Flower symmetry and shape in Antirrhinum

According to their symmetry, flowers are classified as radially symmetrical or bilaterally symmetrical. Bilateral symmetry, which is thought to have evolved from radial symmetry, results from establishment of asymmetry relative to a dorsoventral axis of flowers. Here we consider developmental genetic mechanisms underlying the generation of this asymmetry and how they relate to controls of petal shape and growth in Antirrhinum. Two genes, CYC and DICH, are expressed in dorsal domains of the Antirrhinum flower and determine its overall dorsoventral asymmetry and the asymmetries and shapes of individual floral organs, by influencing regional growth. Another gene, DIV, influences regional asymmetries and shapes in ventral regions of the flower through a quantitative effect on growth. However, DIV is not involved in determining the overall dorsoventral asymmetry of the flower and its effects on regional asymmetries depend on interactions with CYC/DICH. These interactions illustrate how gene activity, symmetry, shape and growth may be related.     

Stabilization of human standing posture using functional neuromuscular stimulation

Functional neuromuscular stimulation (FNS)/functional electrical stimulation (FES) is a potential way to restore some functionality to the limbs of patients with spinal cord injury through direct/indirect stimulation of the motoneuron. One of the constraints for wider use of FNS on paraplegic patients is the lack of efficient control algorithm. Most of the published works on FNS/FES control are based on oversimplified models of human body dynamics. An innovative control strategy for stabilizing the standing posture of paraplegic patients is proposed here which is a combination of a proportional-plus-derivative controller for motions of the skeletal system and a control action prediction mechanism to produce musculotendon activation. The goal is to produce musculotendon torque which can approximate those demanded by the controller for the skeletal system. In computer simulations, using a detailed skeletal–musculotendon–muscle activation dynamics model of human body, this FNS/FES control approach can stabilize a paraplegic patient's standing posture with the minimum number of musculotendon groups. Also, it is found that this control strategy can maintain stability even in the presence of reasonable variations in the controller's musculotendon parameters.     

Support surface related changes in feedforward and feedback control of standing posture

The aim of the study was to investigate the effect of different support surfaces on feedforward and feedback components of postural control. Nine healthy subjects were exposed to external perturbations applied to their shoulders while standing on a rigid platform, foam, and wobble board with eyes open or closed.Electrical activity of nine trunk and leg muscles and displacements of the center of pressure were recorded and analyzed during the time frames typical of feedforward and feedback postural adjustments. Feedforward control of posture was characterized by earlier activation of anterior muscles when the subjects stood on foam compared to a wobble board or a firm surface. In addition, the magnitude of feedforward muscle activity was the largest when the foam was used. During the feedback control, anterior muscles were activated prior to posterior muscles irrespective of the nature of surface. Moreover, the largest muscle activity was seen when the supporting surface was foam. Maximum CoP displacement occurred when subjects were standing on a rigid surface.Altering support surface affects both feedforward and feedback components of postural control. This information should be taken into consideration in planning rehabilitation interventions geared towards improvement of balance.     

Differences between two subgroups of low back pain patients in lumbopelvic rotation and symmetry in the erector spinae and hamstring muscles during trunk flexion when standing

The present study was performed to examine lumbopelvic rotation and to identify asymmetry of the erector spinae and hamstring muscles in people with and without low back pain (LBP). The control group included 16 healthy subjects, the lumbar-flexion–rotation syndrome LBP group included 17 subjects, and the lumbar-extension–rotation syndrome LBP group included 14 subjects. Kinematic parameters were recorded using a 3D motion-capture system, and electromyography parameters were measured using a Noraxon TeleMyo 2400T. The two LBP subgroups showed significantly more lumbopelvic rotation during trunk flexion in standing than did the control group. The muscle activity and flexion–relaxation ratio asymmetries of the erector spinae muscles in the lumbar-flexion–rotation syndrome LBP group were significantly greater than those in the control group, and the muscle activity and flexion–relaxation ratio asymmetry of the hamstring muscles in the lumbar-extension–rotation syndrome LBP group were significantly greater than those in the control group. Imbalance or asymmetry of passive tissue could lead to asymmetry of muscular activation. Muscle imbalance can cause asymmetrical alignment or movements such as unexpected rotation. The results showed a greater increase in lumbopelvic rotation during trunk flexion in standing among the lumbar-flexion–rotation syndrome and lumbar-extension–rotation syndrome LBP groups compared with the control group. The differences between the two LBP subgroups may be a result of imbalance and asymmetry in erector spinae and hamstring muscle properties.     

Initial cardiovascular response on change of posture from squatting to standing

The immediate cardiovascular responses on active change from the squatting (control) to the standing position differ from those obtained in the lying-to-standing manoeuvre. Without exception, the first beat after changing from squatting to standing showed a decrease in systolic, diastolic and mean pressure by 2.0 +/- 1.1 kPa (14.6 +/- 8.3 mm Hg), 1.4 +/- 1.7 kPa (10.6 +/- 12.6 mm Hg) and 1.9 +/- 1.0 kPa (13.9 +/- 7.3 mm Hg), respectively. During the 4th or 5th pulse after standing the pulse pressure was significantly higher than when lying (P less than 0.01). Mean pressure reached a minimum of 7.7 +/- 1.9 kPa (57.8 +/- 14.4 mm Hg) after 7.1 +/- 1.1 s. Thereafter the blood pressure increased to a new level within about 15 s. 11 of 16 subjects demonstrated a biphasic heart rate (HR) response. The maximum HR was reached after 11.0 +/- 2.4 s of standing. In all experiments, the peaks in HR were distinctly delayed after the blood pressure dips. We conclude that an arterial baroreflex could be implicated in the immediate HR increase after a squatting-to-standing manoeuvre. The subsequent time course of the initial HR response, however, might be induced by other mechanisms.     

Effects of standing vs. seated posture on repeated Wingate performance

Standing during cycling may increase overall muscular activity. However, effects of standing vs. seated posture on performance measures during repeated bouts have not been extensively explored. The purpose of this study was to examine the effects of standing vs. seated posture on repeated Wingate performance. Healthy volunteers (n = 35) performed 3 consecutive Wingate anaerobic power tests (W(1), W(2), W(3)) in a standing (STA) as well as seated (SIT) posture. Within-group comparisons were made for peak power, mean power, minimum power, and fatigue index. Results were considered significant at p < or = 0.05. No significant differences were found for peak power in W(1), W(2), or W(3). No significant difference was found for mean power in W(1) or W(2), but significant differences were found for mean power in W(3) (STA: 451.5 +/- 105.3, SIT: 425.7 +/- 110.0); minimum power in W(1) (STA: 433.6 +/- 100.8, SIT: 381.5 +/- 96.9), W(2) (STA: 348.1 +/- 112.9, SIT: 308.0 +/- 95.8), W(3) (STA: 292.0 +/- 103.6, SIT: 265.3 +/- 90.8); and fatigue index: W(1) (STA: 51.3 +/- 10.7, SIT: 56.9 +/- 9.3), W(2) (STA: 56.5 +/- 12.6, SIT: 61.8 +/- 12.2), W(3) (STA: 59.4 +/- 13.1, SIT: 63.6 +/- 12.4). Results suggest that a standing posture enhances performance during repeated Wingate cycling. The enhancement is most likely due to an attenuated loss in power, which in turn improves fatigue index.     

The effects of an attentional demand tasks on standing posture control

The present study sought to determine if the postural sway of a subject required to grasp a tray (motor task) holding a cup filled with water and prevent spilling (mental task), would be reduced by consciously redirecting attention to maintain the tray in a horizontal position. We hypothesized the mental task would increase the stabilization of standing postural balance. Postural sway was measured in 17 normal subjects under the following conditions: 1) holding a 100 g weight in each hand (total 200 g; no mental task), 2) holding with both hands a tray on which 200 g was placed (tray-holding task), and 3) holding with both hands a tray on which a cup filled with water weighing 200 g was placed in the center (mental task). Postural sway was significantly reduced during the mental task versus other tasks. Standing posture balance was stabilized when a mental task was added. Thus, we concluded that higher brain functions such as attention and consciousness exerted a significant influence over the control of standing posture.     

Scintigraphic evaluation of shape of lung and chest in upright and head-down posture

We determined the configuration of lungs and chest in six healthy young subjects using anteroposterior and lateral technetium-99m-labeled scintigraphic images obtained in upright and in 90 degree head-down posture at 0, 25, 50, 75, and 100% vital capacity (VC). The lung shape was evaluated from curves relating vertical height vs. cumulative volume of 20 apicodiaphragmatic lung zones of equal height. S-shaped curves were obtained, which, after size normalization, were largely independent of volume or posture (P greater than 0.1). However, the apical zones tended to become relatively wider and the diaphragmatic zones relatively smaller with increasing volume, especially between 0 and 25% VC in upright posture and 0-50% VC in head-down posture. Changing posture from upright to head-down also tended to slightly widen the apical zones and to narrow the diaphragmatic zones, which is in line with a greater intrathoracic penetration of the diaphragm/abdomen. The shape of the chest was evaluated from the ratio of the transverse-thoracic and anteroposterior distances over height. These ratios did not clearly change with posture (P greater than or equal to 0.05) but increased by approximately 30% with decreasing volume (P less than 0.01). The fact that these shape changes of the chest were not accompanied by similar changes in lung shape can be explained mainly by widening of the mediastinum when volume decreases. In conclusion, the shape of the lung and chest are similar in head-down and upright humans, in contrast to the reversal of the apicodiaphragmatic differences in alveolar expansion and in transpulmonary pressure.     

Enhanced stretch reflex excitability in the soleus muscle during passive standing posture in humans

The purpose of this study was to test whether the spinal reflex excitability of the soleus muscle is modulated as posture changes from a supine to a passive upright position. Eight healthy subjects (29.6 ± 5.4 yrs) participated in this study. Stretch and H-reflex responses were elicited while the subjects maintained passive standing (ST) and supine (SP) postures. The passive standing posture was accomplished by using a gait orthosis to which a custom-made device was mounted to elicit stretch reflex in the soleus muscle. This orthosis makes it possible to elicit stretch and H-reflexes without background muscle activity in the soleus muscle. The results revealed that the H-reflex amplitude in the ST was smaller than that in the SP condition, which is in good agreement with previous reports. On the other hand, the stretch reflex was significantly larger in the ST than in the SP condition. Since the experimental conditions of both the stretch and H-reflex measurements were exactly the same, the results were attributed to differences in the underlying neural mechanisms of the two reflex systems: different sensitivity of the presynaptic inhibition onto the spinal motoneuron pool and/or a change in the muscle spindle sensitivity.     

A method for analysis of back shape in scoliosis

The shape of the back is an important factor in the clinical assessment of various spinal disorders, in particular scoliosis. A method of analysis of back surface shape is described which was designed to present most of the numerical parameters needed to assess the progress of the disease as it affects body shape. Measurements of back surface shape and manually marked anatomical landmarks were taken from a television/computer surface measurement system in which a plane of light was scanned over the back and from moiré topographs. The anatomical landmarks were used to define reference planes from which successive analyses were matched. Asymmetry in the transverse plane was illustrated by horizontal cross-sections and skin surface angles. The lateral deformity was shown by an estimate of the line of the vertebral bodies beneath the skin, derived by adding an extra lateral displacement to the palpated positions of the spinous processes, proportional to the rotation of the skin in the transverse plane. This model was used to estimate vertebral end-plate angles and Cobb angles. Lateral sections showed kyphosis and lordosis. Correlations of Lateral Asymmetry from the surface shape analysis with Cobb angle from X-ray measurements in three groups of patients (totalling 119 subjects) were in the range r = 0.77 to r = 0.94, p less than 0.0001. The analysis has reduced follow-up X-ray examinations at the Nuffield Orthopaedic Centre because it indicates quantitatively and with complete safety both lateral asymmetry and deformity in the transverse plane.     

Effects of 20 days horizontal bed rest on maintaining upright standing posture in young persons

The effects of 20 days horizontal bed rest (BR) on postural reflex were studied by measuring fluctuation of center of gravity in the body during two legs or one leg upright standing in 10 young volunteers. The fluctuation was decided as total moving distance of the center recorded during 60sec standing on a force plate. The stability was measured by the moved area. After BR, the moving distance increased during two legs standing with open eyes (p<0.05), but statistically unchanged with closed eyes. The moving area decreased during right one-leg standing with closed eyes (p<0.05), but unchanged during left one-leg standing. Despite with open eyes the increased distance suggested that postural reflexes to maintain upright position were probably decreased by increased unsuitable feedback informations from the visual receptor deconditioning during BR. The decreased area during right one-leg standing with closed eyes also suggested that the declined standing posture reflex was probably related to more rapidly lowered functions for maintaining standing position in the dominating leg than in the other.     

Role of trunk muscles in generating follower load in the lumbar spine of neutral standing posture

Recently, experimental results have demonstrated that the load carrying capacity of the human spine substantially increases under the follower load condition. Thus, it is essential to prove that a follower load can be generated in vivo by activating the appropriate muscles in order to demonstrate the possibility that the stability of the spinal column could be maintained through a follower load mechanism. The aim of this study was to analyze the coordination of the trunk muscles in order to understand the role of the muscles in generating the follower load. A three-dimensional finite element model of the lumbar spine was developed from T12 to S1 and 117 pairs of trunk muscles (58 pairs of superficial muscles and 59 pairs of deep muscles) were considered. The follower load concept was mathematically represented as an optimization problem. The muscle forces required to generate the follower load were predicted by solving the optimization problem. The corresponding displacements and rotations at all nodes were estimated along with the follower forces, shear forces, and joint moments acting on those nodes. In addition, the muscle forces and the corresponding responses were investigated when the activations of the deep muscles or the superficial muscles were restricted to 75% of the maximum activation, respectively. Significantly larger numbers of deep muscles were involved in the generation of the follower load than the number of superficial muscles, regardless of the restriction on muscle activation. The shear force and the resultant joint moment are more influenced by the change in muscle activation in the superficial muscles. A larger number of deep trunk muscles were activated in order to maintain the spinal posture in the lumbar spine. In addition, the deep muscles have a larger capability to reduce the shear force and the resultant joint moment with respect to the perturbation of the external load or muscle fatigue compared to the superficial muscles.     

The effect of various degrees of foot posture on standing balance in a healthy adult population

Abstract

Purpose: Foot biomechanics plays a significant role in the quality of standing and walking. It has been believed that even minor biomechanical alterations in the foot support surface may influence strategies to maintain body standing balance. Hence, the aim of this study was to investigate the role of various degrees of foot posture on static and dynamic standing balance components in a healthy adult population.

Subjects and methods: A convenience sample of 41 healthy adult subjects with a mean age of 24.3?±?6.4 years and a body mass index (BMI) of 29?kg/m² participated in this study. On the basis of foot posture index (FPI), the participants were allocated into either group A or B. Group A included 16 subjects with an FPI range of 6–11 whereas group B included 25 subjects with an FPI range of 0–5. Standing balance components were analyzed using computerized dynamic posturography (CDP) by the Modified Clinical Test of Sensory Interaction on Balance (mCTSIB) and the limit of stability (LOS).

Results: Spearman’s correlation coefficient showed a significant correlation between the standing dynamic balance and FPI in group B but not in group A. Moreover, it also showed no significant correlation between the standing static balance component and FPI in either group A or B.

Conclusion: This study concluded that higher degrees of FPI might have an effect on standing dynamic balance in healthy subjects. These components may require extra attention during the preventive aspects of rehabilitation.     

The impact of localized fatigue on contralateral tremor and muscle activity is exacerbated by standing posture

Physiological tremor is an inherent feature of the motor system that is influenced by intrinsic (neuromuscular) and/or extrinsic (task) factors. Given that tremor must be accounted for during the performance of many fine motor skills; there is a requirement to clarify how different factors interact to influence tremor. This study was designed to assess the impact localized fatigue of a single arm and stance position had on bilateral physiological tremor and forearm muscle activity. Results demonstrated that unilateral fatigue produced bilateral increases in tremor and wrist extensor activity. For example, fatigue resulted in increases in extensor activity across both exercised (increased 8–10% MVC) and the non-exercised arm (increased 3–7% MVC). The impact of fatigue was not restricted to changes in tremor/EMG amplitude, with altered hand–finger coupling observed within both arms. Within the exercised arm, cross-correlation values decreased (pre-exercise r = 0.62–0.64; post-exercise r = 0.37–0.43) while coupling increased within the non-exercised arm (pre-exercise r = 0.51–0.55; post-exercise r = 0.62–0.67). While standing posture alone had no significant impact on tremor/EMG dynamics, the tremor and muscle increases seen with fatigue were more pronounced when standing. Together these results demonstrate that the combination of postural and fatigue factors can influence both tremor/EMG outputs and the underlying coordinative coupling dynamics.     

3D Morphometric and posture study of felid scapulae using statistical shape modelling

We present a three dimensional (3D) morphometric modelling study of the scapulae of Felidae, with a focus on the correlations between forelimb postures and extracted scapular shape variations. Our shape modelling results indicate that the scapular infraspinous fossa becomes larger and relatively broader along the craniocaudal axis in larger felids. We infer that this enlargement of the scapular fossa may be a size-related specialization for postural support of the shoulder joint.