Kinematic and electromyography analysis of paraplegic gait with the assistance of mechanical orthosis and walker

Objective: To investigate the kinematics, functional sub-tasks, and excitation levels of the trunk and upper extremity muscles of paraplegic subjects during walker-assisted locomotion. Design: Retrospective cross-sectional study. Setting: Gait analysis laboratory. Participants: Eight individuals with spinal cord injury at T12, lower extremity motor score less than 4, and capable of walking independently with the assistance of ankle-foot orthosis and walker. Main Outcome Measures: Kinematics of pelvis, trunk, shoulder and elbow; trajectory of center of mass; and electromyography (EMG) activity of trunk and upper extremity muscles during gait. Results: Four subtasks were characterized for each locomotion step, based on the kinetics and kinematics data: (1) balance adjustment, (2) walker propulsion, (3) leg raising, and (4) leg swing. The latter two involved large lateral maneuvres by the trunk and pelvis and appeared to be the most skill- and muscle activity-demanding subtasks. The main muscles contributing into these subtasks were the ipsilateral paraspinal and abdominal muscles, as well as the contralateral scapulothoracic and shoulder girdle muscles, with EMG intensities significantly higher than their minimum mean intensities (P < 0.05) and those of the contralateral side (P < 0.05). Conclusions: Our results provide more insight into the functional sub-tasks and muscular demands of walker-assisted paraplegic gait that can help to design appropriate muscle strengthening programs, as well as developing more effective gait orthoses.

Robust adaptive Lyapunov-based control of hepatitis B infection

A new robust adaptive controller is developed for the control of the hepatitis B virus (HBV) infection inside the body. The non-linear HBV model has three state variables: uninfected cells, infected cells and free viruses. A control law is designed for the antiviral therapy such that the volume of infected cells and the volume of free viruses are decreased to their desired values which are zero. One control input represents the efficiency of drug therapy in inhibiting viral production and the other control input represents the efficiency of drug therapy in blocking new infection. The proposed controller ensures the stability and robust performance in the presence of parametric and non-parametric uncertainties (and/or bounded disturbances). The global stability and tracking convergence of the process are investigated by employing the Lyapunov theorem. The performance of the proposed controller is evaluated using simulations by considering different levels of uncertainties. Based on the obtained results, the proposed strategy can achieve its desired objectives with different cases of uncertainties.

Biomechanical simulation of eye-airbag impacts during vehicle accidents

Airbags are safety devices in vehicles effectively suppressing passengers' injuries during accidents. Although there are still many cases of eye injuries reported due to eye-airbag impacts in recent years. Biomechanical approaches are now feasible and can considerably help experts to investigate the issue without ethical concerns. The eye-airbag impact-induced stresses/strains in various components of the eye were found to investigate the risk of injury in different conditions (impact velocity and airbag pressure). Three-dimensional geometry of the eyeball, fat and bony socket as well as the airbag were developed and meshed to develop a finite element model. Nonlinear material properties of the vitreous body and sclera were found through the in vitro tests on ovine samples and for the other components were taken from the literature. The eye collided the airbag due to the velocity field in the dynamic explicit step in Abaqus. Results of compression tests showed a nonlinear curve for vitreous body with average ultimate stress of 22 (18-25) kPa. Tensile behavior of sclera was viscoelastic nonlinear with ultimate stresses changing from 2.51 (2.3-2.7) to 4.3 (4-4.6) MPa when loading strain rate increased from 10 to 600 mm/min. Sclera, ciliary body, cornea and lens were the eye components with highest stresses (maximum stress reached up to 9.3 MPa). Cornea, retina and choroid experienced the highest strains with the maximum up to 14.1%. According to the previously reported injury criteria for cornea, it was at high risk of injury considering both stress and strains. Reduced pressure of the airbag was beneficial decreased stress of all components. Comprehensive investigations in this area can disclose biomechanical behavior of the eye during eye-airbag impact. Effective guidelines can be drawn for airbag design for instance the airbag pressure which reduces risk of eye injury.

Designing instrumented walker to measure upper-extremity's efforts: A case study

The high prevalence of shoulder pain in using walkers in patients who have spinal cord injury (SCI). Also, the limited options available to economically measure grip forces in walkers, which drove the need to create one. This article describes a method to obtain upper-extremities' forces and moments in a person with SCI by designing an appropriate instrumented walker. First, since the commercial multidirectional loadcells are too expensive, custom loadcells are fabricated. Ultimately, a complete gait analysis by means of VICON motion analysis and using inverse dynamic method has been held to measure upper-extremities' efforts. The results for a person with SCI using a two-wheel walker in low and high heights and a basic walker show that there are higher shoulder and elbow flexion-extension moments and also higher shoulder forces in superior-inferior direction and higher elbow and wrist forces in anterior-posterior directions. The results are not much different in using two different types of walker. By using the proposed method, upper-extremities' forces and moments were obtained and the results were compared to each other in using two different walkers.

Role and Significance of Trunk and Upper Extremity Muscles in Walker-Assisted Paraplegic Gait: A Case Study

Background and Purpose: Understanding the role and significance of trunk and upper extremity muscles in paraplegic gait can help in designing more effective assistive devices for these patients and also provides valuable information for improving muscle strengthening programs. Methods: In a patient with a spinal cord injury (SCI) who could walk independently (rating scale of ambulatory capacity, 9) with the aid of bilateral ankle-foot orthosis and a walker, the kinematics, kinetics and electromyographic (EMG) activities of 16 muscles from the trunk and upper and lower extremities were recorded during gait. The onset, cessation, and duration of the EMG signal were associated with the 4 phases of each step, distinguished based on the kinematics results. Results: It was found that the reciprocating activation pattern of the quadratus lumborum, latissimus dorsi, pectoralis major, and lower trapezius is responsible for trunk extension during the balance adjustment phase, leg unload and foot clearance creation during the leg raising phase, and propulsion force generation during the leg swing phase. Conclusion: The continuous activation of the rectus abdominis and erector spinae within the gait cycle helps stabilize the thorax and acts in reverse, that is, fixes the proximal joint and moves the distal limb. The shoulder girdle muscles contribute to the leg's unloading and then smooth landing during leg raising and leg swing phases, respectively.

Modular neuromuscular control of human locomotion by central pattern generator

The central pattern generators (CPG) in the spinal cord are thought to be responsible for producing the rhythmic motor patterns during rhythmic activities. For locomotor tasks, this involves much complexity, due to a redundant system of muscle actuators with a large number of highly nonlinear muscles. This study proposes a reduced neural control strategy for the CPG, based on modular organization of the co-active muscles, i.e., muscle synergies. Four synergies were extracted from the EMG data of the major leg muscles of two subjects, during two gait trials each, using non-negative matrix factorization algorithm. A Matsuoka׳s four-neuron CPG model with mutual inhibition, was utilized to generate the rhythmic activation patterns of the muscle synergies, using the hip flexion angle and foot contact force information from the sensory afferents as inputs. The model parameters were tuned using the experimental data of one gait trial, which resulted in a good fitting accuracy (RMSEs between 0.0491 and 0.1399) between the simulation and experimental synergy activations. The model׳s performance was then assessed by comparing its predictions for the activation patterns of the individual leg muscles during locomotion with the relevant EMG data. Results indicated that the characteristic features of the complex activation patterns of the muscles were well reproduced by the model for different gait trials and subjects. In general, the CPG- and muscle synergy-based model was promising in view of its simple architecture, yet extensive potentials for neuromuscular control, e.g., resolving redundancies, distributed and fast control, and modulation of locomotion by simple control signals.

A Robotic Model of Transfemoral Amputee Locomotion for Design Optimization of Knee Controllers

A two-dimensional, seven link, nine degrees of freedom biped model was developed to investigate the dynamic characteristics of normal and transfemoral amputee locomotion during the entire gait cycle. The equations of motion were derived using the Lagrange method and the stance foot-ground contact was simulated using a five-point penetration model. The joint driving torques were obtained using forward dynamic optimization of the normal human gait and applied to the intact joints of the amputee. Three types of motion controllers; frictional, elastic and hydraulic were considered for the prosthetic joints of the amputee and their design parameters were optimized to achieve the closest kinematics to that of the normal gait. It was found that, if optimally designed, all three passive controllers could reasonably reproduce a normal kinematical pattern in the swing phase. However, the stance phase kinematics could only be replicated by the hydraulic and elastic controllers; the performance of the latter was highly sensitive to the design parameters. It was concluded that an appropriately designed hydraulic motion controller can provide reasonably normal kinematics and reliable stability for stance knee flexion prostheses.