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Oculomotor research shows that eye movements are primed toward the midpoint of an array of visual stimuli, such that an eye movement to a visual target is executed most rapidly when it appears near the midpoint of an earlier array. At longer intervals between the prime and target, this facilitatory effect can reverse to become inhibitory - such that eye movements are slower when made toward the midpoint - but the source of this inhibition is unclear. One of our prior studies suggests a global source: target proximity to the midpoint determines inhibition, consistent with the notion that oculomotor activation is responsible for the effect and the original definition of inhibition of return. A later study suggests a local source: target proximity to the nearest array element determines inhibition, consistent with the notion that repeat stimulation of an input pathway is responsible. To resolve the ambiguity we systematically test whether timing differences between studies altered the source of the inhibition. We find that both previously observed patterns are reproducible depending on the prime offset - target onset asynchrony. We also resolve the discrepancy by showing that when this asynchrony is less than 200 ms, target proximity to the array's midpoint and its proximity to any given array element can jointly determine inhibition, whereas when the asynchrony is approximately 200 ms, inhibition is robust at the midpoint of the array. At longer asynchronies, all inhibitory effects rapidly dissipate. [ABSTRACT FROM AUTHOR]

• Analytical optical field of a cosh-Airy beam in uniaxial crystals is derived. • The centre of gravity, the beam spot size, and the linear momentum are derived. • The influence of the uniaxial crystal on the cosh-Airy beam is investigated. • The effect of the cosh part on the cosh-Airy beam is also investigated. • The propagation properties of the cosh-Airy beam are shown to be abundant. Analytical optical field of a cosh-Airy beam propagating in uniaxial crystals orthogonal to the optical axis is presented. Analytical expressions of the centre of gravity, the beam spot size, and the linear momentum for the cosh-Airy beam in uniaxial crystals are also derived, respectively. The propagation properties of a cosh-Airy beam are numerically demonstrated in the uniaxial crystal. The cosh-Airy beam still has the feature of self-acceleration in the two transverse directions. However, the cosh-Airy beam in the y -direction accelerates more slowly than that in the x -direction. The centre of gravity and the beam spot size in the y -direction are always less than those in the x -direction. The influence of the uniaxial crystal on the intensity distribution, the phase distribution, the centre of gravity, the beam spot size, and the linear momentum of a cosh-Airy beam is investigated. The effect of the cosh part on the centre of gravity, the beam spot size, and the linear momentum is also studied in detail. The centre of gravity of the cosh-Airy beam is less than that of the corresponding Airy beam. However, the beam spot size and the linear momentum of the cosh-Airy beam are larger than those of the corresponding Airy beam. [ABSTRACT FROM AUTHOR]

Restoring the ability to walk with a prosthesis is considered a fundamental rehabilitation goal after transfemoral amputation. An essential prerequisite for achieving this goal is adequate force transmission between the prosthesis and the body. Does bone anchorage of an artificial limb permit a more normal force transmission? Data of 15 healthy subjects, nine amputees fitted with bone-anchored prostheses, nine amputees using socket prostheses, and 18 patients with a total hip replacement were included in this multicenter, observational study. Ground reaction force was measured using Kistler force plates. Kinematics was recorded with 12 Vicon Bonita cameras. Subjects were instructed to walk at three different speeds: first at their self-selected, then at slow, and finally at fast speed. Self-selected walking speeds of subject groups were significantly different, osseointegrated amputees walked the slowest. The lowest ground reaction force was measured for osseointegrated amputees on the prosthetic side, who also showed the highest force on their contralateral side. Patients with hip replacements showed values similar as healthy subjects. The vertical center of gravity movement was specific for each subject group. The force transmission capacity of the bone-anchored prosthetic leg is limited during walking and is lower than both in socket prostheses users without symptoms and patients with total hip replacement. Therefore, active amputees well fitted with a socket prosthesis who consider a transition to bone-anchorage should be advised that their walking speed may decrease with high probability, and that their self-selected walking speed may even be slower than 3 km/h. • Restoring gait with bone-anchored versus socket prostheses and hip replacements • Osseointegrated amputees have a special gait adaptation to unload the prosthetic leg • Physiological gait is impossible • Reduced force transmission in the implant-bone interface can be ruled out as a cause • Bone-anchored prostheses can be recommended at walking speeds of slower than 3 km/h [ABSTRACT FROM AUTHOR]

Assembly Sequence Planning (ASP) is one of the well-known optimization problems in the manufacturing industry. It represents a great deal of interest over the past three decades. This paper aims to present a method for generating ASP, taking into account the stability assignment during assembly’s operations. The developed method uses the topological and geometrical assembly constraints extracted and generated from CAD system (assembly constraints, mass and center of gravity of components, interference and contact matrices), to guarantee the generation of a feasible ASP. The main contribution of this research is the development of a method which respects the stability assignment of heavy machines during the assembly’s operations. Also, it reduces the design costs and minimizes the time of replacement or repair of failing components of industrial equipments, which has become complicated task given the complexity of today’s mechanisms. A validation example is used to highlight the advantages of the proposed approach. [ABSTRACT FROM AUTHOR]

• A method to identify the 3D position of the CoG in a tiltrotor aircraft using photogrammetry and scales without previous levelling the aircraft. • Fast and automated method for the CoG measurement. • Multibody simulation of the system to obtain validation data for the proposed method. • Evaluation of the uncertainty of the measurement considering the uncertainty of the sensors used. • Suitable results of the proposed method and identification of the most relevant factor influencing the results. The aircraft weight and balance are a consequence of the own mass and the payload distribution, resulting in a position of the Centre of Gravity (CoG) that affect the behavior of the aircraft, its stability and the control effectiveness. The aircraft weight is normally measured statically using ground scales or sensors in the landing gear axles or struts, driving to 2D measurements of the CoG in longitudinal and lateral directions. Sometimes the 3D measurement is relevant because the aircraft architecture can involve weight shifts, i.e., the tiltrotor case. This paper studies the fast 3D measurement of the CoG in a tiltrotor type aircraft using photogrammetry and scales without previous levelling the aircraft. The system is modelled using multibody simulations to obtain data for the validation of the proposed methods. Finally, the expected uncertainty of the measurement is evaluated using Montecarlo method, analyzing the results statistically. [ABSTRACT FROM AUTHOR]

Balance impairment, frequent in Multiple Sclerosis patients (MS), is difficult to detect promptly with routine clinical examination. Computerized platforms can measure subtle deficit but, given the complexity of postural system, multiple tests should be adopted. To evaluate whether platform was more sensitive than Romberg Test (RT) in detecting balance abnormalities, we 1) chose a battery of posturographic tests, 2) collected normative data from 58 healthy subjects 3) applied the tests to Clinically Isolated Syndrome (n=42) and minimally impaired MS (n=76). Subjects underwent 3 trials of quiet standing with eyes open and closed (modified Clinical Test of Sensory Interaction on Balance, mCTSIB) and 4 trials of voluntary anterior and lateral maximal leaning on right and left sides (Limits of Stability, LOS), giving 10 postural indexes. For every subject, the best trials were selected for subsequent analysis. Normative values were established in a range from 1st to 99th percentile, defining balance impairment by the presence of at least 2 indexes out of range. Even adopting the above mentioned strict definition of balance impairment, the forceplate resulted more sensitive than RT, detecting abnormalities in 25% of patients, while RT was abnormal in 7% only. In RT-negative patients with 1-year follow-up (n =67) the detection of a single abnormal index was able to predict a subsequent onset of symptomatic balance impairment. The proposed procedure is quick, easy to perform and can improve the assessment of the clinical course of MS, from a pre-clinical stage up to medium degree of disability. [ABSTRACT FROM AUTHOR]

To grasp the characteristics of CO 2 emissions across provinces in China and to determine changes in the centre of gravity of CO 2 emissions over the 2000–2014 period, a gravity model is first used to examine the spatial distribution and centre of gravity of energy-related CO 2 emissions. Then, to explore the main factors driving CO 2 emission changes and to uncover feasible ways to reduce CO 2 emissions, this paper decomposes changes in energy-related CO 2 emissions into a population effect ( Δ C P ), an economic output effect ( Δ C Q ), an industrial structure effect ( Δ C S ), an energy intensity effect ( Δ C I ), an energy structure effect ( Δ C M ) and a carbon dioxide emission coefficient effect ( Δ C U ) at both the national and provincial levels based on the Log-Mean Divisia Index (LMDI) method. The results indicate that (1) energy-related CO 2 emissions rose by approximately 5.46 billion tonnes during the 2000–2014 period, with secondary industry accounting for approximately 80% of total CO 2 emissions. (2) Economic output ( Q ) was the dominant positive driving factor, and energy intensity ( I ) was the dominant negative driving factor. The population changes had a weak positive effect on CO 2 emissions, but the industrial structure effect and energy structure effect varied considerably over the years without showing clear trends. (3) Over multiple spatial scales, the contribution ratios of the factors varied significantly across provinces; in general, the positive driving effects outweighed the negative inhibiting effects. Based on these empirical findings, policy recommendations to further reduce CO 2 emissions are provided. The Chinese central and local governments should make full use of the important inhibiting factors, i.e., energy intensity and energy structure, and strive for breakthroughs in secondary sector. [ABSTRACT FROM AUTHOR]

Wheelchair stability has an impact on safety as well as wheelchair performance, propulsion and manoeuvrability. Wheelchair stability is affected by the addition of life-supporting heavy equipment, e.g. ventilators and oxygen cylinders, as well as the characteristics of the user e.g. limb amputations, obesity. The aim of the research described here was to develop and test a stability assessment system that would guide and support the adjustment of wheelchairs to individual needs, characteristics and lifestyles. The resulting system provides assessment of centre of gravity and wheelchair stability and calculates the wheelchair tipping angles. The system consists of a force platform that senses the weight distribution of the wheelchair and calculates the centres of the contact points of the wheels and the distances between them. The measurement data are transferred via a WiFi connection to a portable tablet computer where wheelchair stability parameters are calculated. A touchscreen GUI provides visualization of the stability results and navigation through the measurement modes. The developed new concept has been evaluated through technical laboratory-based testing to determine the validity of the data collected. Initial testing has been undertaken within the clinical setting in 3 large hospitals in the UK. Initial results suggest that Wheelsense® provides a valuable tool to support clinical judgement. [ABSTRACT FROM AUTHOR]

Force platform biofeedback training, whereby concurrent visual feedback of the centre of pressure (COP) is provided, has previously been used for balance training. Since the goal of balance is to maintain control of the centre of gravity (COG), specific feedback of the COG may be more likely than COP feedback to improve overall balance control. The purpose of this study was to compare the effect of concurrent visual feedback of the COP versus COG on postural control during a novel quiet standing task. Thirty-two young healthy adults (20–35 years old) were recruited. Participants were randomly assigned to receive concurrent visual feedback of either the COP or COG while standing on a foam pad. Training occurred over one session (20–30-second trials). Retention and transfer testing (i.e. without concurrent visual feedback) occurred after ∼24 h. Variability of the COG decreased, variability of COP–COG increased, and sample entropy increased with concurrent visual feedback. With practice, variability of COP, COG and COP–COG decreased whereas sample entropy increased. The decrease in variability of COP–COG was greater for those who received COG feedback than those who received COP feedback. Training effects on COP, COG and COP–COG variability were not retained after 24 h and removal of visual feedback. However, on retention and transfer testing, sample entropy was significantly higher than on baseline testing, indicating more ‘automatic’ postural control. These results suggest that concurrent visual feedback of neither the COP nor COG is superior for improving quiet standing balance control. [ABSTRACT FROM AUTHOR]

Highlights: [•] Theta burst stimulation (TBS) to right primary motor cortex (rM1) and bimanual training (BMT). [•] TBS to rM1 and BMT caused a greater shift in centre of gravity and prolonged increased spatial map. [•] TBS to rM1 and BMT individually increased map volume and spatial map. [•] Modulation of rM1 with rehabilitation may be useful in enhancing excitability in damaged cortex. [ABSTRACT FROM AUTHOR]

Highlights: [•] Navigated transcranial magnetic stimulation (nTMS) can outline cortical motor areas. [•] Novel methods were implemented for assessing muscle representation areas with nTMS. [•] Hand muscle representation can be located with high repeatability. [•] Spline interpolation method was found most suitable for estimating motor area size. [•] Spline interpolation and Voronoi tessellation can assess motor area size and location. [ABSTRACT FROM AUTHOR]

Highlights: [•] Ankle stiffness was altered passively (orthotic) and actively (muscle activation). [•] Differential effects on COP and COG sway during quiet stance were observed. [•] Implications for disorders that influence ankle stiffness via different mechanisms. [ABSTRACT FROM AUTHOR]

Abstract: Centre of gravity (CG) is one of the significant parameters of vehicle mass property related to vehicle handling. Position of CG in each direction (longitudinal, lateral and vertical) affects stability of the vehicle eventually. Change in CG position depends on different architectural arrangements of drive train and sub-systems which affect mass distribution of the vehicle. Being zero-emission technology, rapid commercialization of electric vehicle (EV) requires more emphasis on production of new automobiles and retrofitting as well. In case of retrofitting, placement of all EV drive train and other sub-systems requires both static and dynamic analysis for change in CG position due to different mass distributions. In this paper, analysis has been conducted by MATLAB SIMULINK based vehicle model to demonstrate effect of CG in vehicle maneuvering. Outcome of this investigation indicates the evaluation of different retrofitted EV architectures considering different mass distributions under the constraint of vehicle mass and dimension. This study evaluates vehicle performance with different architectures to ensure safe handling and stability in both normal and sudden maneuvering conditions of the vehicle. [Copyright &y& Elsevier]

Abstract: The aim of this study was to highlight, in sitting posture, the value of distinguishing between the movements of the vertical projection of the centre of gravity (CG v ) and its difference from the centre of pressure (CP−CG v ). A protocol for healthy, young, trained adults, consisting in tilting their trunk backward or keeping it vertical was used. A frequency analysis shows that statistically significant effects were only seen on CP−CG v movements: the RMS increased by 37% (p=0.004), while the MPF decreased by 5% (p=0.016), suggesting an increased muscular activity in these tilting postures. In contrast, no statistically significant effects on CP and CG v were reported. These data highlight the advantage, in sitting posture, of splitting overall CP displacements into basic components (i.e. CG v and CP−CG v ), each of them having a biomechanical significance. [Copyright &y& Elsevier]

Summary: This article reviews the main aspects of the interpretation of centre of pressure trajectories measured from a force platform during undisturbed upright stance control. This objective measure has been used for more than 40 years by both clinicians and fundamental scientists to assess the postural stability of both healthy and disabled individuals. Besides rough summary statistics, which provide global information on the position of the body relative to the base of support, various techniques have been proposed such as frequency analysis, fractional Brownian motion modelling, and chaos systems, to give more relevant insights from neurophysiological and biomechanical points of view. Concurrently, the contribution of the joints and muscles of the lower legs has been studied trough EMG measures as well as indices computed from data from separate measures under each foot. [Copyright &y& Elsevier]

Abstract: Background : The purpose of this study was to investigate the effects of trunk extensor muscles fatigue on undisturbed postural control in young healthy adults. Methods : Fifteen university students were asked to stand upright as immobile as possible with their eyes closed in two conditions of Fatigue and No fatigue of the trunk extensor muscles. Muscular fatigue was achieved by performing trunk repetitive extensions until maximal exhaustion. Centre of foot pressure displacements, recorded using a force platform, were used to compute the motions of the vertical projection of the centre of gravity and those of the difference between the centre of pressure and those of the difference between the centre of pressure and the vertical projection of the centre of gravity. These motions were processed through space–time and frequency domain analyses. Findings : Larger centre of pressure minus centre of gravity and centre of gravity motions in the Fatigue than No fatigue condition are observed along both the medio-lateral and antero-posterior axes, this effect being more accentuated along the antero-posterior axis. Interpretation : The present findings suggest that trunk extensor muscles fatigue deteriorates undisturbed stance control, yielding, along the antero-posterior axis mainly, (1) a greater neuromuscular requirements for ensuring standing control, as indicated by the increased centre of pressure minus centre of gravity motions, and (2) a deterioration of postural performance, as indicated by the increased centre of gravity motions. [Copyright &y& Elsevier]

Abstract: Motion of the body center of mass (CoM) can often indicate the overall effect of the strategy of forward progression used. In the present study, focus is placed on trunk movements in the sagittal, coronal, and transverse/rotation plane, as well as placement of the CoM, during gait in children with juvenile idiopathic arthritis (JIA). Seventeen children with JIA, all with polyarticular lower extremity involvement were examined before and approximately two weeks after treatment with intra-articular cortico-steroid injections. Movement was recorded with a 6-camera 3D motion analysis system in both the children with JIA and in 21 healthy controls. Trunk and center of mass movements were compared between JIA and controls, and effects of intra-articular cortico-steroid treatment were evaluated. Children with JIA were more posteriorly tilted in the trunk, contrary to the common clinical impression, and had their CoM placed more posterior and off-centred, which may have been a result of pain. With such knowledge, it might be possible to better understand the effects of their pain and involvement, and ultimately to plan a treatment strategy for improving their gait patterns. [Copyright &y& Elsevier]

Abstract: Objective. – The aim of this study was to compare the immediate effects of standard physiotherapy (S) and balneotherapy (B) on the postural capacity of subjects with lower-limb injuries. Methods. – The postural sway of 12 voluntary subjects was evaluated before (REF1 and REF2) and after two different physiotherapy sessions performed in the swimming pool (B) or under (S). The centre of pressure (CP) trajectory was recorded by use of a force platform. CP displacements in the mediolateral and anteroposterior axes were then separated into two elementary superimposed components: the horizontal motion of the centre of gravity (CG) and the difference between the CP and the vertical projection of the CG (CP-CG). The amplitude of the latter component (CP-CG) is thought to express neuromuscular activity. All trajectories were then analysed in terms of classical and frequency parameters. Results. – Postural sway did not differ before and after the physiotherapy sessions. Following both sessions, the mean CG velocity decreased significantly (P <0.5). The area of CP-CG trajectory was diminished solely by the aquatic exercise (P <0.5) and was associated with decreased amplitude of motion along the anteroposterior axis (P <0.05), which suggests decreased neuromuscular activity to maintain posture. Conclusion. – Interestingly, decreased motion was observed along the anteroposterior axis, which corresponds to ankle movements. Exercising lower-limb muscles under water could reinforce proprioceptive input, resulting in a better postural control. [Copyright &y& Elsevier]

Abstract: Postural asymmetry in humans is generally associated with different pathologies. However, its specific influence on undisturbed upright stance is poorly understood. To evaluate its separate effects on each support, the centre of pressure (CP) displacements were recorded through two force platforms. In a second step, the complex resultant centre of pressure trajectories (CPRes) were computed and decomposed into two elementary components: the horizontal displacements of the centre of gravity (CGh) and the difference in the plane of support between the vertical projection of CGh and CPRes (CP–CGv). These motions were then processed through a frequency analysis and modelled as fractional Brownian motion to gain some additional insight into their spatio-temporal organisation. Ten healthy adults were tested in three conditions consisting of various weight distributions. The quality of the mechanism involved in the control of the unloaded support CP motions appears to decrease as the asymmetry becomes more pronounced. To be precise, larger increases of the CP displacements are observed for the unloaded support compared to the loaded one. As a result, the CPRes motions are themselves augmented in the ML direction, inducing in turn larger CGh and CP–CG v motions. Postural asymmetry thus constitutes an important constraint on the control of upright undisturbed stance by generating changes in the control of both supports and by reducing the efficiency of the hip load/unload mechanisms. On the other hand, by inducing larger body sways, postural asymmetry necessitates higher energy expenditure and the setting of particular control mechanisms. [Copyright &y& Elsevier]

Abstract: The purpose of the present experiment was to investigate whether and how the head extended posture, commonly encountered in many routine activities, affects undisturbed upright stance control mechanisms in humans. Sixteen young healthy adults stood feet together, with their eyes closed and were asked to sway as little as possible in two Neutral and Extended head conditions. Centre of pressure (CP) displacements, recorded using a force platform, were used to compute the motions of the vertical projection of the centre of gravity (CGv) and those of the difference CP - CGv. A time-domain analysis shows increased mean velocity and surface covered by the trajectory of both elementary motions in the Extended head condition. A frequency analysis also reveals increased root mean squares on the CP - CGv motions, suggesting increased muscular activity in the Extended head condition. Furthermore, similar changes occur on CGv motions. Finally, modelling these trajectories as a fractional Brownian motion process demonstrates increased spatial transition point co-ordinates at which the corrective process is initiated and a more deterministic control mechanism in this corrective process involving CGv motions in the Extended head position. Together, the present findings suggest that head extension position yields a reorganisation of the control mechanisms for maintaining undisturbed upright stance. [Copyright &y& Elsevier]

Abstract: This paper presents a comparison of the performance of two different methods to realize the aggregation and the centre of gravity stages of a fuzzy controller that is under development for its integration, as an alternative power control algorithm, in the control console of the TRIGA Mark III reactor of the Mexican Nuclear Centre. In one case, an innovative method determines, in every control cycle, the group of lines that define the fuzzy aggregated set of the rule base in the continuous domain of the output variable. Likewise, the centre of gravity of this aggregated set is analytically obtained, and the corresponding controller is named exact or continuous. In the other case, a method is used to determine, in one step, both the aggregated set and its centre of gravity using the classical discretization of the universe of discourse of the output variable, thus leading to the discrete fuzzy controller. These methods were simulated in the ascent and regulation of neutron power in a TRIGA Mark III reactor. The performance parameters used for the comparison between the two methods were: The required number of floating point operations, the time required to attain a certain power level, the neutron power time response, and the reactor period values. [Copyright &y& Elsevier]

Aim. – To assess the effects of utmost fatigue on balance control in upright quiet stance.Method. – Eleven subjects performed a postural task before and after completing a long distance triathlon. The centre of pressure (CP) displacements was recorded through a force platform and decomposed from a biomechanical relationship into two elementary motions: the horizontal motions of the centre of gravity (CG), and the difference CP – CG. These motions were then studied through three different analysis processes.Results. – A large increase of the oscillations is seen for both elementary motions. Interestingly, CG motions are particularly sensitive to fatigue and present an 83% increase for mean amplitudes while only a 44% increase is seen for CP – CG motions. Moreover, a large increase is observed in the mean time interval and the mean distance covered before a corrective process occurs. Finally, impairment of the muscular means brought into play and the decrease in ability to minimise body sways following utmost fatigue are discussed.Conclusion. – Postural instability following exhausting exercise is due both to muscular activity perturbation and to an impairment of the system’s capacity to control the position of the CG. This last point seems of a particular interest since it highlights a possible limit of the system to handle the controlled. [Copyright &y& Elsevier]

Objective. To assess the effects of visual feedback gain, which express the amplitudes of the displacements of the centre of pressure displayed on a computer screen.Design. The controlling variable, the centre of pressure trajectories, recorded using a force platform, were decomposed into two elementary motions: (1) the horizontal displacements of the centre of gravity and (2) the vertical projection of the difference between centre of pressure and the centre of gravity. These motions were processed through frequency analysis and modelled as fractional Brownian motion to assess their spatio-temporal linkage and their degree of control.Background. Although tests to modify the feedback gain have already been carried out, the specific effects from a biomechanical and motor control point of view need to be assessed.Methods. Thirteen healthy adults were tested through various visual feedback gains performed in random order.Results. By increasing the visual feedback gain, no difference is observed between centre of pressure and centre of gravity motions whereas a progressive diminution of centre of gravity horizontal motions is seen. This latter effect is principally explained by a reinforcement of control during corrective processes.Conclusions. When the control of centre of gravity constitutes the main flaw in undisturbed stance maintenance, the efficiency of a visual feedback rehabilitation protocol should be largely improved by using an enhanced gain.vsp sp="1">RelevanceIn-depth knowledge of the effects originating from modifications of the visual feedback gain should allow to optimise the use of this technique as a rehabilitation tool. [Copyright &y& Elsevier]

Body sway was studied in standing with eyes closed during quiet breathing and apnoea. The hypothesis was that absence of ventilation improved balance. Performance and control of balance were assessed by centre of gravity and centre of pressure motions respectively. Eight healthy male subjects participated in the study. The analysis was performed for the first 20s when no activity of the diaphragm and no force variation at thoracic and abdominal levels were observed in apnoea condition. Performance and control were significantly improved in apnoea from 17 to 26% for the planar parameters; this improvement was only observed along the medio-lateral axis (around 34%), probably due to upper body asymmetry and diminution of the number of degrees of freedom that can be mobilised along this axis. In conclusion, ventilation in quiet breathing is a perturbing factor in human standing. [Copyright &y& Elsevier]

An investigation of the interaction between local fatigue and vision on postural control and postural stability was carried out. Fatigue was effected in a sitting position and was assumed based on a shortening of the exertion time of the soleus muscles (60% of their maximal voluntary contractions). Postural stability was assessed by centre of gravity motion, which was computed from centre of pressure motion, evaluating postural control. Ten healthy male subjects were asked to stand as still as possible with eyes open (EO) and eyes closed (EC) before and after the fatigue protocol. Results showed that fatigue produced similar effects for the two vision conditions on postural control and postural stability analyzed separately, increasing postural control and leaving postural stability unchanged. Local fatigue essentially produced an increase of neuromuscular activity in high frequencies. However, this increase was more pronounced for the EO, as compared to the EC condition. [Copyright &y& Elsevier]

Objectives. To assess various ankle orthoses presenting different physical characteristics.Design. The postural performance in bi-pedal stance of 14 healthy adults was assessed during four different ankle orthoses conditions.Background. Resultant ankle stiffness is an important component in undisturbed upright postural regulation.Methods. The centre of pressure displacements issued from the force platform were used to compute the horizontal motions of the centre of gravity, the controlled variable, and those of the difference between the centre of pressure and the vertical projection of the centre of gravity from which ankle stiffness can be estimated. Their respective contribution was assessed through a frequency analysis and a fractional Brownian motion modelling to determine their spatio-temporal linkage and their degree of control.Results. Ligacast, the more rigid model, induces the larger decrease, principally in the medio-lateral direction, in both centre of pressure minus centre of gravity and centre of gravity amplitudes. Dynastab reduces only the centre of pressure minus centre of gravity motions in both medio-lateral and antero-posterior directions. Lastly, no specific effect was observed for the less rigid Ligaflex for each motion and each direction. These effects are mainly explained by a reduction in the distance covered until the corrective process is initiated, the corresponding time interval being unchanged. In addition, depending on the model, the corrective processes appear more or less controlled.Conclusions. Modulating the ankle joint stiffness by using various models of orthoses induces some contrasted behaviours, hence suggesting that postural control does not result solely from resultant ankle stiffness.vsp sp="1">RelevanceThis data, contributing to the understanding of orthotic devices by emphasising their benefits, allows the practitioners and physical therapists to take into account the specific effects generated by each model. [Copyright &y& Elsevier]

The visual feedback technique (VFB) is recognized by several studies as a valuable tool for re-establishing the balance functions. However, one former study has highlighted the fact that the increased control induced by this technique infer both favourable (the amplitudes of the horizontal motions of the centre of gravity (CoGh) are diminished) and unfavourable features (the vertical difference between the CoGh motions and centre of pressure (CoP) trajectories are enhanced). One means to decrease these CoP–CoGv motions is to delay their display on the screen of the monitor. To assess these behavioural effects, 16 healthy adults were evaluated with various delays from 0 to 1200 ms. CoP displacements, measured through a force platform, were decomposed into two elementary motions: CoGh and the difference CoP–CoGv. A fractional Brownian motion modelling of these motions allowed to determine from which distance and for how long the corrective process takes over and to what extent the motion is controlled. Compared to the VFB real time condition, increasing the delay induces some effects mainly on the CoP–CoGv motions which are largely diminished, the most striking effect appearing for delays exceeding 600 ms. Despite the lower forces these reduced amplitudes infer to control body sways, the amplitudes of the CoGh motions tend to increase slightly. Considered as a whole, whilst retaining the beneficial aspects of VFB without delay and significantly suppressing the unfavourable features, the data suggests that the method of delaying the screen display optimises the VFB technique. [Copyright &y& Elsevier]

Upright undisturbed stance constitutes a fundamental attitude involving very cunning sensori-motor strategies. Until now, few analyses on postural control have been undertaken to explain the influence of both supports in this particular task. With the aim of analysing asymmetrical postures resulting from neurological (hemiplegia) or traumatic (amputation) origins, a new analysis and a reference framework are proposed, describing the influence of each support in upright stance maintenance. Ten healthy adults (eight men and two women ranging in age from 20 to 42 years) volunteered for this study. The subjects were required to remain as still as possible in upright stance. The control mechanisms for equilibrium maintenance were estimated by separate measures of the elementary and resultant centres of pressure through two force platforms. The analysis of the relationship between the elementary and resultant centres of pressure on the one hand and the centre of gravity on the other hand emphasises that both took place similarly and at the same time in the control of upright undisturbed stance. This control is done through two strategies that come into play at the level of the ankle and/or hip in the medio-lateral and antero-posterior directions, respectively. Furthermore, the various trajectories (elementary and resultant centres of pressure, centre of gravity) and analytical methods (frequential, correlations and cross-correlations) are compared. This methodology should be very interesting in the analysis of pathologies inferring postural asymmetry in weight distribution, since one could suppose that asymetric patients could be characterised by specific control of both supports. [Copyright &y& Elsevier]

To assess the possible interactions between the physiological mechanisms involved in eyelid closure and stance maintenance, 20 healthy adults were required to keep their eyes open in the dark (EOd), in daylight (EO), or to close them normally (EC), respectively and in random order. The analysis was focused on elementary motions computed from the complex centre of pressure (CP) trajectories, that is to say the vertical projection of the centre of gravity (CGv) and the difference between CP and CGv (CP−CGv). The results indicate that the mean amplitudes of the CP−CGv spectra are statistically reduced in EOd when compared to the EC condition. This diminution is thought to express a decrease in the level of activity of lower limb muscles involved in stance control. Interestingly, the CNS does not really seem to gain from these reduced horizontal accelerations at the CG level since the CGv amplitudes are in turn only slightly reduced. It can thus be hypothesised that, despite the fact that visual information in the EOd condition remains unavailable, the somesthetic cues continue to play a minor role in the detection–correction process aimed at controlling undisturbed stance. [Copyright &y& Elsevier]

Objective. To evaluate the instantaneous effects of visual feedback on undisturbed stance control mechanisms.Design. The controlling variable, the centre of pressure trajectories, recorded using a force platform, were decomposed into two elementary motions: (1) the horizontal displacements of the centre of gravity and (2) the vertical projection of the difference between centre of pressure and the centre of gravity. These motions were processed through frequential analysis and modelled as fractional Brownian motion.Background. Even though visual feedback protocols are advantageously used for rehabilitation purposes, their immediate effects from biomechanical and motor control points of view need to be assessed.Methods. Twelve healthy adult subjects were tested through eyes open and visual feedback conditions.Results. A significant amplitude increase in the difference between the centre of pressure and the centre of gravity motions and a decrease in the centre of gravity motions are observed during visual feedback. The fractional Brownian motion modelling analysis reveals an enhanced control of these elementary motions. The point at which the corrective process is initiated is increased with visual feedback whereas the time delay remains the same.Conclusions. The decrease of the centre of pressure displacements classically observed through visual feedback protocol initially results in a reduction of the centre of gravity motions and an augmentation of the difference between centre of pressure and centre of gravity motions, hence suggesting increased muscular activity.RelevancePrecise knowledge of the effects generated by such feedback protocol should allow to optimise it as a rehabilitation tool. [Copyright &y& Elsevier]

Postural stability and postural control were studied before and after a fatigue protocol of soleus muscles. Postural stability was assessed by the centre of gravity motion, which was computed from the motion of the centre of pressure, evaluating the postural control. Ten healthy male subjects were asked to stand as still as possible with eyes open before and after the fatigue protocol, performed in a sitting position. Fatigue was assumed on the basis of a shortening of the exertion time of the soleus muscles at 60% of their maximal voluntary contraction. Results of the whole group showed that fatigue modified postural control but did not change postural stability. The same results were observed only for some subjects. However, these results indicate an increase of the neuromuscular activity in high frequencies. [Copyright &y& Elsevier]

In many applications the location of the centre of gravity of a mechanical part is an important factor that a designer must consider. If it is not in a desired location, a part might not work properly, e.g. unbalanced force might be generated in a rotational part. After a part is modeled, its centre of gravity cannot be altered unless its external shape or internal mass distribution is changed. However, the external shape is usually constrained by other design considerations. In this paper, an algorithm is proposed for controlling the centre of gravity of a hollowed part. Using this algorithm, the location of the centre of gravity of a part is controlled by changing its internal mass distribution. [Copyright &y& Elsevier]

Body centre of gravity (CG) mechanics and electromyographic activity of flexor–extensor antagonistic muscles of the lower limb were simultaneously recorded in lowest and middle-level gait disorders. Muscle co-contractions between tibialis anterior and triceps surae, and between rectus femoris and hamstrings were evaluated. CG mechanics was assessed by the external mechanical work (Wext) done to translate the CG with respect to the ground, and the recovery quantifying the efficacy of gait mechanism by the amount of energy transferred between gravitational potential and kinetic energies of the CG. The results showed a strong relationship between CG mechanics and the co-contractions of the main flexor–extensor ankle muscles. In middle-level gait disorders, our results suggest that the ankle antagonistic muscle co-contractions and the CG mechanics could provide information about gait mechanism and the integrity level of the locomotor program. [Copyright &y& Elsevier]

OBJECTIVE: To evaluate, in normal and healthy adults, the postural effects induced by a protocol of body sway mirror feedback.MATERIALS AND METHODS: Two experimental conditions, one consisting in staring eyes open (EO) and one consisting in mirror feedback (MFB), are randomly proposed. Displacements of the centre of pressure (CP), issued from a force platform, are advantageously decomposed along medio-lateral ML and antero-posterior AP directions into two elementary components: the horizontal motions of the centre of gravity (CGh) and the difference CP-CGv. The former is recognised as the main controlled variable in upright stance whilst several clues can be assessed by the latter: the overall muscular activity, the ankle stiffness and the horizontal accelerations communicated to the CG. Elementary motions CGh and CP-CGv are then processed in the frequential domain and characterized through RMS and MPF parameters.RESULTS: For CP-CGv motions the MFB protocol induces larger MPF along the AP direction and thus an increased ankle stiffness. In addition, the RMS are slightly decreased, indicating that less motor units are called into play. On the other hand, no real effect is observed in the ML direction. A general trend is that the CGh amplitudes are diminished by the MFB protocol, especially in the ML direction where a statistical effect is noticed.CONCLUSION: The specificity of the effects induced by the MFB technique makes it an appropriate tool for re-establishing, especially on the AP direction, the balance functions, in particular those involving exaggerated CP-CGv motions. [Copyright &y& Elsevier]