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This paper investigates deteriorations in knee and ankle dynamics during running. Changes in lower limb accelerations are analyzed by a wearable musculoskeletal monitoring system. The system employs a machine-learning technique to classify joint stiffness. A maximum-entropy-rate method is developed to select the most relevant features. Experimental results demonstrate that distance travelled and energy expended can be estimated from observed changes in knee and ankle motions during 5-km runs. [ABSTRACT FROM AUTHOR]

This paper presents a control system for a powered transtibial prosthesis that provides stair ascent and descent capability, as well as ability for user-controlled transitions between walking, standing, stair ascent, and stair descent. The control system was implemented on a powered prosthesis and evaluated on a single unilateral transtibial amputee subject. The ability of the prosthesis to provide appropriate functionality during stair ascent and descent was assessed by comparing gait kinematics and kinetics of the prosthesis to those of a passive dynamic elastic response prosthesis and those of a set of non-amputee subjects. Data from the assessment indicates that the powered prosthesis is able to provide some desirable stair ascent and stair descent characteristics, relative to the passive prosthesis. [ABSTRACT FROM PUBLISHER]

In this paper, we present the mechanical design, control algorithm, and functional evaluation of a quasi-passive compliant stance control knee-ankle-foot orthosis. The orthosis implements a spring in parallel with the knee joint during the stance phase of the gait and allows free rotation during the swing phase. The design is inspired by the moment-angle analysis of the knee joint revealing that the knee function approximates that of a linear torsional spring in the stance phase of the gait. Our orthosis aims to restore the natural function of a knee that is impaired by injury, stroke, post-polio, multiple sclerosis, spinal cord injury, patellofemoral pain syndrome, osteoarthritis, and others. Compared with state-of-the-art stance control orthoses, which rigidly lock the knee during the stance phase, the described orthosis intends to provide the natural shock absorption function of the knee in order to reduce compensatory movements both in the affected and unaffected limbs. Preliminary testing on three unimpaired subjects showed that compliant support of the knee provided by the orthosis explained here results in higher gait speed as well as more natural kinematic profiles for the lower extremities when compared with rigid support of the knee provided by an advanced commercial stance control orthosis. [ABSTRACT FROM AUTHOR]

Joint stiffness, the dynamic relationship between the angular position of a joint and the torque acting about it, describes the dynamic, mechanical behavior of a joint during posture and movement. Joint stiffness arises from both intrinsic and reflex mechanisms, but the torques due to these mechanisms cannot be measured separately experimentally, since they appear and change together. Therefore, the direct estimation of the intrinsic and reflex stiffnesses is difficult. In this paper, we present a new, two-step procedure to estimate the intrinsic and reflex components of ankle stiffness. In the first step, a discrete-time, subspace-based method is used to estimate a state-space model for overall stiffness from the measured overall torque and then predict the intrinsic and reflex torques. In the second step, continuous-time models for the intrinsic and reflex stiffnesses are estimated from the predicted intrinsic and reflex torques. Simulations and experimental results demonstrate that the algorithm estimates the intrinsic and reflex stiffnesses accurately. The new subspace-based algorithm has three advantages over previous algorithms: 1) It does not require iteration, and therefore, will always converge to an optimal solution; 2) it provides better estimates for data with high noise or short sample lengths; and 3) it provides much more accurate results for data acquired under the closed-loop conditions, that prevail when subjects interact with compliant loads. [ABSTRACT FROM PUBLISHER]

The control of human walking can be temporarily modified by applying forces to the leg. To study the neural mechanisms underlying this adaptive capacity, a device delivering controlled forces and high-velocity displacements to the ankle was designed. A new solution, involving a closed circuit hydraulic system composed of two cylinders (master-slave) mutually connected by hoses and controlled by an electric motor was preferred over classical mechanical/electrical approaches. The slave cylinder delivers desired torques to the ankle using a light weight, custom-designed ankle-foot orthosis. This electrohydraulic orthosis (EHO) can produce several types of force fields during walking, including constant, position-dependent, and phase-dependent. With phase-dependent force fields, active torque cancellation maintains low-residual torques (≤1.85 Nm root mean square) outside of the zone of force application for walking speeds ranging from 0.2 to 4.5 km/h. Rapid ankle stretches/unloads (>200°/s) can also be produced alone or during force field application, and elicited proprioceptive reflexes in ankle muscles. In conclusion, the EHO is capable of delivering controlled force fields and of activating proprioceptive reflexes during human walking. It will provide the flexibility needed to test the adaptability of healthy and pathological gait control, and to address some of its underlying neural mechanisms. [ABSTRACT FROM AUTHOR]