Is active sitting as active as we think?

The aim of this study was to compare the biomechanical characteristics of sitting on a stool without a backrest (so as to encourage active sitting), sitting on a conventional office chair and standing in healthy participants. Thirteen healthy participants performed a keyboard-writing task during four (stable and unstable) sitting conditions and standing. Body segment positions and posture, postural sway and muscle activity of neck and trunk muscles were assessed with a motion capture system, a force plate and surface electromyography. The results showed that body segment positions, postural sway and trunk muscle activity were relatively similar for the stools without backrests compared with standing. All sitting conditions showed lower vertical upper body alignment, less anterior pelvic tilt and larger hip angles, compared with standing (p = 0.000). Unexpectedly, the muscle activity levels and total postural sway, sway velocity and sway in M/L and A/P directions were lower (p = 0.000) for the conditions that encouraged active sitting and standing, compared with the conventional office chair conditions.

Practitioner Summary: Thirteen healthy participants performed a keyboard-writing task during different sitting conditions and standing and were analysed regarding posture, postural sway and trunk muscle activity. Surprisingly, less postural sway and less muscle activity were observed during the conditions that encourage active sitting, compared with sitting on a conventional office chair.     

Novel thoraco-lumbo-sacral corset design increases Biering-Sorensen back endurance and alters knee and ankle angles during a box lifting task

Research investigating lumbosacral corset designs and their effects are limited and conflicting. The objective was to compare thoraco-lumbo-sacral support corsets (polyester/nylon: TLSSC-poly and neoprene: TLSSC-neo) with a traditional model (TRAD) and Control. Twenty male, university-aged, healthy, recreationally active, participants performed Biering-Sorensen back endurance (BS) test and box lifting tasks (BL:30 repetitions using 20% body mass). Lower and upper erector spinae and hamstrings electromyography (EMG); trunk-hip, knee, and ankle kinematics as well as endurance time were monitored. With BL, the TLSSC-poly (121.4°±17.9) exhibited 1.9% (p = 0.01), 2.7% (p = 0.003), and 3.7% (p = 0.0003) greater knee flexion than TRAD (119.1°±17.5), TLSSC-neo (116.8°±17.4) and Control (120.1°±17.6) respectively. The TLSSC-poly (101.9°± 8.9) demonstrated significant 3.5% (p = 0.005), 2.2% (p = 0.002) and 1.4% (p = 0.01) greater dorsiflexion than TRAD (103.4°±8.7), TLSSC-neo (104.2°±9.8) and Control (105.7°±7.2) respectively. With BS, TLSSC-poly (137.4-s±31.2, 9.7%, p = 0.018) and TLSSC-neo (133.8-s±32.3, 9.2%, p = 0.006) exhibited significantly longer durations than Control (124.8-s±29.8). Relevance to industry: The TLSSC increased BS endurance and TLSSC-poly increased BL knee and ankle angles, possibly providing benefits for workers, with repeated actions over a full work day.     

Inter-joint sharing of total support moments in the lower extremities during gait in narrow-heeled shoes of different heights

The study aimed to investigate the influence of the base and height of shoe heels on the total support moment (Ms) and individual joint contributions during gait. Fifteen healthy females walked barefoot and with narrow-heeled shoes (heel heights: 3.9, 6.3 and 7.3 cm) while kinematic and kinetic data were measured. Compared with the barefoot condition, the subjects maintained unaltered Ms in the sagittal plane in shod conditions. This was achieved by increasing the knee extensor moment to compensate for the diminished ankle plantarflexor moments in medium and high heel conditions. In the frontal plane, subjects in shod conditions had to sustain an increased Ms for balance control during late single-leg stance with increased knee abductor and ankle pronator moments as a result of the reduced base of the heels. The results will be helpful for future shoe designs to reduce fall risks and prevent relevant musculoskeletal problems     

柔性双轮平衡机器人的动力学建模与分析

提出了一种柔性双轮平衡机器人,其机身具有以一段弹簧作为弹性阻尼的被动俯仰旋转关节．运用拉 格朗日方法建立了此机器人在平面运动的动力学模型．基于此模型,首先证明了柔性双轮平衡机器人在直立平衡点 不稳定和局部可控．其次,分析了关节刚度对线性二次型最优姿态平衡控制系统的影响．结果显示,关节刚度减小 在理论上能够加强系统的鲁棒性,却使得控制系统动态性能下降．本文提出的模型及相关分析为柔性双轮平衡机器 人的设计和控制提供了一定理论依据．     

A wide view auto‐stereoscopic 3D display with an eye‐tracking system for enhanced horizontal viewing position and viewing distance

This paper describes the development of auto‐stereoscopic three‐dimensional (3D) display with an eye‐tracking system for not only the X‐axis (right–left) and Y‐axis (up–down) plane directions but also the Z‐axis (forward–backward) direction. In the past, the eye‐tracking 3D system for the XY‐axes plane directions that we had developed had a narrow 3D viewing space in the Z‐axis direction because of occurrence of 3D crosstalk variation on screen. The 3D crosstalk variation on screen was occurred when the viewer's eye position moved back and forth along the Z‐axis direction. The reason was that the liquid crystal (LC) barrier pitch was fixed and the LC barrier was able to control the only barrier aperture position. To solve this problem, we developed the LC barrier that is able to control the barrier pitch as well as the barrier aperture position in real time, corresponding to the viewer's eye position. As a result, the 3D viewing space has achieved to expand up to 320–1016 mm from the display surface in the Z‐axis direction and within a range of ±267 mm in the X‐axis direction. In terms of the Y‐axis direction, the viewing space is not necessary to be considered, because of a stripe‐shaped parallax barrier.     

Influence of carrying heavy loads on soldiers' posture,movements and gait

Military personnel are required to carry heavy loads whilst marching; this load carriage represents a substantial component of training and combat. Studies in the literature mainly concentrate on physiological effects, with few biomechanical studies of military load carriage systems (LCS). This study examines changes in gait and posture caused by increasing load carriage in military LCS. The four conditions used during this study were control (including rifle, boots and helmet carriage, totalling 8 kg), webbing (weighing 8 kg), backpack (24 kg) and a light antitank weapon (LAW; 10 kg), resulting in an incremental increase in load carried from 8, 16, 40 to 50 kg. A total of 20 male soldiers were evaluated in the sagittal plane using a 3-D motion analysis system. Measurements of ankle, knee, femur, trunk and craniovertebral angles and spatiotemporal parameters were made during self-paced walking. Results showed spatiotemporal changes were unrelated to angular changes, perhaps a consequence of military training. Knee and femur ranges of motion (control, 21.1° ± 3.0 and 33.9° ± 7.1 respectively) increased (p < 0.05) with load (LAW, 25.5° ± 2.3 and 37.8° ± 1.5 respectively). The trunk flexed significantly further forward, confirming results from previous studies. In addition, the craniovertebral angle decreased (p < 0.001) indicating a more forward position of the head with load. It is concluded that the head functions in concert with the trunk to counterbalance load. The higher muscular tensions necessary to sustain these changes have been associated with injury, muscle strain and joint problems.     

Arm lift strength in work space

This study was conducted to determine arm strength values for isometric and isokinetic efforts around the human trunk. Thirty-eight normal young adults (20 male and 18 female) performed a total of 19 tasks. These consisted of one self-selected optimum posture with upright stance and elbows bent at 90 degrees , designated as standard posture for isometric test. In addition, isometric testing was done sagittally symmetrical 30 degrees and 60 degrees lateral planes at half-, three-quarters- and full-reach distances at knuckle height. The isokinetic tests were done between knuckle height and shoulder height in postures identical to isometric tests. The sequence of these tasks was randomised. The peak strength in standard posture was invariably lower than the peak strength at half-reach in isometric condition in all three planes for both sexes with the exception of one condition among females (60 degrees lateral plane, half-reach isometric). Peak and average arm lift strengths of males were significantly higher than those of females (p < 0.01) and ranged between 44% and 71%. For both sexes isometric strength was significantly higher than isokinetic strength (p < 0.01). The peak and average strengths in the sagittal plane were invariably higher than those of asymmetric postures, with one exception among females. With increasing reach distance the strength declined significantly for all conditions among both genders (p < 0.01). The ANOVA showed that the gender, mode of lifting, postural symmetry and reach of lifting, in addition to affecting the peak and average strength individually (p < 0.01), had significant 2-way and 3-way interactions (p < 0.01). All strength values were inter-correlated (p < 0.01). The regressions predicting peak and average strengths from anthropometric characteristics and sagittal plane strengths accounted for 63% to 89% of all variance and were highly significant (p < 0.01).     

Evaluation of circumferential pressure as an intervention to mitigate postural instability induced by localized muscle fatigue at the ankle

Pressure application via taping reportedly improves proprioception, and localized muscle fatigue (LMF) increases postural sway, which may be due to a loss of position sense acuity (PSA). This exploratory study investigated the effects of circumferential pressure (CP) and induced ankle LMF on sway. Fourteen young participants performed fatiguing sub-maximal isotonic plantarflexion exercises. Ankle PSA was determined, and used to categorize participants (i.e. high and low groups). Postural sway during quiet standing was assessed using a force platform, both pre- and post-LMF. CP was applied unilaterally to the dominant leg above the ankle joint. Both CP and LMF resulted in greater sway in the low PSA group. CP did not mitigate LMF effects on sway in the low PSA group, but reduced sway among the high PSA group. Reduced PSA may thus indicate less reliance on somatosensation for balance maintenance.

Relevance to industry

Potential benefits of circumferential pressure were indicated. Specifically, CP at the ankle led to improved postural control in certain individuals, which suggests that pressure application might thereby improve balance maintenance and help reduce occupational fall incidents. Results might help to design occupational interventions (specifically CP or taping) differently for individuals with low vs. high PSA.     

The interrelationship of the thorax and pelvis under varying task constraints

The purpose of this study was to investigate the interrelationship between the thorax and pelvis during coupled movement patterns. Fifty-seven participants were assessed using an infrared motion analysis system to track trunk movement during maximal pelvis and thorax rotations over four trunk inclinations and two pelvic constraint conditions. A repeated-measures multivariate analysis of variance investigated the effects of forward trunk inclination and pelvic constraint on thorax and pelvic rotation. Forward trunk inclination from neutral to 45° resulted in a 46% (p < 0.001) decrease in axial pelvic rotation and a 15% (p < 0.001) decrease in axial thorax rotation with an unconstrained pelvis. A constrained pelvis resulted in a 15% (p < 0.001) decrease in axial thorax rotation. An externally constrained pelvis allowed the thorax to achieve an average of 18° (SD = 2°) greater rotational range of motion across all angles. This study reinforced the importance of allowing the pelvis to rotate during whole body axial rotation tasks.

Practitioner Summary: Results indicated that maximum axial trunk rotation is best achieved in a neutral posture, when the pelvis is allowed to contribute and flexion at the hips should be minimised. For example, if a recumbent task requires rotation of the torso, then the chair seat should be allowed to swivel.     

Online Balance Controllers for a Hopping and Running Humanoid Robot

This paper describes online balance controllers for running in a humanoid robot and verifies the validity of the proposed controllers via experiments. To realize running in the humanoid robot, the overall control structure is composed of an offline controller and an online controller. The main purpose of the online controller is to maintain dynamic stability while the humanoid robot hops or runs. The online controller is composed of the posture balance control in the sagittal plane, the transient balance control in the frontal plane and the swing ankle pitch compensator in the sagittal plane. The posture balance controller makes the robot maintain balance using an inertial measurement unit sensor in the sagittal plane. The transient balance controller makes the robot keep its balance in the frontal plane using gyros attached to each upper leg. The swing ankle pitch compensator prevents the swing foot from hitting the ground at unexpected times while the robot runs forward. HUBO2 was used for the running experiment. It was designed for the running experiment, and is lighter and more powerful than the previous walking robot platform, HUBO. With the proposed controllers, HUBO2 ran forward stably at a maximum speed of 3.24 km/h and this result verified the effectiveness of the proposed algorithm. In addition, in order to show the contribution of the stability, the running performance according to the existence of each controller was described by experiment.     

Lumbar posture and individual flexibility influence back muscle flexion-relaxation phenomenon while sitting

Although numerous studies have documented back muscle flexion-relaxation phenomenon (FRP) in standing postures, few studies have examined the FRP in various seated lumbar postures and individual flexibilities. This study, therefore, recruited 18 male students and assigned to low- and high-flexibility groups (9 in each). Activation of thoracic and lumbar erector spinae (ES) and lumbosacral angles were examined while participants sat in two postures (lordosis and kyphosis) and flexed their trunks at 15°, 30°, 45°, 60°, and maximum flexion. Results showed that kyphotic lumbar posture caused relatively low and unchangeable thoracic and lumbar ES activations, whereas lordotic lumbar posture engendered more contractive and varying thoracic and lumbar ES activations. Flexible participants exhibited higher thoracic ES activation than less flexible participants during lordotic sitting. Thoracic ES seemed to play a compensative role to stabilize the spine in the lordotic sitting posture, especially when the trunk was flexed over 45°. In lordotic lumbar posture, FRP occurred only in the lumbar ES; however, the activation and lumbosacral angles were still higher than those in kyphotic posture. The increased back muscle activation associated with lumbar lordosis may partially share the load on passive interspinous tissues, which are close to the discs during these flexed trunk positions.Relevance to industryThis study suggests that various lumbar postures and individual flexibilities may cause different FRP patterns when sitting. While performing seated tasks, people should exercise caution about the lumbar posture.     

A PI/PID controller for time delay systems with desired closed loop time response and guaranteed gain and phase margins

In this article we present a graphical tuning method of PI/PID controller for first order and second order plus time delay systems using dominant pole placement approach with guaranteed gain margin (GM) and phase margin (PM). The stability equation method and gain phase margin tester have been used to portray constant GM and PM boundaries. The PID controller parameters have been obtained for different dominant poles and plotted graphically in the parameters plane of controller within the specified GM and PM regions. To demonstrate the effectiveness and confirm the validity of the proposed methodology, three examples with numerical simulations are presented.     

Control of posture during tasks representing common work-related postures – a reliability study

Assessment of control of posture using a task battery that represents work-related postural conditions is highly recommended for providing a comprehensive understanding of collective postural demands. However, dearth of evidence exists on the reliability of a task battery, thus precluding its use as an outcome measure in field research. This study investigated the intrasession reliability and systematic variation of force plate derived centre of pressure (COP) measures obtained during repeated performance of a task battery (lifting task, limits of stability and bipedal and unipedal stance). COP signals obtained during each task performance were processed to derive various time-domain COP measures. Statistical analyses revealed that 13 of the 19 COP measures displayed excellent relative (ICC_(2,3) ≥ 0.75) and acceptable absolute reliability (SEM%: ≤ 10). Although COP measures displayed systematic variation, the differences were less or equal to the measurement error, except COP measures of unipedal stance and limits of stability. The chosen task battery is reliable and can be used for comprehensive evaluation of control of posture, in both field and laboratory research.

Practitioner Summary: Repeated evaluation of multiple tasks together sequentially could introduce measurement variability. This study investigated intrasession reliability of a task battery representing common work-related postures. The chosen task battery was found to be reliable with acceptable measurement error and can be used in field research settings for evaluation of control of posture.     

两轮自平衡小车的系统设计与实现

两轮自平衡小车是以倒立摆模型为基础的动态平衡系统,针对系统设计中的车身结构、姿态检测与动态平衡控制等关键问题进行研究.采用一体化轮毂电机作为自平衡小车的驱动单元,设计轻量化车身结构以降低车身重量和能量损耗.控制系统采用含有加速度计、陀螺仪、电子罗盘的9轴姿态检测传感器检测车身姿态角度,利用卡尔曼滤波算法进行数据融合,获得姿态角度的最优估计,借助PID运动控制算法驱动轮毂电机运动,实现自平衡小车车身的动态平衡.通过参数优化,提升了系统的响应速度,将姿态角度估计的误差降低到0.5°以内,实现了两轮小车自主动态平衡功能,为两轮自平衡小车的设计提供了一种简单、可行、低成本的设计方案.     

Globally asymptotically stable saturated PID controllers for a double integrator with constant disturbance

This paper provides a deep insight into the saturated PID control of a double integrator with bounded disturbance. On the basis of the nested saturation functions, a simple PID‐like controller is proposed. The main difficulty in saturation control with bounded disturbances is to prove that the unsaturated regions are invariant. By phase plane and singular perturbation analysis, we prove that the saturation restrictions on the controller can be removed one by one in finite time, and the closed‐loop system can be finally reduced to a nonsaturated PID controlled double integrator. The sufficient conditions for the stability of the closed loop with disturbance are also derived. Finally, numerical simulations are conducted to validate the effectiveness of the proposed control scheme. Copyright © 2012 John Wiley & Sons, Ltd.     

The effects of a lower body exoskeleton load carriage assistive device on limits of stability and postural sway

The study investigated the effects of using a lower body prototype exoskeleton (EXO) on static limits of stability and postural sway. Measurements were taken with participants, 10 US Army enlisted men, standing on a force platform. The men were tested with and without the EXO (15 kg) while carrying military loads of 20, 40 and 55 kg. Body lean to the left and right was significantly less and postural sway excursions and maximal range of movement were significantly reduced when the EXO was used. Hurst values indicated that body sway was less random over short-term time intervals and more random over long-term intervals with the EXO than without it. Feedback to the user's balance control mechanisms most likely was changed with the EXO. The reduced sway and relatively small changes in sway with increasing load weights suggest that the EXO structure may have functioned to provide a bracing effect on the body.     

Prediction accuracy in estimating joint angle trajectories using a video posture coding method for sagittal lifting tasks

This study investigated prediction accuracy of a video posture coding method for lifting joint trajectory estimation. From three filming angles, the coder selected four key snapshots, identified joint angles and then a prediction program estimated the joint trajectories over the course of a lift. Results revealed a limited range of differences of joint angles (elbow, shoulder, hip, knee, ankle) between the manual coding method and the electromagnetic motion tracking system approach. Lifting range significantly affected estimate accuracy for all joints and camcorder filming angle had a significant effect on all joints but the hip. Joint trajectory predictions were more accurate for knuckle-to-shoulder lifts than for floor-to-shoulder or floor-to-knuckle lifts with average root mean square errors (RMSE) of 8.65°, 11.15° and 11.93°, respectively. Accuracy was also greater for the filming angles orthogonal to the participant's sagittal plane (RMSE = 9.97°) as compared to filming angles of 45° (RMSE = 11.01°) or 135° (10.71°). The effects of lifting speed and loading conditions were minimal. To further increase prediction accuracy, improved prediction algorithms and/or better posture matching methods should be investigated.

Statement of Relevance: Observation and classification of postures are common steps in risk assessment of manual materials handling tasks. The ability to accurately predict lifting patterns through video coding can provide ergonomists with greater resolution in characterising or assessing the lifting tasks than evaluation based solely on sampling with a single lifting posture event.     

Development of Human Posture Simulation Method for Assessing Posture Angles and Spinal Loads

Video‐based posture analysis employing a biomechanical model is gaining a growing popularity for ergonomic assessments. A human posture simulation method of estimating multiple body postural angles and spinal loads from a video record was developed to expedite ergonomic assessments. The method was evaluated by a repeated measures study design with three trunk flexion levels, two lift asymmetry levels, three viewing angles, and three trial repetitions as experimental factors. The study comprised two phases evaluating the accuracy of simulating self‐ and other people's lifting posture via a proxy of a computer‐generated humanoid. The mean values of the accuracy of simulating self‐ and humanoid postures were 12° and 15°, respectively. The repeatability of the method for the same lifting condition was excellent (～2°). The least simulation error was associated with side viewing angle. The estimated back compressive force and moment, calculated by a three‐dimensional biomechanical model, exhibited a range of 5% underestimation. The posture simulation method enables researchers to quantify simultaneously body posture angles and spinal loading variables with accuracy and precision comparable to on‐screen posture‐matching methods.     

基于灰色预测的大时滞过程的控制研究

针对传统PID控制对大时滞过程控制效果不佳的情况,采用基于GM(1,1)灰色模型对被控对象系统行为进行预测,并用等维新息、提高原始数据列的光滑度和改变初始条件三者结合的方法对该模型进行改进,得到一个改进的GM(1,1)模型.同时以GM(1,1)模型的发展系数a作为决定预测步长的依据,将其与传统PID结合,组成灰色预测控制系统对大时滞过程进行控制.仿真结果表明,与传统PID控制相比,该方法具有较强的适应性和鲁棒性,控制性能也得到了较明显的改善.