Head posture in the Hominoidea

The angle between the antero-posterior plane of the occipital condyles and a vertical axis at right angles to the Frankfort Horizontal was measured in Homo sapiens, Gorilla, Pan, Pongo and casts of two Neanderthal skulls, the Rhodesian skull and three australopithecine skulls. The angle was much greater in adult Homo sapiens and in the Neanderthal and australopithecine casts than in the adult groups of the three apes. In the immature groups, the angle underwent little change with age in Homo sapiens but in Gorilla and Pan the angle decreased markedly during the growth period. These findings can be readily correlated with the habitual bodily posture of each of the extant genera. In Homo sapiens , an upright posture is adopted early in life while in the African apes the young tend to move by brachiation and thus have an habitual posture of the spine closer to the vertical than in the "knuckle walking" adults. The large value of the angle in the Neanderthal casts also correlates well with the now widely held view that this group has a fully upright posture. However, the finding of a relatively low value for the angle in adult Pongo —a brachiator—runs counter to the general thesis that the angle is a direct reflection of overall posture and casts some doubt upon a conclusion that the large value of the angle in the australopithecine fossils necessarily indicates that these creatures stood upright.     

重力对锥形血管中血流压力的影响——基于考虑体位改变的三维流固耦合数学模型

重力是体位改变过程中最基本的生物力学刺激因素．血流压力是表征心血管功能状态的一个基本指标．目前,体位改变影响心血管系统的确切内部机制尚不清楚．为此,采用在流体和固体方程中分别引入体力项的方法,建立一个基于血流动力学概念的三维流固耦合数学模型,用以研究体位改变,确切量化重力对血流压力的影响．通过数值计算,得到以下结果．水平卧位条件下：a．单一血管中血流压力由无重力影响的轴对称二维分布变为重力影响下的三维不对称分布;b．随着进出口压差由小变大,重力对压力分布和极值的影响由大变小,当压差值分别达到10 665.6 Pa(80 mmHg)和2 666.4 Pa(20 mmHg)时,重力的影响就不再随进出口压差增大而变化;对三维单一流体,重力影响的总体趋势类似．对正、倒直立位,压力均为二维轴对称分布,其重力影响强度约为水平卧位的2倍以上．结果表明：基于血流动力学概念,引入体力项,建立三维流固耦合模型为研究体位改变提供了一种新思路,重力对单一血管中血流压力分布和大小的影响因体位不同而不同,并与进出口压差密切相关,提示,若血管进出口压差较小,忽略重力影响,不考虑体位改变,以二维轴对称模型来研究血管中血流状态,须谨慎解释所得结果．     

Dynamic stability of a human standing on a balance board

The neuromuscular system used to stabilize upright posture in humans is a nonlinear dynamical system with time delays. The analysis of this system is important for improving balance and for early diagnosis of neuromuscular disease. In this work, we study the dynamic coupling between the neuromuscular system and a balance board—an unstable platform often used to improve balance in young athletes, and older or neurologically impaired patients. Using a simple inverted pendulum model of human posture on a balance board, we describe a surprisingly broad range of divergent and oscillatory CoP/CoM responses associated with instabilities of the upright equilibrium. The analysis predicts that a variety of sudden changes in the stability of upright postural equilibrium occurs with slow continuous deterioration in balance board stiffness, neuromuscular gain, and time delay associated with the changes in proprioceptive/vestibular/visual-neuromuscular feedback. The analysis also provides deeper insight into changes in the control of posture that enable stable upright posture on otherwise unstable platforms.     

The morphology of the gluteus maximus during human evolution: Prerequisite or consequence of the upright bipedal posture?

The human gluteus maximus differs from that of the other hominoids because of its size and bony attachments. These differences raise questions concerning their sequence of appearance in human evolution. Given that humans practice a unique locomotor style, one wonders if the human gluteus maximus morphology is a prerequisite or a consequence of upright bipedal locomotion. This question is addressed using a computer model that evaluates muscle leverage in a variety of locomotor postures. In this model, the human-like, or ape-like, muscular pattern is imposed upon a representative hindlimb of each of the five extant hominoids. Shapes of the skeletal elements (i.e. ilium and ischium lengths) are adjusted in the computer to simulate an evolutionary progression from an ape to a human skeletal morphology. Changes in the leverage of different parts of the gluteus maximus (measured as moment arms) are monitored during this transition. The results show how the mechanical leverages of the gluteus maximus would have changed in a variety of hypothetical evolutionary sequences that describe an ape to human transition. Although the hominoid models exhibit minor differences in these simulations, they all show that the postural and locomotor functions of the gluteus maximus would become more difficult if musculoskeletal morphology changed to the human-like pattern before erect bipedal posture was adopted. Conversely, small adjustments in the ape-like musculoskeletal condition support an erect bipedal posture. These results suggest that a human like posture would have preceded the appearance of the human-like musculoskeletal morphology. Human gluteal morphology, therefore, is a consequence and not a prerequisite of the upright bipedal posture.     

Torsion and Bending in the Neck and Tail of Sauropod Dinosaurs and the Function of Cervical Ribs: Insights from Functional Morphology and Biomechanics

The long necks of sauropods have been subject to many studies regarding their posture and flexibility. Length of the neck varies among groups. Here, we investigate neck posture and morphology in several clades from a mechanical viewpoint. Emphasis is put on comparing sauropod necks and tails with structures in living archosaurs and mammals. Differences in the use made of necks and tails lead to clear-cut differences in the mechanical loads occurring in the same models. Ways of sustaining loads are identified by theoretical considerations. If the observed skeletal structures are suited to resist the estimated loading in a particular posture, this concordance is taken as an argument that this posture or movement was of importance during the life of the individual. Apart from the often-discussed bending in side view, we analyze the often overlooked torsion. Because torsional stresses in a homogenous element concentrate near the periphery, a cylindrical cross section gives greatest strength, and the direction of forces is oblique. In a vertebrate neck, during e.g. shaking the head and twisting the neck, oblique muscles, like the mm. scaleni, if activated unilaterally initiate movement, counterbalance the torsional moments and keep the joints between neck vertebrae in equilibrium. If activated bilaterally, these muscles keep the neck balanced in an energy-saving upright posture. The tendons of the mm. scaleni may have ossified as cervical ribs The long cervical ribs in brachiosaurids and mamenchisaurids seem to have limited flexibility, whereas the shorter cervical ribs in Diplodocidae allowed free movement. The tails of sauropods do not show pronounced adaptation to torsion, and seem to have been carried more or less in a horizontal, extended posture. In this respect, sauropod tails resemble the necks of herbivorous cursorial mammals. These analyses provide an improved understanding of neck use that will be extended to other sauropods in subsequent studies.     

Experimental alteration of limb posture in the chicken (Gallus gallus) and its bearing on the use of birds as analogs for dinosaur locomotion

Extant birds represent the only diverse living bipeds, and can be informative for investigations into the life‐history parameters of their extinct dinosaurian relatives. However, morphological changes that occurred during early avian evolution, including the unique adoption of a nearly horizontal femoral orientation associated with a shift in center of mass (CM), suggest that caution is warranted in the use of birds as analogs for nonavian dinosaur locomotion. In this study, we fitted a group of white leghorn chickens (Gallus gallus) with a weight suspended posterior to the hip in order to examine the effects on loading and morphology. This caused a CM shift that necessitated a change in femoral posture (by 35° towards the horizontal, P < 0.001), and resulted in reorientation of the ground reaction force (GRF) vector relative to the femur (from 41° to 82°, P < 0.001). Despite similar strain magnitudes, an overall increase in torsion relative to bending (from 1.70 to 1.95 times bending, P < 0.001) was observed, which was weakly associated with a tendency for increased femoral cross‐sectional dimensions (P = 0.1). We suggest that a relative increase in torsion is consistent with a change in femoral posture towards the horizontal, since this change increases the degree to which the bone axis and the GRF vector produce mediolateral long‐axis rotation of the bone. These results support the hypothesis that a postural change during early avian evolution could underlie the allometric differences seen between bird and nonavian dinosaur femora by requiring more robust femoral dimensions in birds due to an increase in torsion. J. Morphol. 240:237–249, 1999. © 1999 Wiley‐Liss, Inc.     

The first rib of hominoids

Homo sapiens is unique among extant hominoids in displaying a univertebral articular pattern for the first rib; that is, the head of the first rib articulates only with the body of the first thoracic vertebra. All other hominoids, indeed virtually all other mammals, display a bivertebral pattern; that is, the head of the first rib articulates with the bodies of both the seventh cervical and the first thoracic vertebrae, as well as the intervening disk. Two fossil hominid partial first ribs, A.L. 288-lax and A.L. 333-118, show that the univertebral pattern was fully established in the hominid lineage by the appearance of Australopithecus afarensis. Four hypotheses, based in functional anatomy, can be postulated for the evolution of the univertebral pattern: (1), it increases the volume (via increased length) of the neck, which could, in turn, compensate for the functional loss of the laryngeal sac systems in hominid vocalization; (2), it is a consequence of the more barrel-shaped thorax in hominids; (3), it is a consequence of functional modifications in the hominid shoulder girdle; and/or (4), it is a consequence of modifications in hominid first rib motion while breathing in an upright stance. Fossil evidence supports all but the first hypothesis, and most strongly supports the third. However, evidence for the first hypothesis does suggest that the evolution of descent of the upper respiratory system in the hominid lineage may have been permitted by the presence of the univertebral pattern, while the reverse is probably not true. Furthermore, fossil evidence for the third hypothesis shows that, by the appearance of A. afarensis, the hominid upper limb had been freed from locomotor constraints, which concomitantly confirms full adaptation to upright posture. Thus, because of their potential relationship with upright posture, the two remaining hypotheses (i.e., "thoracic shape" and "first rib movement during breathing") also have support from the fossil evidence.     

Mechanisms of reference posture correction in the system of upright posture control

It was earlier shown that ultraslow tilts of the support under quiet standing conditions evoke an unusual response reflecting the operation of compensatory mechanisms: postural sway is a superposition of postural oscillations typical of quiet standing and greater, slower inclinations of the body caused by the tilt. This may be explained by the presence of two hierarchical levels of upright posture control: real-time control compensates for small deviations of the body from the reference posture prescribed by presetting control. Mathematical simulation methods have been used to study the mechanisms of reference posture control. The results are compared with available experimental data. It is demonstrated that the reference posture can be corrected according to the gravitational vertical with the use of a kinesthetic reference alone. It is hypothesized that, when correcting the reference posture, the nervous system “assumes” the support to be immobile. The afferent input from sole pressure receptors is an important factor in reference posture correction. The advantages of the putative two-level control over control based on an explicit internal model are discussed.     

The role of the mechanical system in control: a hypothesis of self-stabilization in hexapedal runners

To explore the role of the mechanical system in control, we designed a two dimensional, feed-forward, dynamic model of a hexapedal runner (death-head cockroach, Blaberus discoidalis). We chose to model many-legged, sprawled posture animals because of their remarkable stability. Since sprawled posture animals operate more in the horizontal plane than animals with upright postures, we decoupled the vertical and horizontal plane and only modelled the horizontal plane. The model was feed-forward with no equivalent of neural feedback among any of the components. The model was stable and its forward, lateral and rotational velocities were similar to that measured in the animal at its preferred velocity. It also self-stabilized to velocity perturbations. The rate of recovery depended on the type of perturbation. Recovery from rotational velocity perturbations occurred within one step, whereas recovery from lateral perturbations took multiple strides. Recovery from fore-aft velocity perturbations was the slowest. Perturbations were dynamically coupled--alterations in one velocity component necessarily perturbed the others. Perturbations altered the translation and/or rotation of the body which consequently provided ''mechanical feedback'' by altering leg moment arms. Self-stabilization by the mechanical system can assist in making the neural contribution of control     

The oldest ape

This paper recounts the history and significance of Morotopithecus bishopi, an early Miocene East African ape. Morotopithecus differs in intriguing ways from its contemporary Proconsul. While craniodental differences are slight, the known elements of its postcranium suggest that Morotopithecus was capable of modern ape–like positional behaviors, including vertical postures, deliberate climbing, and arm hanging. In contrast, Proconsul and other early and middle Miocene hominoids have been reconstructed as above–branch quadrupeds. Paleoanthropologists are currently divided over whether and which of the anatomical features associated with upright posture and suspension in the modern apes are due to inheritance or independent evolution. This debate has important implications for interpreting the phylogenetic positions of both Morotopithecus and Proconsul, as well as for reconstructing the pattern and timing of the emergence of modern ape adaptations.     

Interaction between Visual and Proprioceptive Analyzers in Vertical Posture Control

The CNS can precisely assess the spatial position of the human body only by simultaneously processing and integrating the visual, proprioceptive, and vestibular inputs. Postural stability data make it possible to estimate changes taking place in the function of analyzers involved in the maintenance of the upright posture. The vertical posture stability was assessed in healthy children and children with spastic diplegic cerebral palsy from their postural responses to the presentation of single optokinetic or somatosensory stimuli. The visual analyzer was found to play a significant role in maintaining the upright position under natural gravity conditions in healthy children. A single exposure of the proprioceptive system to variable forces directed with the gravity of the earth (vertical) decreased the contribution of the visual analyzer. Healthy children maintained the upright position relying on the direction of movement of the optokinetic stimuli, which, however, produced no effect on the maintenance of posture in the patients. A hypothesis is proposed that prenatal or early postnatal CNS lesions decrease the contribution of phylogenetically newer brain structures to the regulation of upright posture.     

Spoilage of bottled red wine by acetic acid bacteria

AIMS: To determine the bacterial species associated with an outbreak of spoilage in commercially bottled red wine where the bottles had been stored in an upright vertical compared with horizontal position. METHODS AND RESULTS: Bottled wines comprising Cabernet Sauvignon, Pinot Noir, Shiraz, Merlot and blended red varieties were examined for visible spoilage. Analysis of visibly affected and non-affected wines revealed a spectrum of aroma and flavour defects, ranging from loss of fruity aroma, staleness, oxidized character to overt volatile acidity. Only acetic acid bacteria, and not yeast or lactic acid bacteria, could be isolated from both spoiled and unspoiled wines and were found to grow only on Wallerstein Nutrient (WL) medium supplemented with 10% red wine or 1-2% ethanol. Analysis of the 16S rRNA region and RAPD-PCR analysis showed the isolates to be a closely related group of Acetobacter pasteurianus, but this group was differentiated from the group comprising beer, vinegar and cider strains. CONCLUSIONS: A. pasteurianus was the species considered responsible for the spoilage but the isolates obtained had atypical properties for this species. In particular, they failed to grow on WL nutrient medium without ethanol or wine supplementation. Storage of the bottles of wine containing A. pasteurianus in an upright vertical position specifically induced growth and spoilage in a proportion of the bottles under conditions that were inhibitory for horizontally stored bottles. We hypothesize that the upright position created a heterogeneous environment that allowed the growth of bacteria in only those bottles sealed with cork closures that had upper limit for the natural permeability to oxygen. Such a heterogeneous environment would not exist in horizontally stored bottles as the larger volume of wine adjacent to the cork would strongly compete with the bacteria for the oxygen as it diffuses through the cork closure. SIGNIFICANCE AND IMPACT OF THE STUDY: A low level of bacteria (acetic acid bacteria) in wine can proliferate and cause wine spoilage in bottles stored in an upright vertical as opposed to an horizontal position under conditions that would normally limit bacterial development.     

Computer simulation on the cooperation of functional molecules during the early stages of evolution

It is very likely that life began with some RNA (or RNA-like) molecules, self-replicating by base-pairing and exhibiting enzyme-like functions that favored the self-replication. Different functional molecules may have emerged by favoring their own self-replication at different aspects. Then, a direct route towards complexity/efficiency may have been through the coexistence/cooperation of these molecules. However, the likelihood of this route remains quite unclear, especially because the molecules would be competing for limited common resources. By computer simulation using a Monte-Carlo model (with "micro-resolution" at the level of nucleotides and membrane components), we show that the coexistence/cooperation of these molecules can occur naturally, both in a naked form and in a protocell form. The results of the computer simulation also lead to quite a few deductions concerning the environment and history in the scenario. First, a naked stage (with functional molecules catalyzing template-replication and metabolism) may have occurred early in evolution but required high concentration and limited dispersal of the system (e.g., on some mineral surface); the emergence of protocells enabled a "habitat-shift" into bulk water. Second, the protocell stage started with a substage of "pseudo-protocells", with functional molecules catalyzing template-replication and metabolism, but still missing the function involved in the synthesis of membrane components, the emergence of which would lead to a subsequent "true-protocell" substage. Third, the initial unstable membrane, composed of prebiotically available fatty acids, should have been superseded quite early by a more stable membrane (e.g., composed of phospholipids, like modern cells). Additionally, the membrane-takeover probably occurred at the transition of the two substages of the protocells. The scenario described in the present study should correspond to an episode in early evolution, after the emergence of single "genes", but before the appearance of a "chromosome" with linked genes.     

Activity of respiratory muscles in upright and recumbent humans

It is established that during tidal breathing the rib cage expands more than the abdomen in the upright posture, whereas the reverse is usually true in the supine posture. To explore the reasons for this, we studied nine normal subjects in the supine, standing, and sitting postures, measuring thoracoabdominal movement with magnetometers and respiratory muscle activity via integrated electromyograms. In eight of the subjects, gastric and esophageal pressures and diaphragmatic electromyograms via esophageal electrodes were also measured. In the upright postures, there was generally more phasic and tonic activity in the scalene, sternocleidomastoid, and parasternal intercostal muscles. The diaphragm showed more phasic (but not more tonic) activity in the upright postures, and the abdominal oblique muscle showed more tonic (but not phasic) activity in the standing posture. Relative to the esophageal pressure change with inspiration, the inspiratory gastric pressure change was greater in the upright than in the supine posture. We conclude that the increased rib cage motion characteristic of the upright posture owes to a combination of increased activation of rib cage inspiratory muscles plus greater activation of the diaphragm that, together with a stiffened abdomen, acts to move the rib cage more effectively.     

Mode shift of an inhaled aerosol bolus is correlated with flow sequencing in the human lung.

We studied the effects on aerosol bolus inhalations of small changes in convective inhomogeneity induced by posture change from upright to supine in nine normal subjects. Vital capacity single-breath nitrogen washout tests were used to determine ventilatory inhomogeneity change between postures. Relative to upright, supine phase III slope was increased 33 +/- 11% (mean +/- SE, P < 0.05) and phase IV height increased 25 +/- 11% (P < 0.05), consistent with an increase in convective inhomogeneity likely due to increases in flow sequencing. Subjects also performed 0.5-microm-particle bolus inhalations to penetration volumes (V(p)) between 150 and 1,200 ml during a standardized inhalation from residual volume to 1 liter above upright functional residual capacity. Mode shift (MS) in supine posture was more mouthward than upright at all V(p), changing by 11.6 ml at V(p) = 150 ml (P < 0.05) and 38.4 ml at V(p) = 1,200 ml (P < 0.05). MS and phase III slope changes correlated positively at deeper V(p). Deposition did not change at any V(p), suggesting that deposition did not cause the MS change. We propose that the MS change results from increased sequencing in supine vs. upright posture.     

Evolution of seahorses' upright posture was linked to Oligocene expansion of seagrass habitats

Seahorses (Syngnathidae: Hippocampus) are iconic marine teleosts that are readily identifiable by their upright posture. The fossil record is inadequate to shed light on the evolution of this trait because it lacks transitional forms. There are, however, extant syngnathid species (the pygmy pipehorses) that look like horizontally swimming seahorses and that might represent a surviving evolutionary link between the benthic seahorses and other, free-swimming members of the family Syngnathidae. Using sequence data from five nuclear loci, we confirm the sister taxon relationship between seahorses and pygmy pipehorses. Molecular dating indicates that the two taxa diverged during the Late Oligocene. During this time, tectonic events in the Indo-West Pacific resulted in the formation of vast amounts of new shallow-water areas and associated expansion of seagrass habitats that would have favoured the seahorses’ upright posture by improving their camouflage while not affecting their manoeuvrability negatively. The molecular techniques employed here provide new insights into the evolution of a taxon whose fossil record is incomplete, but whose evolutionary history is so recent that the major stages of morphological evolution are still represented in extant species.     

Raising the sauropod neck: it costs more to get less

The long necks of gigantic sauropod dinosaurs are commonly assumed to have been used for high browsing to obtain enough food. However, this analysis questions whether such a posture was reasonable from the standpoint of energetics. The energy cost of circulating the blood can be estimated accurately from two physiological axioms that relate metabolic rate, blood flow rate and arterial blood pressure: (i) metabolic rate is proportional to blood flow rate and (ii) cardiac work rate is proportional to the product of blood flow rate and blood pressure. The analysis shows that it would have required the animal to expend approximately half of its energy intake just to circulate the blood, primarily because a vertical neck would have required a high systemic arterial blood pressure. It is therefore energetically more feasible to have used a more or less horizontal neck to enable wide browsing while keeping blood pressure low.     

Postural specificity of cardiovascular adaptations to exercise training

The purposes of this study were to determine 1) whether posture affects the magnitude of cardiovascular adaptations to training and 2) whether cardiovascular adaptations resulting from exercise training in the supine posture transfer (generalize) to exercise in the upright posture and vice versa. Sixteen sedentary men, aged 18-33 yr, were trained using high-intensity interval and prolonged continuous cycling in the supine (STG; supine training group) or upright (UTG; upright training group) posture 4 days/wk, 40 min/day, for 8 wk, while seven male subjects served as nontraining controls. After training, maximal O2 uptake measured during supine and upright cycling, respectively, increased significantly (P less than 0.05) by 22.9 and 16.1% in the STG and by 6.0 and 14.6% in the UTG. No significant cardiovascular adaptations were observed at rest. During submaximal supine cycling at 100 W, significant increases in end-diastolic volume (21%) and stroke volume (22%) (radionuclide ventriculography and CO2 rebreathing) and decreases in heart rate, blood pressure, and systemic vascular resistance occurred in the STG, whereas only a significant decrease in blood pressure occurred in the UTG. During upright cycling at 100 W, a significant decrease in blood pressure occurred in the STG, whereas significant increases in end-diastolic volume (17%) and stroke volume (18%) and decreases in blood pressure and systemic vascular resistance occurred in the UTG. Volume of myocardial contractility, ejection fraction, and systolic blood pressure-to-end-systolic volume ratio did not change significantly after training when measured during supine and upright cycling in either training group. Blood volume increased significantly in the UTG but remained unchanged in the STG.(ABSTRACT TRUNCATED AT 250 WORDS)     

Balance of the head in hominid evolution

In primates it is useful to distinguish three basic types of bipedal posture: (1) agonial, with extended hips and knees as in modern humans, (2) monogonial, with flexed hips but extended knees. and (3) digonial, with flexed hips and knees as in pongids. Early hominids retained an ancestral, forwardly inclined posture of the neck and head. Therefore the body posture of australopithednes must have differed from that in modem man, in which the centre of gravity of the head can be aligned with that of the body, other major centra of gravity, and important axes of rotation in a single frontal plane. It is suggested that in australopithednes the gravitational tilt of the head was counterbalanced by bent hips in association with hyperextended knees (monogonial posture). In australopithecines the increase in brain weight would have counteracted an improvement in the balance of the head. After the neck had assumed a more vertical posture as a consequence of shortening of the face, selection for an improved balance system in the bipedal posture favoured an increase in the weight of the postcondylar portion of the head, accentuated by selection for a posterior shift of the superior nuchal line in order to minimise the force of the nuchal muscles. At this stage the evolutionary increase in brain weight may have been largely a by-product of the process towards perfecting the bipedal posture. When the centre of gravity of the head had first become aligned with that of the body, the conditions of balance of the head had become favourable for a dramatic increase of brain size, as a result of selection for greater learning and storage capacity of the brain.