Characteristics of the maintenance of the vertical posture during standing with an asymmetrical load on the legs

Motion of the common center of pressure (CCP) and center of pressure (CP) of each leg was studied in subject standing by each leg on separate force platform. Subject maintained the vertical posture during ordinary standing and during standing with visual feedback from the CCP position presented on the monitor. In both conditions the body weight was either symmetrically distributed between legs or partially transferred to right or to left leg. During standing with symmetrical loading of both legs the visual feedback led to the decrease the standard deviation of CCP and CP of each leg. After the transfer of the body weight on one leg standard deviation of the CCP and CP of each leg was not changed when the visual feedback was present. It is likely that the afferentation from loaded leg was sufficient for define the equilibrium body position. The velocity of motion of CCP increased with presence of the visual feedback during standing with all variants of weight distribution. The velocity of motion of CP of left leg increased with visual feedback during standing with symmetrical load and with load of the right leg. The velocity of motion of CP of right leg increased with visual feedback during standing load of the left leg. One could suggest that the tracking of the CCP position was mainly occurred by the leg that less involved into postural control. During standing with symmetrical weight distribution the afferentation from dominant leg more significant for the elaboration of referent body position for maintaining of vertical posture and the tracking CCP position influenced greater on the motion of the CP of the nondominant left leg. During standing with asymmetrical weight distribution the loaded leg is more involved into postural control and the tracking CCP position occurred by unloaded leg. It is suggested that the elaboration of referent body position for maintaining of vertical posture require the stationary position for leg that was mainly involved into postural control.

Maintenance of a vertical posture was studied in standing subjects with a fixed knee joint of one leg and a different weight distribution between the legs. Knee fixation on one leg did not affect the speed of movements of the common center of pressure (CP) at any weight distribution between the legs, and the stability of vertical posture was therefore unchanged. However, the relative contributions of the legs to the posture control changed when knee movements of one leg were restricted. The speed of CP movements of the free leg was independent of the weight loading on the leg. The speed of CP movements of the leg with the knee fixed depended on the weight distribution and was higher when the leg was loaded. Thus, the leg with the fixed knee joint made a greater contribution to maintaining vertical posture when the leg was loaded. Yet its contribution was comparable with that of the unloaded free contralateral leg even in this case, as was evident from lack of differences in CP movements between the two legs. It was assumed that the leg with the free knee joint played a major role in maintaining equilibrium of vertical posture, while the leg with the fixed knee joint mostly acted to more finely adjust the body position.

Body sway has usually been studied during symmetrical standing while lower limbs equally contributed in upright posture. The present study aimed to examine the dynamics of body sway while turning during standing with symmetrical and asymmetrical weight distribution between the legs. Subjects performed a body turn of 30° to the right and left during quiet standing and standing with the right or left foot loaded with 70% of body weight. We found that body turn in the symmetrical posture induced weight increase on the foot contralateral to the turning direction and the common center of pressure (COP) velocity increase. Body turn in the asymmetrical posture induced further loading of the foot that was initially overloaded; also turning in the direction of the unloaded foot affects weight distribution more than turning in the direction of the overloaded foot. The posture transition from symmetrical to asymmetrical induced the common COP velocity increase and forward protraction of the unloaded foot COP. Turning in the asymmetrical posture produced further increase of the common COP velocity and further forward protraction of the unloaded foot COP. Moreover, when the left leg was unloaded this resulted not only in left leg's COP forward, but also in left leg's COP lateral protraction, and left leg's COP frontal velocity increase. These findings reveal that body position and weight distribution between the feet interact to stabilize upright posture and show the effect of footedness during turning in asymmetrical standing.

We studied the vertical posture in subjects in the standing position with different turns of the body and different distributions of the load between the legs. We recorded the motion of the projection of the common center of pressure (CCP) and of the center of pressure (CP) for the left and right legs. The predominant direction of CP movement was determined from a stabilogram, and then changes of this direction were analyzed during body turns and with different load distributions between the legs. Body turn led to the shift of the predominant direction of CCP movement towards the turn side. This change in the direction of CCP movement was observed with any load distribution between the legs. At the same time, weight transfer to one leg also led to the direction shift of CCP movement towards the loaded leg. The direction of CP movement of the loaded leg did not change, but the direction of CP movement of the unloaded leg shifted clockwise upon unloading both right and left legs. We assume that the changes in the mechanisms of maintaining the vertical position with asymmetric distribution of the leg load may be associated not only with the change in the force interaction with the supporting surface, but also with asymmetry of axial muscle tone.

Introduction The etiology of spinal deformity in idiopathic scoliosis is unclear to date. One of the suspected influences is the asymmetric loading condition involved in the disorder. The aim of this project is to test the hypothesis that asymmetric dynamic loading influences the morphological and biological characteristics of the intervertebral discs in scoliosis. The study is performed with organ cultured discs by using a custom-designed asymmetrical loading device. Material and Methods Bovine caudal discs (6–10 months) were used in current study. For symmetric dynamic loading (Parallel), discs were placed in custom-designed chambers, and compressed by parallel metal plates in a Bose mechanical testing device. For asymmetric dynamic loading (Wedge), a 10° wedge was placed underneath the discs to mimic the load bearing condition of discs in scoliotic patients. The discs were submitted to 2 different load regimes: (1) 1 hour dynamic loading (0.02–0.4 MPa, 1Hz) and 23 hours free swelling culture for 7 days; (2) 1 hour dynamic loading (0.02–0.4 MPa, 1Hz) and 23 hours static loading (0.2 MPa) for 7 days. Disc heights were measured with caliper before and after each loading. After 7 days of culture, gene expression levels of aggrecan (ACAN), type I and II collagen (COL1 and COL2), IL1, IL6, and MMP1 in the annulus fibrosus was analyzed by real-time PCR. Genes that have been found dysregulated in human scoliotic discs compared with healthy controls were also measured in the organ cultured discs, including MMP13, type X collagen (COL10), CXCR4, BMP3, S100A12, and S100A8 ( n = 8). Results Disc height showed a constant drop in load regime 2, while a temporary decrease after 1h dynamic loading followed by free swelling recovery was noted in load regime 1. After 7th dynamic loading, the change in shape was greater in load regime 2 (disc height ratio wedged to non-wedged side of 0.81), than that in load regime 1 (height ratio of 0.87, p < 0.05). Under load regime 2, MMP13 gene expression level increased 6.1-fold in Wedge disc compared with Parallel disc, while gene expression levels of COL10, CXCR4, BMP3, S100A12, and S100A8 were not affected. Gene expression levels of ACAN, COL1 and COL2 under load regime 1 were significantly higher compared with load regime 2. Moreover, discs under load regime 2 showed a trend in higher IL1, IL6, and MMP1 gene expression compared with regime 1. Conclusion Diurnal dynamic loading and free swelling recovery could maintain the gene expression of organ cultured discs at their physiological level. Diurnal dynamic loading followed by static loading mimicked a degenerative condition, as indicated by lower anabolic and higher catabolic gene expression. These results suggest that recovery of disc height and morphology after dynamic load may help to prevent degeneration of discs under constant loading. Asymmetric dynamic and static loading regime induces an increase in MMP13 gene expression compared with symmetric loading, which was also observed in a human scoliosis sample dataset. These results indicate that short-term asymmetric loading may be used to mimic early changes associated with the onset of scoliosis. Acknowledgment This study is supported by AOSpine International.

PurposeTo determine the effects of asymmetric loads on muscle activity with the bench press.MethodSeventeen resistance-trained men performed one familiarization session including testing one repetition maximum (1RM) and three 5 repetition maximum (RM) lifts; using symmetric loads, 5% asymmetric loads, and 10% asymmetric loads. The asymmetric loading (i.e., reduced load on one side) was calculated as 5% and 10% of the subject`s 1RM load. In the experimental session, the three conditions of 5RM were conducted with electromyographic activity from the pectoralis major, triceps brachii, biceps brachii, anterior deltoid, posterior deltoid, and external oblique on both sides of the body.ResultsOn the loaded side, asymmetric loads reduced triceps brachii activation compared to symmetric loads, whereas the other muscles demonstrated similar muscle activity between the three conditions. On the de-loaded side, 10% asymmetry in loading resulted in lower pectoralis major, anterior deltoid, and biceps brachii activation compared to 5% asymmetric and symmetric loading. On the de-loaded side, only pectoralis major demonstrated lower muscle activation than symmetric loads. Furthermore, asymmetric loads increased external oblique activation on both sides compared to symmetric loads.ConclusionsAsymmetric bench press loads reduced chest and shoulder muscle activity on the de-loaded side while maintaining the muscle activity for the loaded side. The authors recommend resistance-trained participants struggling with strength imbalances between sides, or activities require asymmetric force generation (i.e., alpine skiing or martial arts), to implement asymmetric training as a supplement to the traditional resistance training.

The influence of the age factor on the contribution of the vestibular, visual, and proprioceptive sensory systems to the function of spatial orientation was assessed using the stabilometry method (ST-150, Mera, Moscow, Russia) during the vertical stance of a healthy person (N = 69, from 20 to 83 years old, of which 42 women and 27 men). Three age groups of subjects were examined: I (young, 20–25 years old, n = 37), II (middle-aged, 44–64 years old, n = 17 people), and III (elderly and old, 65–83 years old, n = 15). The subjects performed the Romberg test (stand with closed eyes) and postural stability (standing on a hard and soft surface) and a combined test (Romberg test + postural stability). This made it possible to compare the stabilometric parameters (the length and speed of the trajectory and the area of movement of the common center of pressure (COP)) under four conditions: 1) standing with eyes open on a stable surface (SS – EO), 2) eyes closed on a stable surface (SS – EC), 3) standing with eyes open on a thick layer of unstable surface (foam) (US – EO), and 4) eyes closed on a thick layer of unstable surface (foam) (US – EC). To calculate the contribution of sensory systems to the function of maintaining balance in a vertical stance, a formula was used. An increase in the length of the COP trajectory with increasing age was revealed. At the same time, only an insignificant change in the relative contribution of sensory systems to the parameters of the stabilogram was noted in middle-aged and older people compared to young people.

Objective. To assess biomechanical measures of static dynamic stability of the body of rhythmic gymnastics female athletes in the basic balances at the stage of specialized basic training. Methods. Theoretical analysis and generalization of scientific literature, methodological and practical experience of the trainers; method of expert assessments using video analysis of the technique of performing basic balances; stabiloanalyzer "Stabilan 01-2" to record the movements of the common center of pressure (COP) of the feet on the support, i.e. the coordinates at different time points that reflect the features of static dynamic stability. Three basic balance tests were performed. The study involved young female gymnasts of the Republican Complex Children and Youth Sports School "Avangard" (Kуiv) aged 10-14 years (n = 30), of which 20 athletes have the rank of Candidate for Master of Sport and 10 gymnasts have the rank of First-Class Sportsman. Results. It has been found that, at the stage of specialized basic training, female athletes in rhythmic gymnastics, along with a stable demonstration of competitive compositions, have technical errors that are associated with an insufficient level of development of sensorimotor coordination, orientation in space and time, and static dynamic stability of the body. Indicators of biomechanical analysis of stabilograms, which were recorded during the performance of the basic balances by the subjects, show that stability control is achieved both through macro and micro-oscillations of the body, as well as the controlled ratio of the trajectory lengths of the common center of pressure on the support along the frontal and sagittal line. In some gymnasts, when performing basic tests, displacements along frontal and sagittal lines approached the ratio of 1:1 that indicates the effective formation of a system of symmetric motor actions for the control of static dynamic stability. Conclusion. On the basis of individual measures of static dynamical stability of the body of rhythmic gymnastics female athletes at the stage of specialized basic training, an instructional program of exercises should be developed that will be aimed at development and improvement of static dynamic stability of the body using the technology of biological feedback in the system gymnast–stabilograph. Key words: rhythmic gymnastic, basic training, balances, body stability, technique, stabilography, competitive compositions.

The vertical posture was studied during standing with fееt on the support surfaces of different structures. The movements of the center of pressure (CP) of each leg and the common CP (CCP) were recorded while the subject stood with a support on a smooth floor and with the support of one foot on a spike mat (SM) with different load distributions between the legs. When the body weight was transferred to one leg during standing under ordinary conditions on a smooth floor, the CP of the loaded leg moved more than the CP of the unloaded leg; i.e., the posture sway was compensated mainly due to the activity of the loaded leg, which created a larger torque. When the subject stood with one foot on the SM, the CP movement of this leg did not depend on the leg load and was about 60% of the CP movement of the leg on the smooth floor. Apparently, the CP displacement of the unloaded leg on smooth support was larger than the CP displacement of the loaded leg creating the torque necessary for compensating the body sway. Thus, maintaining the vertical posture was carried out mainly by the leg standing on the smooth support. It is assumed that additional stimulation of different surface and deep receptors of the foot caused by foot support on the SM hampered the perception of its CP position, and the vertical posture was maintained mainly by the leg afferent signals from which more precisely reflected the CP position.

Three-dimensional panels are one of the modern construction systems which can be placed in the category of industrial buildings. There have always been a lot of studies and efforts to identify the behavior of these panels and improve their capacity due to their earthquake resistance and high speed of performance. This study will provide a comparative evaluation of behavior of updated three-dimensional panel\'s structural components under lateral load in both independent and dependent modes. In fact, this study tries to simultaneously evaluate strengthening effect of three-dimensional panels and the effects of system state (independent, L-shaped and BOX shaped Walls) with reinforcement armatures with different angles on the three-dimensional panels. Overall, six independent wall model, L-shaped, roofed L-shaped, BOX-shaped walls with symmetric loading, BOX -shaped wall with asymmetrical loading and roofed BOX-shaped wall were built. Then the models are strengthened without strengthened reinforcement and with strengthened reinforcements with an angle of 30, 45 and 60 degrees. The applied lateral loading, is exerted by changing the location on the end wall. In BOX-shaped wall, in symmetric and asymmetric loading, the load bearing capacity will be increased about 200 and 50% respectively. Now, if strengthened, the load bearing capacity in symmetric and asymmetric loading will be increased 3.5 and 2 times respectively. The effective angle of placement of strengthened reinforcement in the independent wall is 45 and 60 degrees. But in BOX-shaped and L-shaped walls, the use of strengthened reinforcement 45 degrees is recommended.

Abstract: This research describes the evolution of the spatial effects of foundation pits considering internal support and external loads. Based on the existing concept of “plane strain ratio”, the term “plane strain ratio considering maximum surface settlement” is proposed to characterize the spatial effects of an asymmetric foundation pit. A series of finite element model calculations were carried out using the Nanchang Aixi Lake foundation pit, including 1) the calculation of simulated actual conditions, 2) the calculation of simulated full symmetric load, and 3) the calculation of simulated asymmetric load. The results indicate that for the symmetric condition at 20 kPa and below, the spatial effect range increases as the load increases. For the symmetric condition above 20 kPa, the load has a negligible impact on the spatial effect range. On the side with a larger load under asymmetric loading conditions, the spatial effect of the working condition below 30 kPa is smaller than the corresponding symmetric load. On the side with a smaller load, the spatial effect of the working condition above 80 kPa increases compared with that of the corresponding symmetrical load. Given and verified are the modified fitting equations that take into account the influence range of spatial effect on both sides of the foundation pit under symmetrical and asymmetrical loads.

Objectives: The objective of the study was to determine the optimal use of a new optical device, the RibEye system, intended to obtain internal ribcage deflections from tests using anthropomorphic test dummies. Specifically, the study was designed to determine the most efficacious mounting location of light emitting diodes (LEDs) on the ribs and sternum in the 50th percentile male Hybrid III dummy. Methods: Optical signal drop-out and accuracy assessment tests were conducted. In the former series, symmetric antero-posterior chest compressive loading was accomplished using cylindrical and square indenters, and asymmetrical compressive loading was accomplished using unilateral offset and diagonal belt-type loadings. LEDs were mounted to multiple ribs bilaterally at varying locations on the ribcage. The internal chest potentiometer available in the Hybrid III dummy was used. The latter series, aimed at examining the system accuracy, consisted of tests with LEDs mounted to the 4 corners of the sternum, termed sternum-mounted LED tests; rib-mounted tests wherein LEDs were mounted either to a specific rib or in the intercostal space of two successive ribs; rib-mounted tests with rotated chest simulating oblique loading; and indenter-mounted isolated LED tests. An electro-hydraulic testing device was used to apply compressive loads via an indenter in all tests. Displacement profiles were extracted from the optical system records, drop-out evaluations were conducted, and the system accuracy was evaluated by comparing data from the indenter and/or internal chest potentiometer. Results: In general, results indicated that the RibEye system captures rib cage deformations effectively. Under symmetric loading, LEDs on the sternum responded similar to the internal chest potentiometer. The accuracy of the system depended on the location of position of the LEDs on the rib, magnitude of rib deformation, and potential interference from internal dummy structures such as the presence of the internal chest potentiometer. Optimum locations for LED placement were found to be at a distance of 9 cm, measured along the outer curvilinear path of the rib from the mid-sternum on either side. At this location, the system showed no signal drop-out at deflections representative of the United States current frontal impact Injury Assessment Reference Values. Signal drop-out was also depended on the type of loading: diagonal belt-type loading produced more signal loss. Mounting LEDs away from the center of the rib representing eccentric superior-inferior (z) axis placement also resulted in loss of accuracy. Conclusions: These controlled evaluations provide a fundamental understanding of the performance of the system as installed in the 50th percentile male Hybrid III dummy and its ability to measure both antero-posterior and lateral components of deflections at multiple ribs, including the sternum for frontal impact applications. The system may be optimally used to gather rib deflection data without signal drop-out under symmetrical and asymmetrical loadings when LEDs are mounted on the superior-inferior centerline of the ribs with no eccentricity along the z-axis and at the 9-cm location from the mid-sternum on either side of the ribcage and at any corner on the sternum to obtain sternum deflections.

The school backpack constitutes a daily load for schoolchildren: we set out to analyse the postural effects of this load, considering trunk rotation, shoulder asymmetry, thoracic kyphosis, lumbar lordosis, and sagittal and frontal decompensation from the plumbline. A group of 43 subjects (mean age = 12.5 ± 0.5 years) were considered: average backpack loads and average time spent getting to/from home/school (7 min) had been determined in a previous study conducted on this population. Children were evaluated by means of an optoelectronic device in different conditions corresponding to their usual everyday school backpack activities: without load; bearing 12 (week maximum) and 8 (week average) kg symmetrical loads; bearing an 8 kg asymmetrical load; after fatigue due to backpack carrying (a 7-minute treadmill walking session bearing an 8 kg symmetrical load). Both types of load induce changes in posture: the symmetrical one in the sagittal plane, without statistical significant differences between 8 and 12 kg, and the asymmetrical one in all anatomical planes. Usual fatigue accentuates sagittal effects, but recovery of all parameters (except lumbar lordosis) follows removal of the load. The backpack load effect on schoolchildren posture should be more carefully evaluated in the future, even if we must bear in mind that laws protect workers to carry heavy loads but not children, and results in the literature support the hypothesis that back pain in youngsters is correlated with back pain in adulthood

The shift of center of pressure (CP) of body and CP of each leg was studied during Achilles tendon vibration of one or both legs while subject was standing with symmetrical load on the legs or with the load transferred on one leg. The CP shift of standing subject during unilateral Achilles tendon vibration depended both on the side of the tendon vibration and on the leg load. When standing with a load transferred on one leg the shift of common CP was larger than when the vibration was applied to the loaded leg. The CP shift of one leg was greater if the vibration, and the load was applied to it. Vibration of unloaded leg caused a CP shift in the contralateral loaded leg. In this case, the vibration of left unloaded leg caused no noticeable CP shift of left leg, while the vibration of the unloaded right leg caused CP shift of right foot. In the same conditions of load and vibration the CP displacement of right leg was larger than the CP shift of left foot. It can be assumed that the change in the load on the leg and unilateral vibration of leg muscles change of the internal representation of the vertical body axis, which affects the CP position of one leg during the muscles vibration.

Interlimb asymmetries may influence contralateral knee osteoarthritis (OA) progression, yet research remains unclear. This study examined whether patient-reported outcomes and knee biomechanics differ between individuals with knee OA exhibiting symmetrical versus asymmetrical knee loading. Forty-three individuals with knee OA were dichotomized into symmetrical (≤14% asymmetry; n = 19) and asymmetrical (>14% asymmetry; n = 24) groups based on total joint moment symmetry indices. Participants completed the Knee Injury and Osteoarthritis Outcome Score and Intermittent and Constant Osteoarthritis Pain questionnaires. Three-dimensional kinematics and kinetics were collected during walking at a self-selected speed. Independent t tests and statistical parametric mapping examined between-group differences in patient-reported outcomes and biomechanical measures. Individuals with symmetrical knee loading had worse Knee Injury and Osteoarthritis Outcome Score activities of daily living scores (P = .041) than those with asymmetrical loading. Individuals with symmetrical knee loading exhibited less knee extension moment during late stance (P = .031) and lower knee adduction moment range in their affected knee compared with asymmetrical loaders. Individuals with symmetrical knee loading walked with lower knee flexion angles (P = .011), less midstance unloading (P = .011), and lower peak knee flexion moment (P < .001) in their contralateral knee compared with asymmetrical loaders. Symmetrical knee loading was associated with affected and contralateral knee biomechanics that were consistent with more severe knee OA and worse functional outcomes.