Simultaneous estimation of human and exoskeleton motion: A simplified protocol

Adequate benchmarking procedures in the area of wearable robots is gaining importance in order to compare different devices on a quantitative basis, improve them and support the standardization and regulation procedures. Performance assessment usually focuses on the execution of locomotion tasks, and is mostly based on kinematic-related measures. Typical drawbacks of marker-based motion capture systems, gold standard for measure of human limb motion, become challenging when measuring limb kinematics, due to the concomitant presence of the robot. This work answers the question of how to reliably assess the subject's body motion by placing markers over the exoskeleton. Focusing on the ankle joint, the proposed methodology showed that it is possible to reconstruct the trajectory of the subject's joint by placing markers on the exoskeleton, although foot flexibility during walking can impact the reconstruction accuracy. More experiments are needed to confirm this hypothesis, and more subjects and walking conditions are needed to better characterize the errors of the proposed methodology, although our results are promising, indicating small errors.

Modular control of gait after incomplete spinal cord injury: differences between sides

STUDY DESIGN

This is an analytical descriptive study.

OBJECTIVES

The main goal of this study was to compare the modular organization of bilateral lower limb control in incomplete spinal cord injury (iSCI) patients during overground walking, using muscle synergies analysis. The secondary goal was to determine whether the similarity between the patients and control group correlate with clinical indicators of walking performance.

SETTING

This study was conducted in National Hospital for Spinal Cord Injury (Toledo, Spain).

METHODS

Eight iSCI patients and eight healthy subjects completed 10 walking trials at matched speed. For each trial, three-dimensional motion analysis and surface electromyography (sEMG) analysis of seven leg muscles from both limbs were performed. Muscle synergies were extracted from sEMG signals using a non-negative matrix factorization algorithm. The optimal number of synergies has been defined as the minimum number needed to obtain variability accounted for (VAF) ⩾90%.

RESULTS

When compared with healthy references, iSCI patients showed fewer muscle synergies in the most affected side and, in both sides, significant differences in the composition of synergy 2. The degree of similarity of these variables with the healthy reference, together with the composition of synergy 3 of the most affected side, presented significant correlations (P<0.05) with walking performance.

CONCLUSION

The analysis of muscle synergies shows potential to detect differences between the two sides in patients with iSCI. Specifically, the VAF may constitute a new neurophysiological metric to assess and monitor patients' condition throughout the gait recovery process.

Impact of specific symptoms of spasticity on voluntary lower limb muscle function, gait and daily activities during subacute and chronic spinal cord injury

BACKGROUND

Although the spasticity syndrome is an important sensorimotor disorder, the impact of grade of lower limb muscle hypertonia, spasm and clonus activity on voluntary muscle function, gait and daily activities has not been systematically analysed during subacute and chronic spinal cord injury (SCI).

OBJECTIVE

To determine the prevalence of spasticity signs and symptoms during SCI, and to assess their impact on motor function and activities.

METHODS

A descriptive transverse study of sixty-six subjects with SCI was performed by assessing injury characteristics, spasticity (modified Ashworth scale, Penn scale, SCATS scale) and motor function (lower limb manual muscle scores, WISCI II, spinal cord injury spasticity evaluation tool).

RESULTS

Most subjects with the spasticity syndrome presented lower limb hypertonia and spasms during both subacute and chronic SCI, interfering with daily life activities. Subjects with incomplete SCI and hypertonia revealed a loss of voluntary flexor muscle activity, while extensors spasms contributed strongly to loss of gait function. The Penn spasms scale no correlated with muscle function or gait.

CONCLUSIONS

Specific diagnosis of spasm activity during subacute SCI, and its impact on lower limb voluntary muscle activity, gait function and daily activities, is required to develop a more effective neurorehabilitation treatment strategy.

A novel FES control paradigm based on muscle synergies for postural rehabilitation therapy with hybrid exoskeletons

Hybrid exoskeletons combine robotic orthoses and motor neuroprosthetic devices to compensate for motor disabilities and assist rehabilitation. The basic idea is to take benefits from the strength of each technology, primarily the power of robotic actuators and the clinical advantages of using patient's muscles, while compensating for the respective weaknesses: weight and autonomy for the former, fatigue and stability for the latter. While a wide repertory of solutions have been proposed in literature for the control of robotic orthoses and simple motor neuroprosthesis, the same problem on a complex hybrid architecture, involving a wide number of muscles distributed on multiple articulations, still waits for a practical solution. In this article we present a general algorithm for the control of the neuroprosthesis in the execution of functional coordinated movements. The method extracts muscle synergies as a mean to diagnose residual neuromotor capabilities, and adapts the rehabilitation exercise to patient requirements in a dynamic way. Fatigue effects and unexpected perturbations are compensated by monitoring functional state variables estimated from sensors in the robot. The proposed concept is applied to a case-study scenario, in which a postural balance rehabilitation therapy is presented.

Principles of human locomotion: a review

In this article the principles of human locomotion are revisited and reviewed. This has been done in the framework of two European projects, where the elicitation of these mechanisms inform, on the one hand, the design of artificial bipedal walkers (H2R), and on the other hand the design of lower limb exoskeletons (BETTER) for rehabilitation of gait in post-stroke patients. Passive dynamics emerging from the morphology of the human musculoskeletal system, reflexes as stabilization mechanisms, modular control of movement as well as supra-spinal control of gait are reviewed to get insight on how these mechanisms can be used to explain human locomotion.

Modular control of mediolateral postural sway

Is voluntary motor control of mediolateral rhythmic sway ruled by modular organization? Answering this question has potential implications in diagnosis and rehabilitation of neurologically impairments. Superficial EMG and computerized dynamic posturography has been used in this study to investigate modular control of six healthy subjects. Postural movements have been performed at three different frequencies to also test the influence of speed on the composition of synergies and activations. Results showed that two synergies account for more than 75% of EMG variance and are shared by all subjects across all frequency conditions. These evidences, together with a functional interpretation of computed muscle synergies, support the existence of consistent modular control across healthy subjects during mediolateral voluntary movements.