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At least 541 records · Page 30Linked to original sources
PubMed1990

Changes in stature following drop jumping and post-exercise gravity inversion.

Spinal shrinkage, measured by changes in stature, is used as an index of spinal loading as alterations reflect changes in intervertebral disc height. Shrinkage induced by various physical activities may be reversed using gravity inversion. The present purpose was to examine the shrinkage induced by a drop jumping regimen and evaluate gravity inversion post-exercise. Eight males, aged 20-31, performed two separate experimental protocols, each on different dates at 1400 h. Subjects stood for 30 min before undertaking an exercise regimen, consisting of five sets of five drop jumps from a height of 1 m, rebounding over a hurdle 0.5 m high. For 20 min, directly following the exercise regimen, subjects on one occasion stood and on a second occasion undertook gravity inversion. Shrinkage was monitored for 40 min after this post-exercise treatment. The stadiometer used to measure shrinkage was accurate to 0.05 mm. The exercise regimen caused a mean shrinkage of 1.68 and 1.81 mm for the two testing sessions. Post-exercise inversion and standing for 20 min increased stature by 5.18 and 0.76 mm, respectively (P less than 0.01). The 40-min standing period following inversion caused a rapid loss in stature (4.07 mm). At 30 min into this recovery period, there was no significant difference in shrinkage for either of the regimens. Results suggest that effects of an inversion treatment are short-lasting.

Adult↗
PubMed1989

Correction for gravity in isokinetic dynamometry of knee extensors in below knee amputees.

In isokinetic dynamometry of the knee extensors the influence of gravity on the lower limb is often neglected. The aim of this study was to assess the shape, the quantity and reproducibility of the gravity correction curve (GCC). Eight amputees participated in this study. The GCC was produced on an isokinetic dynamometer (QD) throughout the range of motion on the amputated side with prosthesis and on the non-amputated side. The results were compared with the GCC calculated according to the Cybex data reduction computer procedure. The isokinetic torque registration of the QD is, in a mathematical way, a straight line (Pearson correlation coefficient greater than 0.99). The other GCC is shaped like a cosinus curve. The intra-individual reproducibility is high, the inter-individual variability substantial. An explanation for the difference between the two methods is discussed. For an ideal measurement of the muscular torque, one should not only correct for the effect of gravity but for all factors counteracting the effect of the knee extensors. In that case an individual GCC should be made directly with the dynamometer.

Adolescent↗
PubMed1989

[Analysis of "rising up mechanism" in months-old infants--determination of contact area and center of gravity by pedoscope].

The author studied how the rising up mechanism changed with the development of motor function in healthy infants. 1. The rising up mechanism can be evaluated from the body support pattern characteristic to each stage of posture development in supine and prone positions, the body support (contact) area and shift in the center of gravity. 2. The support patterns in supine position were classified into 4 types; S-I ("squid type", 2-4 mo), S-II ("platform type", 4-6 mo), S-III ("bell type", 7-10 mo), S-IV ("separate type"), and their characteristics were described. 3. The contact area in supine position gradually decreased as the support pattern changed from S-I (area ratio, approx. 2/3) to S-III (area ratio, 2/5). 4. The center of gravity in supine position was located at 10th thoracic vertebra at 2-4 mo, then rose with age until it was stabilized at 7th thoracic vertebra at 10 mo. 5. The support patterns in prone position were classified into 7 types; P-I ("protector type", 2-3 mo), P-II ("joint square and round type", 3-4 mo), P-III ("elongated oval type", 4 mo-first half of 5 mo), P-IV ("spindle type", 4 mo-latter half of 5 mo), P-V ("ginseng type", 5-6 mo), P-VI ("tetrapod type", 7-10 mo), P-VII ("oval type", 9 mo onward), and their characteristics were described. 6. The contact area in prone position gradually increased as the support pattern changed from P-I (area ratio, 3/5) to P-V (area ratio, 9/slightly over 10), and gradually decreased as it changed thereafter to P-VII (area ratio, 7/slightly under 10). 7. The center of gravity in prone position swung over a wide range. It was located at 12th thoracic vertebra at 2-3 mo, then ascended as far as 9th thoracic vertebra at 4 mo-first half of 5 mo, and descended thereafter to be stabilized at 2nd lumbar vertebra (level of navel) at around 10 mo. 8. Particular attention was paid to the development of rising up mechanism in the upper extremities in observation of changes in the support pattern.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMedDate not supplied

Peristalsis in pharyngeal constrictor musculature in relation to positioning and gravity.

The motor activity of the pharyngeal constrictors in terms of peristalsis and protrusion depths was studied cineradiographically in 15 non-dysphagic volunteers in three positions: sitting, right decubitus horizontal, and head-down 30 degrees, during swallowing of a 10 ml bolus of thin liquid barium. Using a frame rate of 50/s the speed of peristalsis was calculated by frame counting. The speed of peristalsis and the depth of protrusion of the constrictor wall did not depend on the direction of gravity force in relation to the long axis of the pharynx. Neither the position of the hyoid bone nor its movement during pharyngeal swallowing changed in relation to position and gravity. Pharyngeal activity during swallowing in normal individuals is fairly stable and does not change in relation to gravity.

Adult↗
PubMed1987

Observations with SPECT on the normal regional distribution of pulmonary blood flow in gravity independent planes.

While the effect of gravity on the pulmonary circulation is well documented, the distribution of pulmonary flow under gravity independent conditions is not as well understood. Single photon emission computed tomography was applied to the study of regional pulmonary blood flow in slices where the effect of gravity was constant. Lung tomography, after the injection of [99mTc]MAA, was carried out in six normal volunteers and in the fully inflated and isolated lungs from six dogs that had been killed. Our tomographic results suggest that pulmonary perfusion in isogravitational planes is inherently nonuniform with preferential flow centrally and reduced circulation more peripherally. Planar imaging of the dissected isogravitational slices from the animals further confirmed the uneven perfusion noted on the tomographic slices.

Adult↗
PubMed1985

In vivo accuracy of gravity-flow i.v. infusion systems.

The accuracy of fluid delivery via gravity-flow i.v. infusion systems in hospitalized patients was evaluated. All adult patients on the medical-surgical wards of a university hospital who were receiving i.v. fluids via gravity-flow infusion sets were studied during a four-day period. Data collected approximately every two hours over a 15-hour period daily included the prescribed i.v. flow rate, type of i.v. set (microdrop or macrodrop), drop rate, and the approximate volume of fluid remaining in the i.v. container. Drop rates were measured with a photocell device placed around the drip chamber of the i.v. set. A total of 509 observations involving 86 patients were recorded during the study; drop rates were evaluated at flow rates for which there were 20 or more observations. For the majority of flow rates and set types, less than 15% of observations were within +/- 10% of desired drop rates, while only 21% of observations fell within +/- 20% of desired drop rates. Mean versus desired volume of fluid delivered between observations differed substantially but not as much as anticipated based on drop rate variability, reflecting nurses' attempt to adjust fluid therapy based on volume of fluid delivered. Intravenous fluid delivery via gravity-flow i.v. infusion systems is highly inaccurate. To ensure appropriate fluid delivery, better monitoring or improvement of i.v. fluid administration systems or the use of electronic infusion control devices is recommended.

Equipment and Supplies, Hospital↗
PubMed1985

Motion of the center of gravity of the body in clinical evaluation of gait.

The motion of the center of gravity during walking was analyzed in five hemiplegic subjects and eleven subjects affected by unilateral hip arthritis. In the hemiplegic subjects and 6 subjects with hip arthritis the transfer between kinetic and potential energy (with a passive pendular motion) was found to be 9-95% greater during the step performed on the affected limb ("pathological" step); as a consequence, the muscular work done during this step was 7-81% of the work done during the step performed on the second limb ("normal" step). Qualitatively similar gait anomalies were recorded in all hemiplegic subjects with hypertonus of the paretic limb: these subjects had to lift the spastic limb as a whole during the normal step, with the consequence that the center of gravity was lifted 0.6-3 cm more than during the pathological step. In contrast, various motor patterns were found in patients with hip arthritis. During the pathological step the center of gravity reached a height 0.5-3 cm greater in 7 subjects, 1 cm smaller in one subject, and about the same height reached during the normal step in 3 subjects. This was consistent with the various motor deficits caused by hip arthritis.

Aged↗
PubMed1983

Neck muscle loading and fatigue: systematic variation of headgear weight and center-of-gravity.

An extensive series of experiments has been conducted to quantify the fatigue of neck muscles as measured by isometric endurance time. The neck muscles were dynamically and statically loaded by systematic variation of 15 headgear configurations consisting of 5 different centers-of-gravity (forward-low, center-low, center-high, right-lateral-low and afterward-low) and 3 different weights (3.2 lb, 5.0 lb, 9.0 lb, 1.45, 2.27, 4.09 kg). Each of six subjects would rotate his head laterally (from side-to-side) for 30 min in each of the 15 headgear loading combinations. Immediately thereafter, the subject would position his head in an isometric head dynamometer and exert a sustained right lateral neck contraction at 70% of his maximum strength (MVC), during which endurance time (to fatigue) was recorded. The results indicate that there were no significant differences (p greater than 0.05) in endurance time between the 3.2 lb/forward-low, 3.2 lb/lateral-right-low, and 9.0 lb/afterward-low compared to controls (endurance time for at 70% MVC isometric neck contraction in which there was no prior head loading). All other head loading configurations (weight and center-of-gravity combinations) did result in a significant reduction (p less than or equal to 0.05) in endurance times (compared to controls). These results are significant since they provide useful insights into the optimal trade-off between various centers-of-gravity and helmet weight combinations which result in the optimization of neck muscle endurance.

Adult↗
PubMedDate not supplied

Body orientation and regulation of the center of gravity during movement under water.

Professional divers were instructed to adopt a vertical posture under water with their feet fixed to the ground and to perform a fast forward or backward upper trunk bending movement in response to a tone. Kinematic and EMG analyses were performed. It was first noted that the divers adopted a forward inclined, erect posture, suggesting that the verticality was misevaluated, although the effects of gravity were still exerted on the otoliths. Second, the upper trunk movements were still accompanied by opposite movements of lower segments and, as a result, the center of gravity displacement was still minimized, although not so accurately as on the ground. The EMG pattern consisting of early activation of a set of trunk, thigh, and shank muscles continued to occur under water. These results suggest that "axial synergies" associated with upper trunk movements are learned motor habits that regulate the center of gravity position regardless of the equilibrium constraints.

Adaptation, Physiological↗
PubMedDate not supplied

[Medical and biological aspects of artificial gravity: animal studies].

In the review there analyzed the results of ground-based studies of rotation effects (at a gravity value near 1 g) on the animals, the experimental findings to determine a minimum effective value of artificial gravity as well as the data of biosatellite experiments. The major trends of animal studies in the artificial gravity area is presented.

Adaptation, Physiological↗
PubMed1993

A multidimensional model of the effect of gravity on the spatial orientation of the monkey.

A "sensory conflict" model of spatial orientation was developed. This mathematical model was based on concepts derived from observer theory, optimal observer theory, and the mathematical properties of coordinate rotations. The primary hypothesis is that the central nervous system of the squirrel monkey incorporates information about body dynamics and sensory dynamics to develop an internal model. The output of this central model (expected sensory afference) is compared to the actual sensory afference, with the difference defined as "sensory conflict." The sensory conflict information is, in turn, used to drive central estimates of angular velocity ("velocity storage"), gravity ("gravity storage"), and linear acceleration ("acceleration storage") toward more accurate values. The model successfully predicts "velocity storage" during rotation about an earth-vertical axis. The model also successfully predicts that the time constant of the horizontal vestibulo-ocular reflex is reduced and that the axis of eye rotation shifts toward alignment with gravity following postrotatory tilt. Finally, the model predicts the bias, modulation, and decay components that have been observed during off-vertical axis rotations (OVAR).

Animals↗
PubMed1995

[Biomechanical aspects of the process of formation of food vacuoles in the infusoria Bursaria truncatella under changed gravity].

Results from clinostatic and centrifugal laboratory experiments in which there has been evaluated an activity of digestive process in infusoria Bursaria truncatella by the content of vacuole numbers and its change in the cell under changed gravity are presented. It is indicated that the extended clinostatic exposure of infusoria stimulates their digestive activity and an increased gravity (centrifugation 2 g, 5 g) inhibits this process. In these examinations, an effort was made to explain the obtained results started from the propositions of cell biomechanics and bioenergetics. The mechanisms of gravity influence on this process have been proposed.

Animals↗
PubMed1995

[Venous leakage impotence: anatomical and physiological considerations upon gravity cavernosometry and radio-fluorographic cavernosography].

We performed gravity cavernosometry and radio-fluoro-graphic cavernosography with pharmacological intracavernous injection in 15 patients with erectile dysfunction. On the basis of cavernosographyc findings, in the 15 patients leak sites visualized included deep dorsal vein in all 15 patients leak sites visualized included deep dorsal vein in all 15 patients (100%), cavernous veins in 7 (46,6%), glans in 4 (26,6%) and corpus spongiosum in 3 (20%). Aberrant veins documented in 4 patients (26,6%): communicating with the saphenous vein in 2 (13,3%), with scrotal veins and femoral vein in 1 (6,6%). Deep dorsal vein leakage as the only venous site was find in 2 patients (13.3%), 9 (60%) had leakage through 2 venous sites, 3 (20%) had leakage through 3 venous sites and 1 (6,6%) had leakage through 4 venous sites. Correlations among hemodynamic and radiographic observations allowed the identification of 2 types of cavernosometric findings. While type I developed an high intracavernous pressure during gravity infusion, an high intracavernous pressure was not observed in type 2. The FCG by the digital radio-fluoro-graphic digital system permit the possibility of sottraction and rielaboration of images and reduces examination and radiation time. The gravity FCM is simple, not expensive and respect the physiological intracavernous pressure.

Adult↗
PubMed1996

[Search of gravity force in the planning of arm pointing movements].

Arm movements in two directions (downward assisted by gravity and upward against gravity) with three different loads (no load 0.5 and 1 kg) were studied in six subjects. Movements of the arm were recorded using an optoelectronic (2 TV, 100 Hz) system which allowed the computer reconstruction of joint motion. Analyses focused upon finger kinematics in the sagittal plane. Subjects showed curved paths for both directions and load conditions. The path's curvature changed significantly only as a function of the direction of the movement. Velocity profiles were unimodal for all conditions. Upward movements showed greater deceleration than acceleration times in contrast to downward movements which presented more symmetrical velocity profiles. The ratio of acceleration time to total movement time changed significantly only as a function of the direction of the movement but not as a function of the load. Results from this study provide indirect evidence that the CNS executes movements by taking advantage of gravity force.

Adult↗
PubMed2000

Artificial gravity as a countermeasure in long-duration space flight.

Long-duration exposure to weightlessness results in bone demineralization, muscle atrophy, cardiovascular deconditioning, altered sensory-motor control, and central nervous system reorganizations. Exercise countermeasures and body loading methods so far employed have failed to prevent these changes. A human mission to Mars might last 2 or 3 years and without effective countermeasures could result in dangerous levels of bone and muscle loss. Artificial gravity generated by rotation of an entire space vehicle or of an inner chamber could be used to prevent structural changes. Some of the physical characteristics of rotating environments are outlined along with their implications for human performance. Artificial gravity is the centripetal force generated in a rotating vehicle and is proportional to the product of the square of angular velocity and the radius of rotation. Thus, for a particular g-level, there is a tradeoff between velocity of rotation and radius. Increased radius is vastly more expensive to achieve than velocity, so it is important to know the highest rotation rates to which humans can adapt. Early studies suggested that 3 rpm might be the upper limit because movement control and orientation were disrupted at higher velocities and motion sickness and chronic fatigue were persistent problems. Recent studies, however, are showing that, if the terminal velocity is achieved over a series of gradual steps and many body movements are made at each dwell velocity, then full adaptation of head, arm, and leg movements is possible. Rotation rates as high as 7.5-10 rpm are likely feasible. An important feature of the new studies is that they provide compelling evidence that equilibrium point theories of movement control are inadequate. The central principles of equilibrium point theories lead to the equifinality prediction, which is violated by movements made in rotating reference frames.

Coriolis Force↗
PubMed2001

Development of the gravity sensing system.

The utricle and saccule contain hair cells, which are the peripheral sensors of change in gravity that transmit signals regarding these changes to the neural components of the vestibular system. Although the fundamental neural pathways, especially the vestibular reflex pathways, have been investigated extensively, the principals underlying the functional development of this system are under study at present. The objective of this review is to identify the gravity-sensing components of the vestibular system and to present an overview of the research performed on their development. The second part of this review is focused on one important aspect of development, the emergence of electrical excitability using the chick tangential vestibular nucleus as a model. The importance of this research to understanding vestibular compensation and vestibular disturbance during spaceflight is considered. Because there is a conservation of the fundamental pathways and function in vertebrate phylogeny from birds through mammals, findings from studies on avians should contribute significantly to understanding the mechanisms operating in mammals. Also, we expect that as the events and basic mechanisms underlying normal vestibular development are revealed, these will provide practical tools to investigate the pattern of recovery from dysfunction of the vestibular system. This is related to the evidence suggesting that recovery of function in different systems and cell lines, including neurons, involves repeating certain patterns established during development.

Animals↗
PubMed1999

The role of amyloplasts during gravity perception in gynophores of the peanut plant (Arachis hypogaea).

Gravitropic perception and response are essential for the completion of the reproductive life cycle of the peanut plant (Arachis hypogaea L.). The developing seeds are buried in the soil by a specialized organ, the gynophore, allowing the fruit to mature underground. Controversy exists about the site of graviperception in the gynophore: previous workers suggested that the intercalary meristem was the zone where gravity was perceived. Taking the starch statolith hypothesis for graviperception as a framework, we explored the possibility that the starch-grain filled plastids (amyloplasts) in the starch sheath of the gynophore may be acting as gravisensors. We show that these amyloplasts sediment readily with respect to the gravity vector within 30 min of reorientation, and before there is a measurable gravitropic response. Gynophore explants were incubated with gibberellic acid and kinetin, in darkness, to remove starch from the amyloplasts. Destarching the gynophores did not inhibit overall growth of the organ, but reduced the gravitropic response curvature by 82% compared to water-treated controls. In addition, gynophores placed on a rotating clinostat (without hormone treatment) also showed a reduced gravitropic response. In conclusion, the evidence presented in this work strongly suggests that the amyloplasts of the starch sheath are responsible for gravitropic perception in the peanut gynophore. A model for graviperception in the gynophore is presented.

Arachis↗
PubMed1995

Micromanipulation of statoliths in gravity-sensing Chara rhizoids by optical tweezers.

Infrared laser traps (optical tweezers) were used to micromanipulate statoliths in gravity-sensing rhizoids of the green alga Chara vulgaris Vail. We were able to hold and move statoliths with high accuracy and to observe directly the effects of statolith position on cell growth in horizontally positioned rhizoids. The first step in gravitropism, namely the physical action of gravity on statoliths, can be simulated by optical tweezers. The direct laser microirradiation of the rhizoid apex did not cause any visible damage to the cells. Through lateral positioning of statoliths a differential growth of the opposite flank of the cell wall could be induced, corresponding to bending growth in gravitropism. The acropetal displacement of the statolith complex into the extreme apex of the rhizoid caused a temporary decrease in cell growth rate. The rhizoids regained normal growth after remigration of the statoliths to their initial position 10-30 micrometers basal to the rhizoid apex. During basipetal displacement of statoliths, cell growth continued and the statoliths remigrated towards the rhizoid tip after release from the optical trap. The resistance to statolith displacement increased towards the nucleus. The basipetal displacement of the whole complex of statoliths for a long distance (>100 micrometers) caused an increase in cell diameter and a subsequent regaining of normal growth after the statoliths reappeared in the rhizoid apex. We conclude that the statolith displacement interferes with the mechanism of tip growth, i.e. with the transport of Golgi vesicles, either directly by mechanically blocking their flow and/or, indirectly, by disturbing the actomyosin system. In the presence of the actin inhibitor cytochalasin B the optical forces required for acropetal and basipetal displacement of statoliths were significantly reduced to a similar level. The lateral displacement of statoliths was not changed by cytochalasin B. The results indicate: (i) the viscous resistance to optical displacement of statoliths depend mainly on actin, (ii) the lateral displacement of statoliths is not impeded by actin filaments, (iii) the axially directed actin-mediated forces against optical displacement of statoliths (for a distance of 10 micrometers) are stronger in the basipetal than in the acropetal direction, (iv) the forces acting on single statoliths by axially oriented actin filaments are estimated to be in the range of 11-110 pN for acropetal and of 18-180 pN for basipetal statolith displacements.

Actins↗