Carrying Asymmetric Loads While Walking on a Treadmill Interferes with Lower Limb Coordination

O71: Skeletal and anthropometric determinants of gait balance in asymptomatic adult subjects

Carrying asymmetric loads during stair negotiation

P36: Relation between navicular mobility and multi-segment foot kinematics during walking

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.

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.

In practical engineering, natural soil deposits often sustain an initial driving force prior to cyclic shear, owing to earthquakes, traffic and waves; such asymmetrical loading conditions may significantly affect the liquefaction susceptibility and failure mechanism of sand. To understand the typical cyclic liquefaction responses, comprehensive asymmetrical cyclic loading tests were conducted on sand samples subjected to either compressional or extensional static stress. The results indicated that different stress conditions can result in three distinct failure mechanisms: flow liquefaction, cyclic mobility and residual deformation accumulation. According to the experimental observations, an anisotropic sand model was developed within the framework of the anisotropic critical state theory. The model employed a fabric-dependent dilatancy, and accounted for the effects of the fabric evolution and accumulated loading index on the plastic hardening, in order to better reflect the cyclic degradation of the plastic modulus. The predictive capacity of the model was confirmed through undrained monotonic test results for samples with different densities. Comparisons between the model responses and experimental results indicated the excellent capabilities of the developed model in terms of capturing the typical deformation, strength and fabric characteristics of different cyclic failure mechanisms of sand under either symmetrical or asymmetrical loading conditions.

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.

Forces acting on the stator teeth of the 400 kVA, 4 pole synchronous generator were analyzed for asymmetric electric load conditions. Measurement of the flux density was performed with the measuring coils installed on the stator teeth and calculations were done by finite element method. Measured data was processed to determine stator teeth radial forces through Maxwell stress tensor integration algorithm. Processed data was used for detection of asymmetric load condition. Parameters of the measuring coil sensors and their adequate position can be determined with finite element calculation before performing sensor installation on the machine.

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.

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.

Lower limb ankle exoskeletons have been used to improve walking efficiency and assist the elderly and patients with motor dysfunction in daily activities or rehabilitation training, while the assistance patterns may influence the wearer's lower limb muscle activities and coordination patterns. In this paper, we aim to evaluate the effects of different ankle exoskeleton assistance patterns on wearer's lower limb muscle activities and coordination patterns. A tethered ankle exoskeleton with nine assistance patterns that combined with differenet actuation timing values and torque magnitude levels was used to assist human walking. Lower limb muscle surface electromyography signals were collected from 7 participants walking on a treadmill at a speed of 1.25 m/s. Results showed that the soleus muscle activities were significantly reduced during assisted walking. In one assistance pattern with peak time in 49% of stride and peak torque at 0.7 N·m/kg, the soleus muscle activity was decreased by (38.5 ± 10.8)%. Compared with actuation timing, the assistance torque magnitude had a more significant influence on soleus muscle activity. In all assistance patterns, the eight lower limb muscle activities could be decomposed to five basic muscle synergies. The muscle synergies changed little under assistance with appropriate actuation timing and torque magnitude. Besides, co-contraction indexs of soleus and tibialis anterior, rectus femoris and semitendinosus under exoskeleton assistance were higher than normal walking. Our results are expected to help to understand how healthy wearers adjust their neuromuscular control mechanisms to adapt to different exoskeleton assistance patterns, and provide reference to select appropriate assistance to improve walking efficiency.

Analysis of Asymmetric Stress Ratio in Shallow Buried Tunnels

Parametric investigation on the damage behavior of a CFRP omega reinforced panel subjected to asymmetrical flexural load conditions

In this paper, the damage mechanisms of reinforced composite panels subjected to symmetrical and asymmetrical flexural loading conditions have been investigated. The composite components are representative of a regional aircraft fuselage. Three-point bending tests numerical simulations have been used to assess the influence of the different test parameters on the damage behavior of the investigated component. Then, the most representative configuration has been selected for the experimental bending test. the outputs from the numerical simulations, in terms of stiffness and damage onset and propagation, has been employed, in combination with the experimental data, to accurately describe the damage mechanisms associated to the asymmetric application of the load.

Background In the triple jump event, the explosive power, coordination, and specialized performance of lower limb muscles are key factors determining athletes’ performance. However, traditional high load resistance training has limitations in improving athletes’ lower limb coordination and sustained explosive power. Objective The main purpose of the study is to investigate the training effect of low-load resistance combined with single-leg pressurized exercise method on athletes’ lower limb muscle explosive power, coordination, and special performance. Method For the study, twenty male triple jumpers were enlisted and split into ten-person experimental and control groups at random. The training effects of conventional single-leg high load resistance training and low-load resistance mixed with single-leg compression training were compared using the experimental approach. The experimental duration was 8 weeks. Before and after the experiment, the athletes’ lower limb muscle circumference, body composition, lower limb dynamic balance ability, isokinetic strength, counter movement jump, one repetition maximum squats, key performance indicators of lower limb explosive power, and triple jump special scores were tested. Results After an eight-week training period, the experimental group showed significantly greater improvement than the control group across key performance metrics. Specifically, the experimental group showed superior gains in lower limb muscle circumference, dynamic balance, isokinetic peak torque, and maximum power in the countermovement jump ( p < 0.05). Furthermore, their 1RM squat strength and triple jump performance were also significantly enhanced. Conclusion It shows that the low-load resistance combined with single-leg pressurization exercise method can effectively improve the athletes’ lower limb explosive power, coordination, and special performance. This provides a reliable lower limb explosive power training program for athletes and coaches.