Increase in Leg Stiffness Reduces Joint Work During Backpack Carriage Running at Slow Velocities
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Optimal tuning of leg stiffness has been associated with better running economy. Running with a load is energetically expensive, which could have a significant impact on athletic performance where backpack carriage is involved. The purpose of this study was to investigate the impact of load magnitude and velocity on leg stiffness. We also explored the relationship between leg stiffness and running joint work. Thirty-one healthy participants ran overground at 3 velocities (3.0, 4.0, 5.0 m·s-1), whilst carrying 3 load magnitudes (0%, 10%, 20% weight). Leg stiffness was derived using the direct kinetic-kinematic method. Joint work data was previously reported in a separate study. Linear models were used to establish relationships between leg stiffness and load magnitude, velocity, and joint work. Our results found that leg stiffness did not increase with load magnitude. Increased leg stiffness was associated with reduced total joint work at 3.0 m·s-1, but not at faster velocities. The association between leg stiffness and joint work at slower velocities could be due to an optimal covariation between skeletal and muscular components of leg stiffness, and limb attack angle. When running at a relatively comfortable velocity, greater leg stiffness may reflect a more energy efficient running pattern.Keywords:
Backpack
Joint stiffness
Joint stiffness
Lattice (music)
Structural Stability
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Weak stiffness and insufficient kinematic accuracy of industrial robot obstruct its application in precision machining. Before enhancing machining accuracy by introducing stiffness compensation model, the influence of robot weak stiffness on machining accuracy should be identified. This paper presents an evaluation on the spatial stiffness behavior of end effector by varying joint angles. The coupling relationship between joint stiffness and Cartesian stiffness is first generalized. Based on the calculation on joint stiffness values, simulations focused on the spatial behavior of end effector stiffness are then performed. Simulation results indicate that dramatically stiffness mutations of end effector occur in some spatial position.
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Human walking has been described by spring model recently. It has been verified that the stiffness of the spring model increases as the walking speed increases. However, there has been no study on the physiological meaning or the reason to the stiffness increase of the spring model as the waking speed increases. In this study, we will investigate how the stiffness increase of spring model represents the behavior of human leg and joint stiffness. We established that the increase in joint stiffness makes the leg stiffness to increase for leg segment model, especially knee joint stiffness. To verify the leg stiffness change, the joint stiffness change of human should be examined. If the result shows that the increase of the joint stiffness as walking speed to increase, this feature can be used to make the walking assistance system using the joint stiffness variation to the walking speed.
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The variable-stiffness joint (VSJ) plays an important role in creating compliant and powerful motions. This paper presents a novel wire-driven VSJ based on a permanent magnetic mechanism (PMM). The proposed joint regulates the joint stiffness with lower energy consumption through a wide range via the permanent magnetic mechanism. This effect possibly depends on the novel nonlinear combination of a permanent magnet-spring and wire-driven system that achieves the same stiffness with lower wire tension. A trapezoidal layout of the joint is proposed. Because of the relationship among the stiffness, the position of the joint and the stiffness of the PMM, the stiffness model is also been established. Based on this model, the decoupling controller is built to independently control the position and stiffness of the joint. Experiments show that the VSJPMM achieves position and stiffness independently and also reduces energy and power required to regulate the stiffness compared with the traditional approach. In addition, the proposed mechanism displays a powerful motion and short stiffness adjustment time.
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In this paper, we describe the stiffness of a grasp as a function of grasp configuration, grasp forces and joint stiffness of the fingers. The effects caused by the change of joint configuration is included in the computation of the joint stiffness in terms of Stiffness Induced from Configuration Change and Force (SICC). Based on the analysis, the Decentralized Object Stiffness Control (DOSC) method is proposed so as to achieve the desired overall grasp stiffness. The effects of SICC at the joint stiffness and the performance of the proposed stiffness control.
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Shear-wave (SW) ultrasound elastography is both a clinical and research tool that is increasingly being used to quantify the material properties of muscle. However, how SW velocity relates to stiffness changes on the joint- and muscle-levels is poorly understood. Therefore, the purpose of this work was to develop a biomechanical model to estimate plantar flexor muscle stiffness, and measure joint stiffness, joint-based estimates of muscle stiffness, and medial gastrocnemius (MG) SW velocity under different activations (0, 20, and 40%) to quantify the relationships between 1) joint stiffness and joint-based estimates of muscle stiffness; 2) joint stiffness and MG SW velocity; and 3) joint-based estimates of muscle stiffness and MG SW velocity. Our main findings include strong relationships between 1) joint stiffness and joint-based estimates of muscle stiffness (R 2 = 0.70) and 2) joint stiffness and MG SW velocity (R 2 = 0.66), and a weak relationship between joint-based estimates of muscle stiffness and MG SW velocity (R 2 = 0.24). These findings further our understanding of SW velocity measures in muscle and provide a biomechanical model to decompose muscle stiffness from joint stiffness.
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Muscle stiffness
Biomechanics
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Joint stiffness causes posture movement restriction. However, how joint stiffness responds towards imbalance still remain unclear. The objective was to observe the relationship between the joint stiffness value with balance ability and the efficient amount of stiffness required to maintain posture sway. Moreover, the effects of limited sensory inputs were also discovered. The joint motion at different external perturbations was recorded when different sensory inputs were applied. The results showed that the measurements of joint stiffness displayed imbalance; whereby, less-balanced individuals produced a high stiffness value correlating with the functional reach test (FRT) score. Furthermore, the stiffness value at the joints produced a significant difference with different sensory conditions and when various perturbation frequencies were applied (p < 0.05). The stiffness ratio between joints was also obtained. This study had successfully acquired the correlation between joint stiffness with balance ability, sensory inputs and joint synergy which crucial to maintain the posture balance.
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This paper introduces the category of joint in shield tunneling assembled linging,and details the development of joint model in analysis.Then it also sums up the influence factors of joint stiffness.Lastly,refined researches for joint with FEM method are indicated and its feasibility and effectivity is mentioned in size effect of the segment joint.
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The control of joint stiffness is a fundamental mechanism used to control human movements. While many studies have observed how stiffness is modulated for tasks involving shoulder and elbow motion, a limited amount of knowledge is available for wrist movements, though the wrist plays a crucial role in manipulation. We have developed a computational framework based on a realistic musculoskeletal model, which allows one to calculate the passive and active components of the wrist joint stiffness. We first used the framework to validate the musculoskeletal model against experimental measurements of the wrist joint stiffness, and then to study the contribution of different muscle groups to the passive joint stiffness. We finally used the framework to study the effect of muscle cocontraction on the active joint stiffness. The results show that thumb and finger muscles play a crucial role in determining the passive wrist joint stiffness: in the neutral posture, the direction of maximum stiffness aligns with the experimental measurements, and the magnitude increases by 113% when they are included. Moreover, the analysis of the controllability of joint stiffness showed that muscle cocontraction positively correlates with the stiffness magnitude and negatively correlates with the variability of the stiffness orientation (p < 0.01 in both cases). Finally, an exhaustive search showed that with appropriate selection of a muscle activation strategy, the joint stiffness orientation can be arbitrarily modulated. This observation suggests the absence of biomechanical constraints on the controllability of the orientation of the wrist joint stiffness.
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Describes the stiffness of a grasp as a function of grasp configuration, grasping forces and joint stiffness of the fingers. The effects caused by the change of joint configuration is included in the computation of the joint stiffness in terms of stiffness induced from configuration change and force (SICC). Based on the analysis, the decentralized object stiffness control (DOSC) method is proposed so as to achieve the desired overall grasp stiffness. The effects of SICC at the joint stiffness and the performance of the proposed stiffness control method are experimentally verified using a two fingered robot hand.
Joint stiffness
Robot hand
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