assess the metabolic and the mechanical aspects of two different foot strike patterns in running, i.e. forefoot and rearfoot striking (FFS and RFS), and to understand whether there is some advantage for a runner to use one or the other of the two landing styles. Eight subjects performed two series of runs (FFS and RFS) on a treadmill at an average speed of 2.50, 2.78, 3.06, 3.33, 3.61, 3.89, 4.17 m s-1. Step frequency, oxygen uptake, mechanical work, and its two components, external and internal, were measured. No differences were found for step frequency, mechanical internal work per unit time and oxygen uptake, while external and total mechanical work per unit time were significantly higher, 7-12%, for FFS. The higher external work was the result of an increase of the work performed against both gravitational and inertial forces. As the energy expenditure was the same it has been speculated that a higher storage and release of energy takes place in the elastic structures of the lower leg with FFS. In a different series of experiments on six subjects contact time, time of deceleration and time of acceleration were measured by means of a video camera while running on the treadmill at 2.50, 3.33 and 4.17 m s-1, both FFS and RFS. Time of deceleration is similar for FFS and RFS, but contact time and time of acceleration are shorter, respectively 12 and 25%, for FFS.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1998

Measurement of cardiac function by transthoracic echocardiography: day to day variability and repeatability in normal Thoroughbred horses.

In order to assess the reliability and repeatability of transthoracic echocardiography for detecting serial changes in cardiac function in horses, day to day variability of a number of echocardiographic indices of ventricular function were studied. The variables investigated were, from 2-dimensional (2-D) and M-mode echocardiography - aortic diameter in systole (Aos), pulmonary artery diameter in systole (Pas), left ventricular internal diameter in systole (LLVIDs) and diastole (LLVIDd), and left ventricular fractional shortening (%FS) and estimated ejection fraction (EF). From pulsed Doppler echocardiography - maximum velocity (Vmax) and acceleration (dv/dtmax) of aortic and pulmonary arterial blood flow, left and right ventricular velocity time integral (AoVTI and PAVTI) and estimated cardiac output (COLV, and CORV), left and right ventricular ejection time (LVET and RVET) and pre-ejection period (LVPEP and RVPEP), and heart rate. Maximum velocity of early rapid right ventricular filling (ETV) and late right ventricular filling due to right atrial contraction (ATV) were measured. Maximum deceleration and time for deceleration of early rapid filling (dv/dtTV and dt TV) were also determined. Seven healthy mature Thoroughbred horses weighing 490-600 kg were studied. The horses' management regimes and environment were standardised and an echocardiographic examination was carried out on each horse at the same time every day for 6 consecutive days. Two statistical measures of repeatability were calculated for each variable: the intraclass correlation coefficient (rI) and the 95% confidence intervals for error free value of a single measurement. In general, the dimensions and indices of cardiac function derived from 2-D and M-mode echocardiography showed better repeatability for individual horses than did the indices derived from Doppler echocardiography. Overall the 95% confidence intervals for an error-free value of all variables derived from Doppler echocardiography were wide. This must be appreciated when attributing serial measured changes of Doppler echocardiographic variables in an individual animal to effects of a treatment or disease.

Analysis of Variance↗
PubMed1970

Persistence of the cardio-inhibitory response to brain stem ischaemia after destruction of the area postrema and the dorsal vagal nuclei.

1. In anaesthetized cats, in which the carotid arterial bifurcation had been denervated and the spinal cord transected at the cervical level, reversible bradycardia mediated by the vagus nerves was elicited by temporary arrest of the cranial circulation. Methoxamine was infused intravenously to maintain peripheral vascular resistance, and artificial ventilation was given to avert systemic asphyxia.2. The bradycardia persisted in cats subjected to one or more of the following acute surgical procedures: left vagotomy, mid-collicular decerebration, decerebellation, bulbar transections at the acoustic striae and inferior fovea, and destruction of the area postrema and the underlying dorsal vagal nuclei. Ischaemia-induced bradycardia was invariably abolished after bilateral vagotomy or the administration of atropine.3. Bradycardia could not be elicited by electrical stimulation of the dorsal vagal nuclei, but was evoked by stimulation of deep structures in the vicinity of the nucleus ambiguus even after destruction of the dorsal vagal nuclei.4. Simultaneous application of ischaemia and electrical stimulation of the medullary cardio-decelerator locus produced convergent occlusion of the vagal response. The effect of ischaemia was inhibited by stimulation of a neighbouring region in the medial reticular formation. These interactions indicate that an interneuronal link is involved in the mechanism of ischaemia-induced bradycardia.5. It is concluded that the cardio-decelerator response to ischaemia is initiated upstream to the primary efferent vagal motor neurones and that the cardio-inhibitory fibres do not originate in the dorsal vagal nuclei.

Animals↗
PubMed1984

Corrective reactions to stumbling in man: neuronal co-ordination of bilateral leg muscle activity during gait.

Electromyogram (e.m.g.) responses of lower leg muscles, and corresponding movements were studied following a perturbation of the limb during walking, produced by either (a) a randomly timed, short acceleration or decelerating impulse applied to the treadmill, or (b) a unilateral triceps surae contraction induced by tibial nerve stimulation. Bilateral e.m.g. responses following the perturbation were specific for the mode of perturbation and depended on the phase of the gait cycle in which the perturbation occurred. Treadmill deceleration evoked a bilateral tibialis anterior activation; acceleration evoked an ipsilateral gastrocnemius and contralateral tibialis anterior activation (latency in either condition and on both sides was 65-75 ms, duration about 150 ms). Tibial nerve stimulation at the beginning of a stance phase, was followed by an ipsilateral tibialis anterior activation; during the swing phase it was followed by an ipsilateral tibialis anterior and contralateral gastrocnemius activation (latency about 90 ms, duration about 100 ms). These patterns differed from the response seen after a unilateral displacement during static standing, which evoked a bilateral tibialis anterior activation. These early responses were in most cases followed by late ipsilateral responses, but the e.m.g. pattern of the next step cycle was usually unchanged, or affected only at its onset. The e.m.g. responses were unaltered by ischaemic nerve blockade of group I afferents, by training effects or by pre-warning of the onset of perturbation (randomly or self-induced). Despite the different e.m.g. responses following a perturbation during gait, the same basic functional mechanism was obviously at work: the early ipsilateral response achieved a repositioning of the displaced foot and leg, while the early contralateral and late ipsilateral responses provided compensation for body displacement. It is suggested that the e.m.g. responses may be mediated predominantly by peripheral information from group II and group III afferents, which modulate the basic motor pattern of spinal interneuronal circuits underlying the respective motor task.

Adult↗
PubMed1995

Modeling and simulation of paraplegic ambulation in a reciprocating gait orthosis.

We developed a three dimensional, four segment, eight-degree-of-freedom model for the analysis of paraplegic ambulation in a reciprocating gait orthosis (RGO). Model development was guided by experimental analysis of a spinal cord injured individual walking in an RGO with the additional assistance of arm crutches. Body forces and torques required to produce a dynamic simulation of the RGO gait swing phase were found by solving an optimal control problem to track the recorded kinematics and ground reaction forces. We found that high upper body forces are required, not only during swing but probably also during double support to compensate for the deceleration of the body during swing, which is due to the pelvic thrust necessary to swing the leg forward. Other stimulations showed that upper body forces and body deceleration during swing can be reduced substantially by producing a ballistic swing. Functional neuromuscular stimulation of the hip musculature during double support would then be required, however, to establish the initial conditions needed in a ballistic swing.

Biomechanical Phenomena↗
PubMed2001

Vortex sound generation due to a flow impedance discontinuity on a flat surface.

The sound generated by the unsteady motion of a vortex filament moving over a flat boundary with a sharp flow impedance discontinuity is studied theoretically. Theoretical results show that the vortex filament undergoes significant accelerating or decelerating motions and radiates sound at the instant when it moves across the plane of impedance discontinuity. The accelerations and decelerations of the vortex filament are shown to be the major mechanisms of sound generation. The sound so produced has a large low-frequency content such that the change in the flow impedance affects only the sound generation process but not the subsequent sound propagation to the far field.

Journal Article↗
PubMed2002

Symmetry of discrete and oscillatory elbow movements: does it depend on torque that the agonist and antagonist muscle can exert?

The hypothesis that strength of active muscles affects the symmetry of the velocity profiles of voluntary movements was tested. In particular, it was assumed that the duration of acceleration and deceleration phases reflects the ability of the antagonistic muscles to exert torque in such a way that stronger muscle requires less time for action. Twelve subjects performed consecutive 50 flexions and extensions in blocks of either discrete or oscillatory movements. They were tested under high and moderate speed conditions, as well as within different ranges of elbow joint angles. The symmetry ratio (SR; acceleration time divided by deceleration time) was calculated in order to assess movement symmetry. The results demonstrated SR > 1 under most of the discrete and, particularly, oscillatory movement conditions. A velocity-associated increase in SR was recorded, while different ranges of elbow movements, assumed to provide different torques of the agonist and antagonist muscles, also provided different SR. The findings were generally in line with the predicted effects of movement conditions on muscle strength, particularly those related to elbow angle and elbow angular velocity. Deviations from the ideal movement symmetricity have usually been interpreted as either weakness of various motor control models and hypotheses, or as a sub-optimal control of movements in certain subject populations; the present study suggests an alternative interpretation based upon the ability of active muscles to exert torque

Adult↗
PubMed2003

Effects of target height and width on 2D pointing movement duration and kinematics.

This study examined the impact of target geometry on the trajectories of rapid pointing movements. Participants performed a graphic point-to-point task using a pen on a digitizer tablet with targets and real time trajectories displayed on a computer screen. Circular- and elliptical-shaped targets were used in order to systematically vary the accuracy constraints along two dimensions. Consistent with Fitts Law, movement time increased as target difficulty increased. Analysis of movement kinematics revealed different patterns for targets constrained by height (H) and width (W). When W was the constraining factor, movements of greater precision were characterized by a lower peak velocity and a longer deceleration phase, with trajectories that were aimed relatively farther away from the center of the target and were more variable across trials. This indicates an emphasis on reactive, sensory-based control. When H was the constraining factor, however, movements of greater precision were characterized by a longer acceleration phase, a lower peak velocity, and a longer deceleration phase. The initial trajectory was aimed closer to the center of the target, and the trajectory path across trials was more constrained. This suggests a greater reliance on both predictive and reactive control.

Acceleration↗
PubMed2004

The control of memory-guided reaching movements in peripersonal space.

The goal of the present investigation was to explore the putative contributions of feedforward- and feedback-based processes in the control of memory-guided reaching movements. Participants (N = 4) completed an extensive number of reaching movements (2700) to 3 midline targets (20, 30, 40 cm) in 6 visual conditions: full-vision, open-loop, and four memory-guided conditions (0, 200, 400, and 600 ms of delay). To infer limb control, we used a regression technique to examine the within-trial correspondence between the spatial position of the limb at peak acceleration, peak velocity, peak deceleration, and the ultimate movement endpoint. A high degree of within-trial correspondence would suggest that the final position of the limb was largely specified prior to movement onset and not adjusted during the action (i.e., feedforward control); conversely, a low degree of within-trial correspondence would suggest that movements were modified during the reaching trajectory (i.e., feedback control). Full-vision reaches were found to be more accurate and less variable than open-loop and memory-guided reaches. Moreover, full-vision reaches demonstrated only modest within-trial correspondence between the spatial position of the limb at each kinematic marker and the ultimate movement endpoint, suggesting that reaching accuracy was achieved by adjusting the limb trajectory throughout the course of the action. Open-loop and memory-guided movements exhibited strong within-trial correspondence between final limb position and the position of the limb at peak velocity and peak deceleration. This strong correspondence indicates that the final position of the limb was largely determined by processes that occurred before the reach was initiated; errors in the planning process were not corrected during the course of the action. Thus, and contrary to our previous findings in a video-based aiming task, it appears that stored target information is not extensively (if at all) used to modify the trajectory of reaching movements to remembered targets in peripersonal space.

Adult↗
PubMed1974

Gross map distances and Hfr transfer times in Escherichia coli K-12.

Hfr strains B4 and B8 transfer the Escherichia coli chromosome in opposite directions, each transferring lac(+) as the last known marker. They were mated in concurrent crosses with the proA leu metE lys trp purE lac strain chi462. Analysis of the time of entry values for these markers showed that Hfr strain B8 transfers the whole chromosome more rapidly than does Hfr strain B4. In both crosses, the rate of transfer observed decelerates. If deceleration occurs as a function of the amount of chromosome transferred, the data are consistent with the markers examined being very accurately placed on the Taylor-Trotter map of the E. coli K-12 genome.

Chromosome Mapping↗
PubMed2004

Transcriptional regulation of Vibrio cholerae hemagglutinin/protease by the cyclic AMP receptor protein and RpoS.

Vibrio cholerae secretes a Zn-dependent metalloprotease, hemagglutinin/protease (HA/protease), which is encoded by hapA and displays a broad range of potentially pathogenic activities. Production of HA/protease requires transcriptional activation by the quorum-sensing regulator HapR. In this study we demonstrate that transcription of hapA is growth phase dependent and specifically activated in the deceleration and stationary growth phases. Addition of glucose in these phases repressed hapA transcription by inducing V. cholerae to resume exponential growth, which in turn diminished the expression of a rpoS-lacZ transcriptional fusion. Contrary to a previous observation, we demonstrate that transcription of hapA requires the rpoS-encoded sigma(s) factor. The cyclic AMP (cAMP) receptor protein (CRP) strongly enhanced hapA transcription in the deceleration phase. Analysis of rpoS and hapR mRNA in isogenic CRP+ and CRP- strains suggested that CRP enhances the transcription of rpoS and hapR. Analysis of strains containing hapR-lacZ and hapA-lacZ fusions confirmed that hapA is transcribed in response to concurrent quorum-sensing and nutrient limitation stimuli. Mutations inactivating the stringent response regulator RelA and the HapR-controlled AphA regulator did not affect HA/protease expression. Electrophoretic mobility shift experiments showed that pure cAMP-CRP and HapR alone do not bind the hapA promoter. This result suggests that HapR activation of hapA differs from its interaction with the aphA promoter and could involve additional factors.

Bacterial Proteins↗
PubMed2003

Borna disease virus nucleoprotein interacts with the CDC2-cyclin B1 complex.

Transition from G(2) to M phase, a cell cycle checkpoint, is regulated by the Cdc2-cyclin B1 complex. Here, we report that persistent infection with Borna disease virus (BDV), a noncytolytic RNA virus infecting the central nervous system, results in decelerated proliferation of infected host cells due to a delayed G(2)-to-M transition. Persistent BDV-infected rat fibroblast cells showed reduced proliferation compared to uninfected cells. In pull-down assays we observed an interaction of the viral nucleoprotein with the Cdc2-cyclin B1 complex. Transfection of the viral nucleoprotein but not of the phosphoprotein also results in decelerated proliferation. This phenomenon was found in BDV-susceptible primary rat fibroblast cells and also in primary mouse cells, which are not susceptible to BDV infection. This is the first evidence that the noncytolytic Borna disease virus can manipulate host cell functions via interaction of the viral nucleoprotein with mitotic entry regulators. BDV preferentially infects and persists in nondividing neurons. The present report could give an explanation for this selective choice of host cell by BDV.

Animals↗
PubMed1995

A trinucleotide repeat-associated increase in the level of Alu RNA-binding protein occurred during the same period as the major Alu amplification that accompanied anthropoid evolution.

Nearly 1 million Alu elements in human DNA were inserted by an RNA-mediated retroposition-amplification process that clearly decelerated about 30 million years ago. Since then, Alu sequences have proliferated at a lower rate, including within the human genome, in which Alu mobility continues to generate genetic variability. Initially derived from 7SL RNA of the signal recognition particle (SRP), Alu became a dominant retroposon while retaining secondary structures found in 7SL RNA. We previously identified a human Alu RNA-binding protein as a homolog of the 14-kDa Alu-specific protein of SRP and have shown that its expression is associated with accumulation of 3'-processed Alu RNA. Here, we show that in early anthropoids, the gene encoding SRP14 Alu RNA-binding protein was duplicated and that SRP14-homologous sequences currently reside on different human chromosomes. In anthropoids, the active SRP14 gene acquired a GCA trinucleotide repeat in its 3'-coding region that produces SRP14 polypeptides with extended C-terminal tails. A C-->G substitution in this region converted the mouse sequence CCA GCA to GCA GCA in prosimians, which presumably predisposed this locus to GCA expansion in anthropoids and provides a model for other triplet expansions. Moreover, the presence of the trinucleotide repeat in SRP14 DNA and the corresponding C-terminal tail in SRP14 are associated with a significant increase in SRP14 polypeptide and Alu RNA-binding activity. These genetic events occurred during the period in which an acceleration in Alu retroposition was followed by a sharp deceleration, suggesting that Alu repeats coevolved with C-terminal variants of SRP14 in higher primates.

Animals↗
PubMed2006

Specific features of changes in levels of endogenous respiration substrates in Saccharomyces cerevisiae cells at low temperature.

The rate of endogenous respiration of Saccharomyces cerevisiae cells incubated at 0 degrees C under aerobic conditions in the absence of exogenous substrates decreased exponentially with a half-period of about 5 h when measured at 30 degrees C. This was associated with an indirectly shown decrease in the level of oxaloacetate in the mitochondria in situ. The initial concentration of oxaloacetate significantly decreased the activity of succinate dehydrogenase. The rate of cell respiration in the presence of acetate and other exogenous substrates producing acetyl-CoA in mitochondria also decreased, whereas the respiration rate on succinate increased. These changes were accompanied by an at least threefold increase in the L-malate concentration in the cells within 24 h. It is suggested that the increase in the L-malate level in the cells and the concurrent decrease in the oxaloacetate level in the mitochondria should be associated with a deceleration at 0 degrees C of the transport of endogenous respiration substrates from the cytosol into the mitochondria. This deceleration is likely to be caused by a high Arrhenius activation energy specific for transporters. The physiological significance of L-malate in regulation of the S. cerevisiae cell respiration is discussed.

Aerobiosis↗
PubMed1986

Growth and childhood asthma.

Height and weight were measured every six months in a long term prospective study of 66 children with chronic perennial asthma for a mean 13.1 years. There was no evidence of growth retardation on entry into the study. Growth developed along normal lines in all 66 children until about 10 years, and in 35 of these children growth continued along normal lines throughout the whole period of follow up. Thirty children showed the physiological decelerating growth velocity pattern seen in children with delay in the onset of puberty, and one child had an early menarche. The tendency for delay in the onset of puberty was significant for both boys and girls and was noted to be independent of severity of asthma. Once puberty finally began in these children, complete catch up growth resulted in the attainment of the predicted adult height. Long term prophylactic inhalation of beclomethasone dipropionate in 26 children in a dosage up to 600 mcg/day before puberty and 400 mcg/day during puberty was shown not to affect growth. It is concluded that asthma had no direct influence on growth in height but was associated with delay in the onset of puberty. The pre-adolescent physiological deceleration of growth velocity that occurs in these children gives the impression of growth retardation.

Asthma↗
PubMed2001

Spontaneous reversal of nystagmus in the dark.

AIM: To report five children with horizontal jerk nystagmus in whom eye movement recordings in the dark revealed a spontaneous reversal in the direction of the nystagmus beat. Three patients were blind in one eye and were diagnosed as having a manifest latent nystagmus (MLN), and two patients had strabismus and congenital nystagmus (CN). METHODS: Eye movements were recorded using DC electro-oculography with simultaneous video recording, including infrared recording in total darkness. RESULTS: Four patients had decelerating velocity slow phase jerk nystagmus when recorded under natural lighting conditions; the fifth case had accelerating velocity and linear slow phase jerk nystagmus. Under absolute darkness, nystagmus reversed in direction of beat with a mixture of linear and decelerating velocity slow phase waveforms. One child with unilateral anophthalmos could wilfully reverse the beat direction of his nystagmus by trying to look with his blind eye in the light and dark. CONCLUSIONS: These observations support the theory that LN/MLN beat direction is determined by the "presumed" viewing eye and may be consciously controlled. The spontaneous reversal of beat direction in the dark suggests eye dominance is predetermined. Eye movement recordings identified mixed nystagmus waveforms indicating that CN (accelerating velocity slow phases) and LN/MLN (linear/decelerating velocity slow phases) coexist in these subjects.

Anophthalmos↗