Biomechanical Strategies for Obstacle Crossing in Patients with Anterior Cruciate Ligament Deficiency

The current study aimed to investigate the biomechanical control strategies in patients with anterior cruciate ligament deficiency (ACLD) when crossing obstacles of different heights. Eighteen patients with unilateral ACLD and sixteen age-matched healthy controls were recruited. They crossed obstacles of heights of 10%, 20% and 30% of their leg lengths at a self-selected pace while the kinematic and kinetic data were measured and analyzed using inverse dynamics analysis. Patients with ACLD were found to avoid using the quadriceps on both affected and unaffected sides during stance phase. Training programs on both quadriceps are needed for more efficient rehabilitation of the patients with unilateral ACLD

Influence of Step Length and Cadence on the Sharing of the Total Support Moments Between the Lower Limbs During Level Walking

The current study aimed to investigate the effects of walking speed on the inter-limb sharing of whole body support in terms of total support moments (Ms) during walking. A multiple linear regression model was conducted to explore the relationship between gait speed in terms of step length and cadence, and the difference of the first and second peaks of the Ms (DMs) during walking. The DMs were found to increase with either increased step length or cadence. Walking with greater speed relied more on the leading limb to provide support for the forward progression of the body. In addition, variations of gait speed parameters affected the load-sharing pattern between the lower limbs during weight transfer of walking. Gait speed parameters have to be taken as covariates when analysing the coordination of the kinetics between lower limbs

The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure

Control of body's center of mass motion relative to center of pressure during uphill walking in the elderly

Uphill walking places more challenges on the locomotor system than level walking does when the two limbs work together to ensure the stability and continuous progression of the body over the base of support. With age-related degeneration older people may have more difficulty in maintaining balance during uphill walking, and may thus experience an increased risk of falling. The current study aimed to investigate using gait analysis techniques to determine the effects of age and slope angles on the control of the COM relative to the COP in terms of their inclination angles (IA) and the rate of change of IA (RCIA) during uphill walking. The elderly were found to show IAs similar to those of the young, but with reduced self-selected walking speed and RCIAs (P < 0.05). After adjusting for walking speed differences, the elderly showed significantly greater excursions of IA in the sagittal plane (P < 0.05) and increased RCIA at heel-strike and during single limb support (SLS) and double limb support (DLS) in the sagittal plane (P < 0.05), and increased RCIA at heel-strike in the frontal plane (P < 0.05). The RCIAs were significantly reduced with increasing slope angles (P < 0.05). The current results show that the elderly adopted a control strategy different from the young during uphill walking, and that the IA and RCIA during walking provide a sensitive measure to differentiate individuals with different balance control abilities. The current results and findings may serve as baseline data for future clinical and ergonomic applications. (C) 2015 Elsevier B.V. All rights reserved

Redistribution of intra- and inter-limb support moments during downhill walking on different slopes

Downhill walking presents a greater risk of falling as a result of slipping or loss of balance in comparison with level walking. The current study aimed to investigate the effects of inclination angles on the intra-limb (inter-joint) and inter-limb sharing of the body support during downhill walking for a better understanding of the associated control strategy. Fifteen young male adults (age: 32.6 + 5.2 years, height: 168.9 +/- 5.5 cm, mass: 68.4 +/- 8.7 kg) performed level and downhill walking while their kinematic and kinetic data were measured for calculating joint moments and total support moments of the lower limbs using inverse dynamics analysis. The peak total support moments of both the leading and trailing limbs increased with increasing inclination angles (p < 0.05) with different sharing patterns among individual joints. Being the major contributor to the peak total support moment during early single-limb support, the contribution of the knee remained unaltered (p > 0.05), but the contributions of the hip increased with reduced contributions from the ankle (p < 0.05). For the increased peak total support moment during late single-limb support, the intra-limb sharing changed from a major ankle contribution to a major knee contribution strategy. The hip contribution was also increased (p < 0.05) but the hip flexor moment remained unaltered (p > 0.05). During double-limb support, the main contributor to the whole body support changed from the trailing limb to the leading limb with increasing inclination angles (p < 0.05). (C) 2013 Elsevier Ltd. All rights reserved

Influence of inclination angles on intra- and inter-limb load-sharing during uphill walking

Uphill walking is an inevitable part of daily living, placing more challenges on the locomotor system with greater risk of falls than level walking does. The current study aimed to investigate the effects of inclination angles on the inter-joint and inter-limb load-sharing during uphill walking in terms of total support moment and contributions of individual joint moments to the total support moment. Fifteen young adults walked up walkways with 0 degrees, 5 degrees, 10 degrees and 15 degrees of slope while kinematic and kinetic data were collected and analyzed. With increasing inclination angles, the first peak of the total support moment was increased with unaltered individual joint contributions, suggesting an unaltered inter-joint control pattern in the leading limb to meet the increased demands. The second peak of the total support moment remained unchanged with increasing inclination angles primarily through a compensatory redistribution of the hip and knee moments. During DLS, the leading limb shared the majority of the whole body support moments. The current results reveal basic intra-and inter-limb load-sharing patterns of uphill walking, which will be helpful for a better understanding of the control strategies adopted and for subsequent clinical applications. (C) 2013 Elsevier B. V. All rights reserved

Influence of Inclination Angles and Aging on Biomechanics during Slope Walking

斜坡行走為日常生活行動不可或缺的一部分，然而行走於斜坡上對於下肢造成更多挑戰。完整的斜坡行走生物力學分析有助於設計步態訓練或者預防跌倒之方法。本研究已建立年輕人於行走不同坡度斜坡時之完整下肢動力學資料，並且探討其下肢關節間以及兩腳間之協調策略，並進一步探討老年人於行走不同斜坡時之下肢生物力學。結果顯示年輕人利用增加骨盆前傾與軀幹屈曲之策略進行上坡走路，反之於下坡時利用骨盆後傾之方式行走。這些策略改變了下肢不同關節之分配與負擔。此外本研究並發現行走於平地、上坡與下坡各有明顯不同的下肢分配協調策略，下肢任一環節出問題皆會影響上下坡行走之表現。而本研究更進一步發現老年人利用骨盆更前傾但減少軀幹屈曲之策略進行上下斜坡，此策略可使老年人以保守的方式上下坡，如減少步距以及保持身體質心維持在軀幹中軸附近。此外，老年人面對斜坡之趨勢與年輕人不同，老年人以增加髖關節比重的方式面對增加坡度時所造成的負擔。而於研究老年人於行走斜坡之動態平衡的結果顯示，老年人能維持與年輕人相同前後重心傾角，但其行走速度較慢，因此若老年人於斜坡增加行走速度時，將會使前後重心傾角變大而增加跌倒之風險。Slope walking is an inevitable part of daily living, placing more challenges on the locomotor system than level walking does. Investigating kinematics, kinetics, intra- and inter-limb load sharing patterns of the locomotor system as well as the whole body dynamic balance control during slope walking may help in devising strategies for gait retraining and fall prevention in the elderly. The work was carried out by a series of studies on the 3D kinetics, intra- and inter-limb load sharing of the lower limbs, and dynamic balance during slope in the young and elder subjects. The results showed that the young subjects increased the anterior tilt of the pelvis and the trunk flexion during uphill walking but increased the posterior tilt of the pelvis during downhill walking. The modulated moments resulted in varied mechanical demands at the lower limb joints. Distinct intra- and inter-limb load-sharing strategies were found in level, uphill and downhill walking. However, greater anterior tilt of the pelvis but lesser trunk flexion were found in the elderly during slope walking. The kinematic configuration showed that the elderly adopted a conservative strategy to decrease the step length and thus maintain the body’s COM control in the sagittal plane. The elderly were found to perform different trend with increasing slope angles compared with the young, and showed a hip strategy to meet the increased demand during slope walking. Furthermore, the elderly were found to walk with greater excursions of boby’s center of mass if they walked at the same speed as the young adults did. It indicated that the elderly suffered greater risk of sagittal instability during slope walking.中文摘要 ii Abstract iii Acknowledgements v Table of Content vii List of Figure xi List of Table xvi Chapter 1. Introduction 1 1.1 Biomechanics of Slope Walking 1 1.1.1 Overview 1 1.1.2 Gait Mechanics of Slope Walking in Young Adults 2 1.1.3 Limitations of Previous Studies 3 1.2 Approaches of Gait Analysis to Study Slope Walking 5 1.2.1 The Total Support Moment 6 1.2.2 Dynamic Stability 7 1.3 Influence of Aging on Biomechanics of the Locomotor System 10 1.3.1 Aging and Falls on Inclined Surfaces 10 1.3.2 Physiological Changes with Aging 11 1.3.3 Biomechanical Changes of Aging during Functional Activities 13 1.4 Biomechanics of Slope Walking in the Elderly 14 1.5 Aims of this Dissertation 15 Chapter 2. Materials and Methods 18 2.1 Subjects 18 2.1.1 Healthy young subjects 18 2.1.2 Elderly subjects 19 2.2 Instruments 19 2.3 Experiments 22 2.4 Biomechanical Analysis Models 24 2.4.1 Coordinate Systems 25 2.4.2 Anthropometric Parameters 30 2.4.3 Inverse Dynamics Analysis 31 2.4.4 Body’s COM Model 39 2.5 Data Analysis 40 2.5.1 Spatial-Temporal Variables 40 2.5.2 Kinematic Variables 40 2.5.3 Kinetic Variables 41 2.5.4 Variables of the Total Support Moment 42 2.5.5 COM-COP Variables 43 2.5.6 Statistical Analysis 46 Chapter 3. Biomechanics of the Locomotor Systems in Young Adults during Slope Walking7 48 3.1 Subjects 49 3.2 Data Analysis 49 3.3 Results 50 3.3.1 Spatial-temporal variables 50 3.3.2 Trunk, pelvic and joint kinematics 52 3.3.3 Joint Forces 57 3.3.4 Joint Moments 63 3.3.5 Joint Impulses 69 3.4 Discussion 72 3.5 Conclusions 76 Chapter 4. Influence of Inclination Angles on Intra- and Inter-limb Load Sharing during Slope Walking1, 4 77 4.1 Subjects 78 4.2 Data Analysis 78 4.3 Results 79 4.3.1 Joint angles and moments, and lever-arm lengths of GRF 79 4.3.2 Total support moment (Ms) and individual joint contributions (CMs) 84 4.3.3 Inter-limb contributions to whole body support moment (WMs) 85 4.4 Discussion 92 4.5 Conclusions 95 Chapter 5. Comparisons of the Biomechanics in the Locomotor System between Young Adults and the Elderly during Slope Walking 97 5.1 Subjects 97 5.1.1 Healthy young subjects 97 5.1.2 Elderly subjects 98 5.2 Data Analysis 98 5.3 Results 99 5.3.1 Spatial-temporal variables 99 5.3.2 Trunk, pelvic and joint kinematics 101 5.3.3 Joint Forces 102 5.3.4 Joint Moments 109 5.3.5 Joint Impulses 109 5.4 Discussion 116 5.5 Conclusions 118 Chapter 6. Redistributions of Intra- and Inter-limb Load Sharing of the Locomotor System in the Elderly during Slope Walking 120 6.1 Subjects 120 6.1.1 Healthy young subjects 120 6.1.2 Elderly subjects 121 6.2 Data Analysis 121 6.3 Results 122 6.3.1 Joint angles and moments 122 6.3.2 Total support moment (Ms) and individual joint contributions (CMs) 128 6.3.3 Inter-limb contributions to whole body support moment (WMs) 129 6.4 Discussion 134 6.5 Conclusions 136 Chapter 7. Control of Body’s Center of Mass Motion Relative to Center of Pressure During Slope Walking in the Young and Elderly Adults 138 7.1 Subjects 139 7.1.1 Healthy young subjects 139 7.1.2 Elderly subjects 139 7.2 Data Analysis 140 7.3 Results 141 7.4 Discussion 152 7.5 Conclusions 155 Chapter 8. Conclusions and Suggestions 156 8.1 Conclusions 156 8.1.1 Biomechanics of the Locomotor Systems in Young Adults during Slope Walking 156 8.1.2 Changes of Intra- and Inter-limb Load-sharing in the Young Adults When Walking on Different Slopes 157 8.1.3 Comparisons of the Biomechanics in the Locomotor System between Young Adults and the Elderly during Slope Walking 158 8.1.4 Redistributions of Intra- and Inter-limb Load Sharing of the Locomotor System in the Elderly during Slope Walking 159 8.1.5 Control of Body’s Center of Mass Motion Relative to Center of Pressure During Slope Walking in the Young and Elderly Adults 160 8.2 Suggestions and Further Studies 160 8.2.1 Clinical Applications 161 8.2.2 Future Studies 161 Bibliography 163 Appendix: Publication 168 (A) Refereed Journal Article 168 (B) Proceeding Article and Conference Presentations 16

Tendon release reduced joint stiffness with unaltered leg stiffness during gait in spastic diplegic cerebral palsy.

Biomechanical deviations at individual joints are often identified by gait analysis of patients with cerebral palsy (CP). Analysis of the control of joint and leg stiffness of the locomotor system during gait in children with spastic diplegic CP has been used to reveal their control strategy, but the differences between before and after surgery remain unknown. The current study aimed to bridge the gap by comparing the leg stiffness-both skeletal and muscular components-and associated joint stiffness during gait in 12 healthy controls and 12 children with spastic diplegic CP before and after tendon release surgery (TRS). Each subject walked at a self-selected pace on a 10-meter walkway while their kinematic and forceplate data were measured to calculate the stiffness-related variables during loading response, mid-stance, terminal stance, and pre-swing. The CP group altered the stiffness of the lower limb joints and decreased the demand on the muscular components while maintaining an unaltered leg stiffness during stance phase after the TRS. The TRS surgery improved the joint and leg stiffness control during gait, although residual deficits and associated deviations still remained. It is suggested that the stiffness-related variables be included in future clinical gait analysis for a more complete assessment of gait in children with CP

Leg and Joint Stiffness in Children with Spastic Diplegic Cerebral Palsy during Level Walking

<div><p>Individual joint deviations are often identified in the analysis of cerebral palsy (CP) gait. However, knowledge is limited as to how these deviations affect the control of the locomotor system as a whole when striving to meet the demands of walking. The current study aimed to bridge the gap by describing the control of the locomotor system in children with diplegic CP in terms of their leg stiffness, both skeletal and muscular components, and associated joint stiffness during gait. Twelve children with spastic diplegia CP and 12 healthy controls walked at a self-selected pace in a gait laboratory while their kinematic and forceplate data were measured and analyzed during loading response, mid-stance, terminal stance and pre-swing. For calculating the leg stiffness, each of the lower limbs was modeled as a non-linear spring, connecting the hip joint center and the corresponding center of pressure, with varying stiffness that was calculated as the slope (gradient) of the axial force vs. the deformation curve. The leg stiffness was further decomposed into skeletal and muscular components considering the alignment of the lower limb. The ankle, knee and hip of the limb were modeled as revolute joints with torsional springs whose stiffness was calculated as the slope of the moment vs. the angle curve of the joint. Independent t-tests were performed for between-group comparisons of all the variables. The CP group significantly decreased the leg stiffness but increased the joint stiffness during stance phase, except during terminal stance where the leg stiffness was increased. They appeared to rely more on muscular contributions to achieve the required leg stiffness, increasing the muscular demands in maintaining the body posture against collapse. Leg stiffness plays a critical role in modulating the kinematics and kinetics of the locomotor system during gait in the diplegic CP.</p></div