The relationship between lumbopelvic flexibility and sitting posture in adult women

Clinical observations have suggested that limited hamstring flexibility may be associated with sagittal spinal curvatures in spine flexed postures. Thus, limited hamstring flexibility may be related to large amounts of spine flexion in “slumped” sitting postures which could contribute to low back pain and injury. The aim of this study was to determine if hamstring and pelvic flexibility are associated with flexed sitting postures using a backless office chair. Forty-one healthy female adults aged 18–69 years were recruited. Subjects performed the Sit-and-Reach test to determine maximum flexibility values and lumbar and pelvic angles were measured with accelerometers. Participants then completed a standardized typing task for a 10-minute sitting trial at an ergonomically adjusted workstation. The results showed no association between hamstring flexibility and seated lumbar spine and pelvic angles (p = 0.999, η² = 0.000; p = 0.901, η² = 0.006). Greater pelvic flexibility was associated with a more upright lumbar sitting posture (p = 0.023; η² = 0.132) but with no specific pelvic sitting posture (p = 0.660; η² = 0.005). Different movement strategies during the Sit-and-Reach test were detected: all participants moved through their lumbar spine; but only those with ‘excellent’ flexibility also used their pelvis. Individuals in the ‘excellent’ flexibility group were significantly shorter than those with ‘poor’ and ‘good’ flexibility (p = 0.020; η² = 0.190). In conclusion, hamstring flexibility does not influence sitting posture but pelvic flexibility does. Other factors such as acetabulofemoral joint limitations, consciousness of posture, or the seat itself may also influence sitting posture. Different movement strategies as well as height appear to contribute to the Sit-and-Reach test which should be researched further.     

Position sense in the lumbar spine with torso flexion and loading

Proprioception plays an important role in appropriate sensation of spine position, movement, and stability. Previous research has demonstrated that position sense error in the lumbar spine is increased in flexed postures. This study investigated the change in position sense as a function of altered trunk flexion and moment loading independently. Reposition sense of lumbar angle in 17 subjects was assessed. Subjects were trained to assume specified lumbar angles using visual feedback. The ability of the subjects to reproduce this curvature without feedback was then assessed. This procedure was repeated for different torso flexion and moment loading conditions. These measurements demonstrated that position sense error increased significantly with the trunk flexion (40%, p < .05) but did not increase with moment load (p = .13). This increased error with flexion suggests a loss in the ability to appropriately sense and therefore control lumbar posture in flexed tasks. This loss in proprioceptive sense could lead to more variable lifting coordination and a loss in dynamic stability that could increase low back injury risk. This research suggests that it is advisable to avoid work in flexed postures.     

X射线对仔鼠皮肤组织结构及c-Fos、KGF表达的影响

应用生物显微技术和免疫组织化学方法,研究了不同剂量X射线(0.0、3.5、6.5 Gy)辐射对发育期(1、5、10和20 d)昆明小鼠(Mus musculus)仔鼠皮肤组织结构和c-Fos、KGF表达的影响,探讨了c-Fos、KGF的生物活性作用及调控意义,并利用IPP专业图像分析软件对其表达强度进行定量分析.结果表...     

Rotational mobility of the human back in forward flexion

This paper describes the measurement of the ability of the human back to twist when in flexed postures using a new electromagnetic measurement device. The mobility of the lumbar spine in 12 normal male subjects was investigated and it was demonstrated that increased rotation was possible when in a flexed posture. This suggests that the intervertebral disc may be vulnerable to torsion when twisting is combined with sub-maximal sagittal flexion.     

In vivo measurement and mapping of skin redox stress induced by ultraviolet light exposure

Exposure of skin to UV light presents a potent oxidative stress and this could alter the skin redox state. In this context, we evaluated the ability of electron paramagnetic resonance (EPR) imaging to provide noninvasive in vivo mapping of the redox status of the skin of living rats. The redox status was measured using a topically applied nitroxyl spin probe, (15)N-PDT. The nitroxyl intensity profile obtained across the skin layers showed that the concentration of the probe was higher in the epidermis and lower in the dermis and hypodermis. Skin permeability and reduction metabolism were evaluated in the skin exposed to UVB (312 nm) radiation. Exposure of skin to UVB decreased the overall reduction rate constant of the nitroxyl probe to 25 +/- 6% of the value obtained in the untreated skin. EPR imaging data showed that after the UVB treatment, the reduction rate constant decreased to 41 +/- 1% in epidermis, 28 +/- 1% in dermis, and 21 +/- 8% in hypodermis layers. The data suggested that UVB decreased the overall reducing capability of the skin with a larger decrease in the dermis and hypodermis. In summary, in vivo EPR imaging measurements showed significant alterations in the redox state of the skin exposed to UV light.     

A biphasic multilayer computational model of human skin

The present study investigates the layer-specific mechanical behavior of human skin. Motivated by skin’s histology, a biphasic model is proposed which differentiates between epidermis, papillary and reticular dermis, and hypodermis. Inverse analysis of ex vivo tensile and in vivo suction experiments yields mechanical parameters for each layer and predicts a stiff reticular dermis and successively softer papillary dermis, epidermis and hypodermis. Layer-specific analysis of simulations underlines the dominating role of the reticular dermis in tensile loading. Furthermore, it shows that the observed out-of-plane deflection in ex vivo tensile tests is a direct consequence of the layered structure of skin. In in vivo suction experiments, the softer upper layers strongly influence the mechanical response, whose dissipative part is determined by interstitial fluid redistribution within the tissue. Magnetic resonance imaging-based visualization of skin deformation in suction experiments confirms the deformation pattern predicted by the multilayer model, showing a consistent decrease in dermal thickness for large probe opening diameters.

     

Load-sharing in the lumbosacral spine in neutral standing & flexed postures – A combined finite element and inverse static study

Understanding load-sharing in the spine during in-vivo conditions is critical for better spinal implant design and testing. Previous studies of load-sharing that considered actual spinal geometry applied compressive follower load, with or without moment, to simulate muscle forces. Other studies used musculoskeletal models, which include muscle forces, but model the discs by simple beams or spherical joints and ignore the articular facet joints.This study investigated load-sharing in neutral standing and flexed postures using a detailed Finite Element (FE) model of the ligamentous lumbosacral spine, where muscle forces, gravity loads and intra-abdominal pressure, as predicted by a musculoskeletal model of the upper body, are input into the FE model. Flexion was simulated by applying vertebral rotations following spine rhythm measured in a previous in-vivo study, to the musculoskeletal model. The FE model predicted intradiscal pressure (IDP), strains in the annular fibers, contact forces in the facet joints, and forces in the ligaments. The disc forces and moments were determined using equilibrium equations, which considered the applied loads, including muscle forces and IDP, as well as forces in the ligaments and facet joints predicted by the FE model. Load-sharing was calculated as the portion of the total spinal load carried along the spine by each individual spinal structure. The results revealed that spinal loads which increased substantially from the upright to the flexed posture were mainly supported by the discs in the upright posture, whereas the ligaments’ contribution in resisting shear, compression, and moment was more significant in the flexed posture.     

Skin penetration of infective hookworm larvae. I. The path of migration of infective larvae of Ancylostoma braziliense in canine skin

Migratory behaviour of Ancylostoma braziliense was studied in relation to the structure of the skin in dogs after primary infections. Data were obtained studying serial sections of lateral skin areas 6 mm in diameter, which had been exposed to larvae. The sections were stained either with Harris' haematoxylin and eosin or with P.A.S. or as outlined by Crossmon. Most of the larvae managed to penetrate the skin within 1/2 hr after the application. Hairs did not seem to constitute sites of entry. The larvae moved into the horny layer where edges of keratinized cells provide uneven spots. They migrated approximately parallel to the surface from the horny layer into the living epidermis and continued into an external root sheath of a hair follicle. They could only leave this site via sebaceous glands for the dermis or via apocrine sweat glands for the hypodermis. Tunnels from the epidermis into the dermis, however, suggested that a direct trans-epidermal migration had occurred. The vessels invaded by larvae were hypodermal lymphatic vessels. The first ones were found in these structures 1/2 h after the onset of the exposure.     

Cicatrization of the skin of the 7-day-old chick embryo cultured in vitro

A morphological study of in vitro wound healing has been performed by light, transmission and scanning electron microscopy in dorsal thoraco-lumbar skin of 7-day chick embryos. A circular wound, 750 microns in diameter, was punched out of dorsal skin, removing epidermis and the underlying dense dermis. Wound closure was completed within 96 to 120 hours. Feather bud development was not observed at the wound site. The epidermis began to migrate some 24 h after the wounding; the migration of peridermal cells preceded that of basal epidermal cells by some 12 hours. Mechanisms of the epidermal migration were similar to those observed in situ during wound healing of the integument in 5-day chick embryos (THEVENET, 1981), Superficial epithelization of bare dermis occurred as soon as 12 h after the injury. Cytoplasm of dermal cells exhibited many microtubules and a dilated rough endoplasmic reticulum. During the first 48 h, the epidermal cells established direct contacts and zones of close parallel apposition with epithelized dermal cell processes. The basement membrane lamina densa was maintained at the edges of the wound without retraction or ruffling. It was reconstituted concomitantly with the epidermal migration within 72 h. Cytoplasm of migratory epidermal and epithelized dermal cells exhibited many cytoskeleton structures.     

Reconstruction of the skin in three-dimensional collagen gel matrix culture

Summary The skin comprises three layers: epidermis, dermis, and hypodermis. We report here on a skin, reconstructed in vitro, that is composed of all three layers. The topmost layer, epidermis, was exposed to air by a new method. The exposure induced an extensive proliferation, and differentiation, i.e. keratinization was eventually observed in the cultured epidermal cells. Skin thus cultured will be a useful graft of transplantation and provide an ideal model system in which to study diseases of the skin.     

Crouched posture and high fulcrum, a principle in the locomotion of small mammals: The example of the rock hyrax (Procavia capensis) (Mammalia: Hyracoidea)

The cineradiographic study of the locomotion of the rock hyrax (Procavia capensis) and the functional interpretation of its locomotory system, reveals that the main action of proximal segments is combined with flexed position and low movements of limb joints. This observation can be applied to the locomotion of other small mammals. In the forelimb, scapular rotation and translation account for more than 60% of step length. Effective shoulder joint movements are mostly restricted to less than 20°, and elbow movements range mainly between 20°-50°. The detachment of the shoulder girdle of therian mammals from the axial skeleton, and development of a supraspinous fossa, are correlated with movements at a high scapular fulcrum. Movements at such a high fulcrum are in interdependency with a crouched posture. Only flexed limbs can act as shock absorbers and prevent vertical changes in the center of gravity. Basic differences in forelimb movements exist between larger primates (humeral retraction) and smaller mammals (scapula retraction). In the hyrax, propulsion is due mainly to hip joint movements in symmetrical gaits, but sagittal lumbar spine movements play the dominant role at in-phase gaits. Joint and muscular anatomy, especially of the shoulder region, are discussed in view of the kinematic data.     

雄性峨眉髭蟾“胡子”的组织结构特征

采用石蜡切片与苏木精-伊红染色及扫描电镜,对雄性峨眉髭蟾Leptobrachium boringii的角质刺及其周边皮肤进行了显微结构和亚显微结构的观察。显微结构观察发现,峨眉髭蟾的角质刺属于皮肤衍生物,突起呈倒"V"形。角质刺由表皮和真皮构成,表皮为复层扁平上皮,可分成4层;最外层细胞角质化,细胞轮廓不清,被染成深红色。真皮由疏松结缔组织构成,分辨不出致密层与疏松层,其内未见皮肤腺,但有少量色素细胞与毛细血管分布。表皮嵴伸入到真皮层,在以往的无尾两栖类研究中未见报道。角质刺基部可见皮肤褶翻起将其包裹在内,皮肤褶向上延伸形成角质刺。扫描电镜观察表明,角质刺顶端呈锥形的"小山丘"状,表面可分辨出表皮细胞轮廓,细胞为呈覆瓦状排列的角质化细胞。角质刺与皮肤交界处为多边形的角质化细胞。角质化上皮细胞的上表面与下表面均具有凹凸不平的花纹结构,细胞之间以镶嵌的方式连接。     

Morphological,immunohistochemical and ultrastructural characterization of the skin of turbot (Psetta maxima L.)

This study was undertaken to identify the normal morphologic, immunohistochemical and ultrastructural features of skin of the turbot (Psetta maxima L.). In the turbot skin, three morphologically distinct layers were identified: epidermis, dermis and hypodermis. The epidermis was non-keratinizing, stratified squamous epithelium that varies in thickness from 5 to 14 cells and 60 to 100 μm in size. Goblet cells were seen randomly distributed between malpighian cells in the epidermal layer. These mucous cells were mainly located in the upper third of the epidermis and displayed a spherical to elongated morphology. Dermis was divided in two well-differentiated layers, the superficial stratum laxum and the deeper stratum compactum. Hypodermis was a loose layer mainly composed by adipocytes but we could observe variable amounts of fibroblast, collagen and blood vessels. In turbot two pigmentary layers could be identified: the pigmentary layer of dermis was located between basement membrane and dermis and the pigmentary layer of hypodermis immediately above the muscular layer. Three different types of chromatophores were present: melanophores, iridophores and xanthophores. The main differences observed between groups of fish with different colouration were in the amount of melanophores and xanthophores. The purpose of this article is to provide an overview of normal cutaneous biology prior to consideration of specific cutaneous alterations and diseases in turbot.     

Ultrastructural and histochemical study on gills and skin of the Senegal sole, Solea senegalensis

This study was undertaken to identify the normal ultrastructural features of gills and skin of the Senegal sole, Solea senegalensis, for a comparative measure to morphological alterations caused by environmental stressors such as reduced water quality and diseases. In the Senegal sole skin, four morphologically distinct layers were identified: cuticle, epidermis, dermis and hypodermis. The epidermis was composed of stratified epithelium containing three cellular layers: the outermost or mucosa layer, the middle or fusiform layer and the stratum germinativum or the basal layer. In the mucosa, two mucous cell types were differentiated: type A cells containing several round vesicles of different electron density and type B cells containing mucosomes of uniform electron density. Senegal sole have five pairs of gill arches, each containing two rows of well‐developed and compactly organized primary filaments and secondary lamellae. Fingerprint‐like microridges were observed on the surface of epithelial cells. The branchial lamellae epithelium consisted of different cell types: pavement, mucous and chloride. Between the chloride cells and the larger pavement cells, accessory cells were observed. Complexes of tight junctions and desmosomes were frequently observed between adjacent chloride and epithelial cells. Neutral mucosubstances and/or glycoconjugates were observed in the epidermis, dermis and hypodermis of S. senegalensis skin. Proteins rich in different amino acids, such as arginine and cysteine, reacted negatively or weakly positive in the epidermis, dermis and hypodermis. In gills, some mucous cells responded weakly positive to periodic acid‐Schiff (PAS) reaction but were strongly stained with Alcian Blue at pH 0.5, 1 and 2.5. When Alcian Blue pH 2.5–PAS reaction was performed, most mucous cells were stained blue (carboxylated mucins) and some mucocytes stained purple, indicating a combination of neutral and acid mucins. Proteins rich in cysteine‐bound sulphydryl (‐SH‐) and cystine disulphide (‐S‐S‐) groups were strongly detected in branchial and epidermal mucous cells, whereas lysine, tyrosine and arginine containing proteins showed very weak staining in both epidermal and branchial mucous cells. Protein reactions were strongly positive in the pillar cells, except for those rich in tryptophan, whereas the branchial cartilaginous tissue did not show an important reaction. The performed lipid reactions were negative in goblet and chloride cells. It is concluded from this study that ultrastructural and cytohistochemical features of the Senegal sole skin and gills may serve as control structures in both natural and aquaculture systems to monitor or detect environmental stress responses at the histological level.     

Prenatal development of the integument in Delphinidae (Cetacea: Odontoceti)

The prenatal development of epidermis, dermis, and hypodermis was studied in embryos of different ago of two delphinid species (Stenella attenuata, Delphinus delphis), using light and transmission electron microscopical methods. The delphinid embryo is covered by a multilayered tissue formed by four different epidermal generations (periderm, stratum intermedium-I, str. intermedium-II, str. spinosum) produced by the str. basale. The first layer appears at about 40–50 mm of body length, the second type (s.i.-I) about 60–160 mm, and the third type (s.i.-II) is present at 160–500 mm. The first spinosal cells are produced at 225–260 mm body length; thenceforth, the epidermis increases continuously in thickness. Epidermal ridge formation begins about 400–mm body length. The development of the dermis is characterized by the early production of thin connective tissue fibers (40- 70-mm body length) and simultaneously the cutaneuous muscle matures in structure. Vascular development intensifies between embryos of 150–225 mm, and collagen production increases markedly in fetuses of 225–260-mm length. These events are paralledled by an increase in dermal thickness. The first elastic fibers can be recognized in the skin from the abdomen at about 600-mm body length. The development of the hypodermis is marked by very rapid and constantly progressing growth, beginning about 60-mm body length. The first typical fat cells appear in animals of 360–400 mm. Regional differences are obvious for all skin layers with regard to the flippers, where structural maturation proceeds more rapidly than in dorsal or abdominal regions. © 1995 Wiley-Liss, Inc.     

A variation of pigmentation in the glabrous skin of dogs

The usual pigmentation pattern in mammalian skin consists of fixed melanocytes in the basal layer of the epidermis, supplying keratinocytes with melanosomes. We observed that the glabrous skin (rhinaria and footpads) of dogs deviates from this pattern. In dogs, melanocytes are found in both the dermis and epidermis. The epidermal melanocytes are situated in the intercellular spaces of the basal and spinous layers. They are characterized by a quantity of cytoplasm containing a centriole, also developing melanosomes, and in some cases annulate lamellae. There is a high frequency of closely apposed melanocytes in the epidermis. Melanosomes in different stages of formation are also abundant. The morphology of the glabrous skin of dogs suggests transport of melanocytes from the dermis into the epidermis and formation of melanosomes in the epidermis. A distributed and intense pigment formation may be necessary to achieve the black noses of many dog breeds and wild canids, as well as dark footpads despite heavy abrasion and rapid skin renewal.     

Seated whole body vibrations with high-magnitude accelerations--relative roles of inertia and muscle forces

Reliable computation of spinal loads and trunk stability under whole body vibrations with high acceleration contents requires accurate estimation of trunk muscle activities that are often overlooked in existing biodynamic models. A finite element model of the spine that accounts for nonlinear load- and direction-dependent properties of lumbar segments, complex geometry and musculature of the spine, and dynamic characteristics of the trunk was used in our iterative kinematics-driven approach to predict trunk biodynamics in measured vehicle's seat vibrations with shock contents of about 4g (g: gravity acceleration of 9.8m/s(2)) at frequencies of about 4 and 20Hz. Muscle forces, spinal loads and trunk stability were evaluated for two lumbar postures (erect and flexed) with and without coactivity in abdominal muscles. Estimated peak spinal loads were substantially larger under 4Hz excitation frequency as compared to 20Hz with the contribution of muscle forces exceeding that of inertial forces. Flattening of the lumbar lordosis from an erect to a flexed posture and antagonistic coactivity in abdominal muscles, both noticeably increased forces on the spine while substantially improving trunk stability. Our predictions clearly demonstrated the significant role of muscles in trunk biodynamics and associated risk of back injuries. High-magnitude accelerations in seat vibration, especially at near-resonant frequency, expose the vertebral column to large forces and high risk of injury by significantly increasing muscle activities in response to equilibrium and stability demands.     

Model and in vivo studies on human trunk load partitioning and stability in isometric forward flexions

To resolve the trunk redundancy to determine muscle forces, spinal loads, and stability margin in isometric forward flexion tasks, combined in vivo-numerical model studies was undertaken. It was hypothesized that the passive resistance of both the ligamentous spine and the trunk musculature plays a crucial role in equilibrium and stability of the system. Fifteen healthy males performed free isometric trunk flexions of approximately 40 degrees and approximately 65 degrees +/- loads in hands while kinematics by skin markers and EMG activity of trunk muscles by surface electrodes were measured. A novel kinematics-based approach along with a nonlinear finite element model were iteratively used to calculate muscle forces and internal loads under prescribed measured postures and loads considered in vivo. Stability margin was investigated using nonlinear, linear buckling, and perturbation analyses under various postures, loads and alterations in ligamentous stiffness. Flexion postures significantly increased activity in extensor muscles when compared with standing postures while no significant change was detected in between flexed postures. Compression at the L5-S1 substantially increased from 570 and 771 N in upright posture, respectively, for +/-180 N, to 1912 and 3308 N at approximately 40 degrees flexion, and furthermore to 2332 and 3850 N at approximately 65 degrees flexion. Passive ligamentous/muscle components resisted up to 77% of the net moment. In flexion postures, the spinal stability substantially improved due both to greater passive stiffness and extensor muscle activities so that, under 180 N, no muscle stiffness was required to maintain stability. The co-activity of abdominal muscles and the muscle stiffness were of lesser concern to maintain stability in forward flexion tasks as compared with upright tasks. An injury to the passive system, on one hand, required a substantial compensatory increase in active muscle forces which further increased passive loads and, hence, the risk of injury and fatigue. On the other hand, it deteriorated the system stability which in turn could require greater additional muscle activation. This chain of events would place the entire trunk active-passive system at higher risks of injury, fatigue and instability.     

DDR1 and DDR2 in skin

ABSTRACT

DDR1 and DDR2 are expressed in skin but their expression differs according to the skin compartment, epidermis, dermis, hypodermis and to the embryonic origin of the cells. In skin, it seems that during physiological processes such as wound healing or pathological processes such as tumorigenesis or systemic sclerosis development only one of the DDR is dysregulated. Furthermore, the altered DDR in pathological process is not necessarily the DDR implicated in basal homeostasis. Indeed, in epidermis, while DDR1 is the main DDR involved in melanocyte homeostasis, DDR2 seems to be the main DDR implicated in melanoma. On the contrary, in dermis, while DDR2 is necessary for normal wound healing, dysregulation of DDR1 is associated with abnormal wound healing leading to keloid. In conclusion, targeting DDR could be a therapeutic solution, however side effects have to be managed carefully.     

The neutral posture of the cervical spine is not unique in human subjects

Cervical spine injuries often happen in dynamic environments (e.g., sports and motor vehicle crashes) where individuals may be moving their head and neck immediately prior to impact. This motion may reposition the cervical vertebrae in a way that is dissimilar to the upright resting posture that is often used as the initial position in cadaveric studies of catastrophic neck injury. Therefore our aim was to compare the “neutral” cervical alignment measured using fluoroscopy of 11 human subjects while resting in a neutral posture and as their neck passed through neutral during the four combinations of active flexion and extension movements in both an upright and inverted posture. Muscle activation patterns were also measured unilaterally using surface and indwelling electromyography in 8 muscles and then compared between the different conditions. Overall, the head posture, cervical spine alignment and muscle activation levels were significantly different while moving compared to resting upright. Compared to the resting upright condition, average head postures were 6–13° more extended, average vertebral angles varied from 11° more extended to 10° more flexed, and average muscle activation levels varied from unchanged to 10% MVC more active, although the exact differences varied with both direction of motion and orientation. These findings are important for ex vivo testing where the head and neck are statically positioned prior to impact – often in an upright neutral posture with negligible muscle forces – and suggest that current cadaveric head-first impact tests may not reflect many dynamic injury environments.