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PubMed1993

Quantification of trunk muscle performance in standing, semistanding and sitting postures in healthy men.

The purpose of this study was to determine trunk muscle performance in the sitting, semistanding, and standing postures during isometric and dynamic extension and flexion movements. Twenty-five male subject volunteers, with no previous history of back pain participated in the study. A triaxial dynamometer that measures torque, angular position, and velocity was used to measure isometric and dynamic motor output. The dynamometer allows testing in the sitting and standing postures. A custom-designed module also allowed testing in the semistanding posture. Each subject was tested in two sessions. The first session included the physical examination and three trials of isometric maximum voluntary contractions in the three postures. The second session included the dynamic performance against a resistance equal to 50% of the effort, as measured in the first session. Subjects were instructed to perform five repetitive flexion and extension cycles as fast and accurately as possible with maximum effort. An analysis of variance with repeated measures design was used to investigate the effects of the postures (standing, semistanding and sitting), the direction of exertion (flexion and extension), and the interaction effects of the isometric and dynamic parameters (maximum and average torque, velocity, power, and range of motion). The effects of direction (F = 98, P < 0.0001) and the interaction of posture and direction (F = 7.9, P < 0.001) were significant. The maximum isometric flexion strength was significantly higher in the standing posture than in semistanding and sitting. The maximum isometric extension was not affected by the posture (sitting, semistanding and standing).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1997

Mechanical response of the lumbar spine to seated postural loads.

STUDY DESIGN: In vitro force and deformation measurements formed the basis for determinate, quasistatic analysis of principal forces in the seated lumbar spine. OBJECTIVES: To explore the relationship between seated postures and the mechanical response in component tissues of lumbar intervertebral joints. SUMMARY OF BACKGROUND DATA: Despite the high prevalence of low back pain syndrome, the precise mechanisms relating specific mechanical loads to spinal degeneration are not well understood. Simultaneous, time-dependent measurement of anterior column forces and articular facet forces has not been presented previously. consequently, a determinate analysis of principal component forces has not been possible. METHODS: Twelve lumbar spines (L1-S1) were subjected to constant loading conditions while in flexed and extended seated postures. Time-dependent forces were measured in the anterior column at the L4 and L5 superior endplates and in the four facets of the L3-L4 and L4-L5 motion segments. A quasi-static analysis of sagittal plane forces was used to compute the remaining principal joint forces, including ligament, disc shear, and facet impingement forces. RESULTS: Component forces changed under static loading in both postures. There were significant differences between the mechanical responses of the two postures. Although the vertical creep displacement was greater in the extended seated posture (3.22 mm versus 2.11 mm), the escalation of forces was more severe in the flexed posture. CONCLUSIONS: The results suggest a mechanism of force balancing in lordotic postures under static loads, whereas flexed postures produce large increases to the tensile forces in the region of the posterior anulus.

Adult↗

PubMed1998

The correlation between surface measurement of head and neck posture and the anatomic position of the upper cervical vertebrae.

STUDY DESIGN: Repeated measurements were made of surface postural angles registering the relative positions of the head and neck in photographs and of angles of the upper cervical vertebrae recorded in lateral cephalometric radiographs in the same subjects. For all registrations, subjects assumed the natural head rest position. OBJECTIVES: To examine the correlation between external measurement of head and neck posture and the anatomic positions of the upper four cervical vertebrae. SUMMARY OF BACKGROUND DATA: Interpretation of surface cervical posture measurement is confounded by lack of knowledge about the extent of the underlying compensatory adjustments among the upper cervical vertebrae that may accompany variation in head and neck posture. The correlation between surface measurement and postural characteristics of the upper cervical spine has not been reported to date. METHODS: The association between a set of angles describing the anatomic position of the four upper cervical vertebrae on lateral cephalometric radiographs and a surface measurement of head and neck posture, the craniovertebral angle, was studied in 34 young adult women aged between 17.2 and 30.5 years, mean age, 24.5 years. Anatomic positions of the upper four cervical vertebrae were expressed by angles relative to the true vertical or horizontal. Surface angles registering head and neck position for each subject were obtained from photographs recorded on two occasions. RESULTS: No strong correlation could be established between the angles taken from the lateral cephalometric radiographs measuring the extent of upper cervical lordosis, orientation of the atlas, vertebral inclination, or odontoid process tilt and surface angles recording head and neck position. This finding was attributed principally to the much greater positional variability demonstrated within the upper cervical spine when compared with the surface measurements of head and neck position. CONCLUSION: Anatomic alignment of the upper cervical vertebrae cannot be inferred from variation in surface measurement of head and neck posture. This is the case even in those people identified with more extreme head and neck postural tendencies.

Adolescent↗

PubMed2001

A comparison between bipedal and quadrupedal rats: do bipedal rats actually assume an upright posture?

STUDY DESIGN: A basic science animal investigation. OBJECTIVES: To determine if bipedal rats differ in upright posture compared with quadrupedal rats. SUMMARY OF BACKGROUND DATA: It has been reported that surgically induced bipedalism in the rat leads to habitual upright posture. Based on this finding, bipedal rats have been used to study the changes erect posture induces in bone, ligament, muscle, and intervertebral discs. Previous studies have used direct observation as a means to describe posture. This study is the first to quantify postural differences between bipedal and quadrupedal rats. METHODS: Eleven bipedal rats were created by forelimb and tail amputation within 24 hours of birth. Eleven quadrupedal rats served as controls. Specialized cages were used with infrared sensors, and a computer program measured the total amount of time in the upright stance, the number of stands, and the amount of horizontal movement in the upright stance. Statistical comparisons were made between bipedal and quadrupedal rats hourly and over a 24-hour period of time. RESULTS: Quadrupedal rats assumed an upright posture for a significantly greater amount of time than bipedal rats when monitored over 24 hours (P = 0.016). Quadrupedal and bipedal rats did not differ in the number of stands (P = 0.63) or in the amount of horizontal movement in the upright stance (P = 0.34) over 24 hours. Similar results were obtained when comparing hourly intervals. CONCLUSION: This study quantifiably indicates that bipedal rats do not assume a more erect posture and spend no more time in an upright position compared with quadrupedal rats. The upright posture may not be the cause of some previously reported anatomic changes observed in the bipedal rat.

Amputation, Surgical↗

PubMed2002

The effect of different standing and sitting postures on trunk muscle activity in a pain-free population.

STUDY DESIGN: A normative, single-group study was conducted. OBJECTIVE: To determine whether there is a difference in electromyographic activation of specific lumbopelvic muscles with the adoption of common postures in a pain-free population. SUMMARY OF BACKGROUND DATA: Clinical observations indicate that adopting passive postures such as sway standing and slump sitting can exacerbate pain in individuals with low back pain. These individuals often present with poor activation of the lumbopelvic stabilizing musculature. At this writing, little empirical evidence exists to document that function of the trunk and lumbopelvic musculature are related to the adoption of standardized standing and sitting postures. METHODS: This study included 20 healthy adults, with equal representation of the genders. Surface electromyography was used to measure activity in the superficial lumbar multifidus, internal oblique, rectus abdominis, external oblique, and thoracic erector spinae muscles for four standardized standing and sitting postures. RESULTS: The internal oblique, superficial lumbar multifidus, and thoracic erector spinae muscles showed a significant decrease in activity during sway standing (P = 0.027, P = 0.002, and P = 0.003, respectively) and slump sitting (P = 0.007, P = 0.012, and P = 0.003, respectively), as compared with erect postures. Rectus abdominis activity increased significantly in sway standing, as compared with erect standing (P = 0.005). CONCLUSIONS: The findings show that the lumbopelvic stabilizing musculature is active in maintaining optimally aligned, erect postures, and that these muscles are less active during the adoption of passive postures. The results of this study lend credence to the practice of postural retraining when facilitation of the lumbopelvic stabilizing musculature is indicated in the management of specific spinal pain conditions.

Abdomen↗

PubMed2004

Effect of training on postural control in figure skaters: a randomized controlled trial of neuromuscular versus basic off-ice training programs.

OBJECTIVES: To compare the effect of a neuromuscular training program and a basic exercise program on postural control in figure skaters. DESIGN: Two groups; parallel design; prospective, randomized controlled trial. SETTING: Postural control laboratory, arenas, September 2001 to December 2002. PARTICIPANTS: Forty-four young, healthy figure skaters (18 years +/- 3 years). INTERVENTIONS: Participants were randomly assigned to receive a neuromuscular training program (n = 22) or a basic exercise training program (n = 22). Both programs were completed 3 times per week for 4 weeks, and each session was supervised. MAIN OUTCOME MEASUREMENTS: Participants completed baseline and postintervention measures of postural control on a force plate. Postural control was quantified as the center of pressure (CoP) path length during tests of single-limb standing balance that mimicked figure skating skills and challenged the postural control system to varying degrees. The primary outcome measure was the CoP path length observed during a landing jump test completed with eyes closed. RESULTS: The post intervention CoP path lengths during the more challenging tests were significantly (P < 0.05) lower (indicating better postural control) for the neuromuscular trained group than for the basic exercise-trained group. For the landing jump test completed with eyes closed, the percent improvement in the neuromuscular trained group was significantly greater (mean = 21.0 +/- 22.0%) than the basic exercise trained group (mean = -4.9 +/- 24.9%; P < 0.05). The magnitude of improvement in the neuromuscular-trained group ranged from approximately 1% to 21%, depending on the specific postural control test used. CONCLUSIONS: The results suggest that off-ice neuromuscular training can significantly improve postural control in figure skaters, whereas basic exercise training does not.

Adolescent↗

PubMed1989

Posture of low-risk preterm infants between 32 and 36 weeks postmenstrual age.

The supine posture of 15 low-risk preterm infants was studied to establish whether they have a preferred posture and, if so, whether it changes with age. No over-all preferred posture was found. Almost always one posture was adopted most frequently, but often a great variety of other postures were adopted almost as frequently. There was no correlation between postmenstrual age and preferred posture, the number of different postures, or the duration of longest uninterrupted posture.

Child Development↗

PubMed1994

Postural stability of workers exposed to lead.

OBJECTIVE: To detect, with a computerised postural sway measurement system, any significant deviation of postural sway parameters among lead workers compared with a control group. METHODS: Postural stability was investigated with a computerised postural sway measurement system in 60 workers exposed to lead with a duration of exposure of 84 (range 3-366) months and 60 controls. Sway parameter data were collected with an Advanced Mechanical Technology computerised biomechanics platform system. RESULTS: The mean current blood lead concentration was 36.0 (range 6.4 to 64.5) micrograms/dl for the exposed workers and 6.3 (range 3.1 to 10.9) micrograms/dl for the 14 controls. There was no significant difference between the groups for the postural sway parameters obtained when the eyes were open. Significant differences were found for Xs, Ys (SDs of the coordinates of the centre of pressure); Xm, Ym (mean deviation of the coordinates of the centre of pressure); Rm (average displacement of Xi, Yi, from Xo, Yo); L (length of sway path); Vel (mean velocity of the centre of pressure along its path); Ao (area included within the path of the centre of pressure); Ae (95% confidence elliptical area). The Romberg ratios (the relation between eyes closed and open) for the Vel, L, Ao and Ae of the exposed workers were also significantly different from the controls. CONCLUSION: The study showed that workers exposed to lead had significantly poorer postural stability than the controls. Lead may affect certain parts of the whole sensory neural axis resulting in postural instability when the visual input is cut off. Based on current blood lead concentrations, we were not able to obtain any significant association with the postural sway parameters.

Adult↗

PubMed1998

Effects of meal volume and posture on gastric emptying of solids and appetite.

The effects of volume and posture on gastric emptying and intragastric distribution of a solid meal and appetite were evaluated. Eight normal volunteers were studied on four occasions, on each of which a meal comprising ground beef mixed with tomato sauce of either 650 g ("large") or 217 g ("small") was eaten. Two studies were performed while the subject was lying in the left lateral decubitus position, and two studies were performed while the subject was sitting so that in each subject data were available for both meals and in both postures. Hunger and fullness were evaluated using a visual analog questionnaire. In both postures and after both meals, gastric emptying approximated a linear pattern after an initial lag phase. The lag phase was shorter for the large meal when compared with the small meal [sitting: large 13 +/- 5 vs. small 29 +/- 7 min; left lateral: large 16 +/- 3 vs. small 24 +/- 3 min, F(1, 7) = 46.3, P < 0.0005]. In both postures the contents of the total [F(1,7) = 1794.5, P < 0.0001], proximal [F(1,7) = 203.7, P < 0.0001], and distal [F(1,7) = 231.5, P < 0.0001] stomach were greater after the large meal when compared with the small meal. Although the 50% emptying time was greater with the large than the small meal [F(1,7) = 40.8, P < 0.001], the postlag emptying rate (g/min) was more rapid with the large meal [sitting: large 1.7 +/- 0.2 vs. small 1.1 +/- 0. 1 g/min; left lateral: large 1.8 +/- 0.1 vs. small 1.3 +/- 0.04 g/min, F(1,7) = 44.7, P < 0.0005]. There was a significant interaction between meal volume and posture for retention in the distal stomach [F(1,7) = 7.14, P < 0.05]. Contrasts were used to evaluate the effects of volume and posture between the four studies and demonstrated an effect of posture for the large [F(1,21) = 18.7, P < 0.005] but not the small [F(1,21) = 0.30, P = 0.60] meal so that the retention was greater in the sitting when compared with the left lateral position. The magnitude of the postprandial increase in fullness [F(1,7) = 7.8, P < 0.05] and reduction in hunger [F(1,7) = 5.9, P < 0.05] was greater with the large meal. We conclude that meal volume has a major effect on gastric emptying; in contrast posture has only a minor impact on intragastric meal distribution, which is observed only after a large meal, and no effect on gastric emptying.

Adolescent↗

PubMed1985

Human esophageal pressures and chest wall configuration in upright and head-down posture.

Pressures were measured at two levels in the esophagus in 14 young healthy subjects performing slow inspiratory and expiratory vital capacity (VC) maneuvers in upright and head-down posture (180 degrees body tilt). In both postures, a gravitational pressure gradient was found, which increased very slightly with decreasing lung volumes (0.006 cmH2O X % VC-1 X cm descent-1) except for upright expiratory curves above 60% VC. The expiratory pressure gradient tended to be larger in head-down than in upright posture; however, during inspiration the opposite was true. In both postures the pressure change between 100 and 20% VC was smaller in the uppermost zone, which is consistent with the smaller changes in alveolar expansion in this zone. Also, in seven of the subjects, changes in cross-sectional area of the middle and lower part of the rib cage (HRC and LRC) and of the abdomen (ABD) were measured by respiratory inductive plethysmography in upright and head-down posture. The ratio of HRC motion to LRC motion was constant throughout the VC and did not change with posture, yet the ratio of ABD motion to mean RC motion changed with overall volume and was also larger in head-down than in upright posture. In conclusion, the changes in esophageal pressure gradient during slow VC maneuvers in head-down vs. upright posture were not related to (and thus not caused by) changes in chest wall configuration.

Adult↗

PubMed1992

Development of anticipatory postural adjustments during locomotion in children.

1. Anticipatory postural adjustments were studied in children (6-14 yr of age) walking on a treadmill while pulling a handle. Electromyographs (EMGs) and movements were recorded from the left arm and leg. 2. Postural activity in the leg muscles preceded voluntary arm muscle activity in all age groups, including the youngest children (6 yr of age). The latency to both leg and arm muscle activity, from a triggering audio signal, decreased with age. 3. In older children the latency to both voluntary and postural activity was influenced by the phase of the step cycle. The shortest latency to the first activated postural muscle occurred during single support phase in combination with a long latency to arm muscle activity. 4. In the youngest children, there was no phase-dependent modulation of the latency to the activation of the postural muscles. The voluntary activity was delayed during the beginning of the support phase resulting in a long delay between leg and arm muscle activity. 5. The postural muscle activation pattern was modified in a phase-dependent manner in all children. Lateral gastrocnemius (LG) and hamstring muscles (HAM) were activated during the early support phase, whereas tibialis anterior (TA) and quadriceps (Q) muscles were activated during the late support phase and during the swing phase. However, in the 6-yr-old children, LG was also activated in the swing phase. LG was activated before the HAM activity in the youngest children but after HAM in 14-yr-old children and adults. 6. The occurrence of LG activity in postural responses before heel strike suggests an immature (nonplantigrade) gating of postural activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1995

Bilateral labyrinthectomy in the cat: effects on the postural response to translation.

1. This study examined the role of vestibular afferent information on the postural responses of four cats, evoked by movements of the support surface during stance. Animals were exposed to linear translations of the supporting surface in eight evenly spaced directions in the horizontal plane, before and after bilateral labyrinthectomy. Postural responses were quantified in terms of the ground reaction forces under each paw and the evoked activity in selected muscles. 2. The cats were able to stand on the platform within 1-3 days after labyrinthectomy and were able to maintain balance during all perturbations of stance, even when they stood in total darkness, completely deprived of visual information. After lesion, postural responses were characterized by normal latency and normal spatial and temporal patterning of electromyographic (EMG) response. The pattern of force response showed the force constraint strategy that characterizes postural responses in the intact animal. 3. The only deficit in the postural response after lesion was a hypermetria, or active over-response that caused the animals to overbalance somewhat but did not impair their ability to remain upright. Analysis of the trajectory of the animal's center of mass during the trials indicated that the hypermetria was due to an abnormally large, active response on the part of the animal and could not be attributed to changes in the passive stiffness of the musculoskeletal system. The hypermetria was transient, and response amplitude returned to control levels after the rapid compensation phase of 10-15 days. 4. It is concluded that vestibular information is not essential for triggering the rapid, automatic postural response to translations of the support surface, nor is it necessary for the selection or shaping of the evoked response. Instead, somatosensory information appears to predominate in these postural adjustments. However, vestibular afferent input does influence the scaling of the postural response.

Afferent Pathways↗

PubMed1996

Forms of forward quadrupedal locomotion. I. A comparison of posture, hindlimb kinematics, and motor patterns for normal and crouched walking.

1. Posture, hindlimb kinematics, and activity patterns of selected hindlimb muscles were compared for normal and crouched treadmill walking (0.5-0.6 m/s) for eight cats. To elicit crouched walking in which the trunk and head were lowered, cats were encouraged to walk under a light-weight Plexiglas ceiling suspended 17-20 cm above the treadmill belt. Kinematic data were obtained from high-speed ciné film, and electromyograms (EMGs)-synchronized with the kinematic records-were taken from 11 hindlimb muscles. 2. The postures for the two forms of walking were distinctly different. During crouched walking, each cat lowered its entire body keeping its trunk horizontal to the treadmill belt. Also the head was lowered, with the top of the head in line with the dorsal surface of the trunk. Hip height, used as a measure for hindlimb crouch, was reduced by 30%, from an average height of 23 cm to an average height of 16 cm above the belt during the entire step cycle. 3. Average cycle periods (766 +/- 30 ms, mean +/- SD) and percentage of time devoted to swing (30%) and stance (70%) were similar for normal and crouched walking. The profiles of the hindlimb kinematics were also similar for the hip, knee, ankle, and metatarsophalangeal (MTP) joints during the step cycle, but the timing of some of the motion reversal, as well as the ranges of motion during various phases, were different at some joints for the two forms of walking. 4. During the swing phase, the transition between the flexion and extension (F-E1 reversal) occurred later in the normalized swing phase at the hip, knee, and ankle joints, and the range of flexion was increased at each joint. With greater flexion at these joints, the anatomic axis of the hindlimb (measured from hip joint to toe) was decreased and the hind paw advanced in the narrow space between the abdomen and treadmill belt. At contact, the position of the paw was less anterior to the perpendicular reference line (hip joint marker to belt) and all joints were more flexed for crouched than normal walking. 5. Throughout the stance phase, the knee and ankle joints remained significantly more flexed by 41-45 deg during crouched than normal walking. Although the hip and MTP joints started in a more flexed position at paw contact, both joints extended more during stance for crouched than normal walking, and at the time of peak extension (just before paw lift-off), the degree of extension at the hip and MTP joints was similar for both forms of walking. 6. Muscle patterns for crouched and normal walking were similar with some exceptions. The burst durations for three primary flexor muscles, the semitendinosus (knee flexor), extensor digitorum longus (EDL, ankle flexor), and flexor digitorum longus (digit flexor) were longer for crouched than normal walking, and this was consistent with the increased range and duration of flexion during the swing phase of crouched walking. Also, two muscles that normally showed mainly swing-related activity during normal walking, the EDL and the extensor digitorum brevis, had distinct stance-related bursts that occurred after midstance during crouched walking. 7. Crouched walking requires a postural change that typically occurs when cats stalk prey and when cats walk up and down sleep slopes. Postural set during walking appears to be determined by brain stem and diencephalic centers, and the postural orientation of the cat may require adjustments in the motor program provided by spinal centers for the cat to walk. The role of posture and locomotion and the adjustments in hindlimb kinematics and EMG activity patterns have been studied for forward and backward walking in the cat and now for crouched walking on the treadmill. These data will assist us in understanding the role of posture, especially crouched posture, during other walking behaviors.

Animals↗

PubMed1992

Effect of body posture on concentration-response curves to inhaled methacholine.

Lung volume has been shown to be a major determinant of the bronchoconstrictor response to inhaled methacholine (MCh). Because a change in body posture from sitting to supine is associated with a reduction in lung volume, we hypothesized that airway responsiveness to inhaled MCh should be affected by body posture. Responsiveness to MCh was assessed in both sitting and supine postures on separate days in 10 subjects aged 24 to 42 yr. Subjects inhaled aerosols of saline and MCh in progressively doubling concentration (0.125 to 256 mg/ml). Responses were assessed by measuring partial and complete forced expiratory flow-volume curves (PEFV and MEFV, respectively). As indices of airway responsiveness, we took the MCh concentration ([MCh]) at which the FEV1 fell by 10% relative to postsaline (PC10), the maximal percentage fall in FEV1 (MR), the [MCh] at which FEV1 reached 50% of MR (EC50), and the [MCh] at which the flow at 20% vital capacity on PEFV curves fell by 20% relative to postsaline (FP20). Responsiveness to MCh was increased in the supine compared with the sitting posture. In the sitting posture, the geometric mean values of MR, PC10, and FP20 were 16.3%, 16.3 mg/ml, and 2.0 mg/ml; supine they were 29.9% (p less than 0.009), 3.0 mg/ml (p less than 0.02), and 0.6 mg/ml (NS), respectively. EC50 did not change with posture. These results are consistent with the notion that airway responsiveness is influenced by airway-parenchymal interdependence and indicate that the results of bronchial provocation testing in the supine posture cannot be directly compared with those in the upright posture.

Adult↗

PubMed1987

Effect of upright posture on the aldosterone responses to dopamine, metoclopramide, angiotensin II, and adrenocorticotropin.

Aldosterone secretion in man is stimulated by potassium (K), ACTH, and angiotensin II (AII) and inhibited by dopamine (DA). In normal sodium-replete supine individuals, aldosterone secretion is under maximum tonic inhibition by DA and is not inhibited further by DA administration. Sodium depletion alters plasma aldosterone responses to secretogogues. Upright posture, another physiological stimulus to aldosterone secretion, recently was demonstrated to sensitize the adrenal cortex to inhibition of aldosterone secretion by a large quantity of DA (4.0 micrograms/kg X min). The effect of upright posture on aldosterone responses to other secretogogues is unknown. In this study, we investigated the effect of upright posture on aldosterone responses to low infusion rates of DA, to the DA antagonist metoclopramide (M) and to AII and ACTH. Fourteen normal men eating a normal sodium diet were studied. In eight, PRA, plasma aldosterone (PAC), plasma cortisol (F), and serum K concentrations were determined after 4 h of upright posture and infusion of vehicle (D5W) or DA at 0.1, 0.4, and 2.0 micrograms/kg X min. Six other normal men were kept supine for 3 h and, on separate days, upright for 3 h and given iv M (10-mg bolus dose), AII (1 and 4 pmol/kg X min for 30 min), and ACTH (20 and 120 mU/h for 30 min). PAC, PRA, F, and K were measured before and after these three secretogogues were administered. In the presence of vehicle, mean PAC increased by 15.1 +/- 4.3 (+/- SEM) ng/dL after 4 h of upright posture. In the presence of DA infused at 0.1, 0.4, and 2.0 micrograms/kg X min, the PAC response to upright posture was decreased to 9.7 +/- 2.5 (P = NS), 7.5 +/- 3.9 (P less than 0.05), and 8.1 +/- 2.0 (P less than 0.05) ng/dL, respectively. This occurred without a decrease in PRA, F, or K. The stimulation of PAC 10 and 20 min after a 10-mg bolus dose of M was 9.6 +/- 3.3 and 9.3 +/- 2.6 ng/dL, respectively, in supine subjects and 8.3 +/- 2.3 and 10.8 +/- 3.4 ng/dL 10 and 20 min after the M dose in upright subjects. The responses of PAC to ACTH and AII also were unchanged after 3 h of upright posture. We conclude that upright posture sensitizes the adrenal cortex to inhibition of aldosterone secretion by DA without affecting other modifiers of aldosterone secretion.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenocorticotropic Hormone↗

PubMed1998

Effect of body posture on spirometric values and upper airway obstruction indices derived from the flow-volume loop in young nonobese subjects.

STUDY OBJECTIVE: To define the effect of changes in body posture on flow-volume loops (FVLs) and four commonly used indices of upper airway obstruction (UAO) in young, nonobese normal subjects. DESIGN: Prospective comparative study. SETTING: Pulmonary function laboratory at an academic hospital. PARTICIPANTS: Thirty-one normal volunteers. INTERVENTION: At least three FVLs per posture were obtained in the sitting, supine, and left and right lateral recumbent postures while maintaining a constant position of the head and neck in relation to the trunk. In each body posture, the largest observed flow rates were used to calculate the UAO indices. RESULTS: When subjects changed from the sitting to each of the three recumbent postures, all spirometric values decreased significantly (p<0.0001). However, among the four UAO indices, only the FEV1/peak expiratory flow ratio increased significantly (although only slightly, by 2.9 and 4.4%, respectively) in both the right and left lateral recumbent postures (p<0.0001), but not in the supine posture. None of the subjects developed an inspiratory or expiratory plateau on the FVL in any of the three recumbent postures. CONCLUSIONS: In young, nonobese normal subjects, recumbency does not induce UAO, at least not detectable by changes in the FVL configuration or in UAO indices derived from the FVL. Furthermore, the study provides the upper limits of recumbency-related changes in the various UAO indices for young, nonobese normal subjects.

Adult↗

PubMed1984

The effects of postural changes on ADH release and the renal handling of sodium and water in patient with idiopathic edema.

In order to investigate the role of ADH and the renal handling of sodium and water in patients with idiopathic edema, 21 patients were subjected to acute oral water load tests. Although a normal water diuresis was observed in al patients in supine posture, it was markedly impaired in upright posture with significant decreases in sodium, free water, and osmolar clearances. In particular, two patients exhibited the continuous production of concentrated urine after the water load in upright posture. The fractional reabsorption of sodium at the proximal tubules was significantly increased in upright posture, while the glomerular filtration rate did not change significantly. The constricting of both legs with elastic bandages tended to improve the water diuresis in upright posture, suggesting that the pooling of blood into the lower legs might be contributing to the formation of idiopathic edema. The patients showed normal osmoregulation of ADH release in supine, but not in upright posture: the suppression of ADH release in upright posture was only transient or incomplete despite a sufficient fall in plasma osmolality following the water load. Thus, both an increase in renal sodium reabsorption and the insufficient suppression of ADH release in upright posture might contribute to the retention of body fluid in patients with idiopathic edema.

Adolescent↗

PubMed2002

A statistical method for predicting automobile driving posture.

A new model for predicting automobile driving posture is presented. The model, based on data from a study of 68 men and women in 18 vehicle package and seat conditions, is designed for use in posturing the human figure models that are increasingly used for vehicle interior design. The model uses a series of independent regression models, coupled with data-guided inverse kinematics, to fit a whole-body linkage. An important characteristic of the new model is that it places greatest importance on prediction accuracy for the body locations that are most important for vehicle interior design: eye location and hip location. The model predictions were compared with the driving postures of 120 men and women in five vehicles. Errors in mean eye location predictions in the vehicles were typically less than 10 mm. Prediction errors were largely independent of anthropometric variables and vehicle layout. Although the average posture of a group of people can be predicted accurately, individuals' postures cannot be predicted precisely because of interindividual posture variance that is unrelated to key anthropometric variables. The posture prediction models developed in this research can be applied to posturing computer-rendered human models to improve the accuracy of ergonomic assessments of vehicle interiors.

Adult↗