Restitution and compensation in the recovery of function in the lower extremities of stroke survivors : design of evaluation and training methods

Since restoration of motor function in walking and stance is an important aspect in the rehabilitation of stroke patients, insight in the responsible recovery mechanisms is of great importance. Generally, two recovery mechanisms are distinguished: restitution and compensation. In restitution, the increase in motor function is attributed to a return of original movements and or function of the paretic leg, whereas in compensation the increase in motor function is ascribed to the emergence of new movement strategies or to secondary adaptations in the non paretic leg to compensate for the decreased motor abilities in the paretic leg. To assess the contribution of the different mechanisms in the recovery of motor function, we need to develop appropriate methods to quantify restitution and compensation in time. Besides, the contributions of the separate recovery mechanisms can also be derived from the effectiveness of therapeutic interventions that focus specifically on using original movement patterns (restitution) or alternative movement strategies (compensation). Robotic rehabilitation devices can well be used in emphasizing the use of certain movement strategies during training, as they can support the movements of the subject during practicing. However, practicing compensatory\ud strategies in the device is only possible if the mechanical design of the device allows for it and if the control of the device provides the flexibility to the subjects in choosing their movement strategy. The latter requires the implementation of “assist-as-needed” algorithms that only provide assistance to the subject when it is needed to successfully fulfill the task

Use of induced acceleration to quantify the (de)stabilization effect of external and internal forces on postural responses

Due to the mechanical coupling between the body segments, it is impossible to see with the naked eye the causes of body movements and understand the interaction between movements of different body parts. The goal of this paper is to investigate the use of induced acceleration analysis to reveal the causes of body movements. We derive the analytical equations to calculate induced accelerations and evaluate its potential to study human postural responses to support-surface translations. We measured the kinematic and kinetic responses of a subject to sudden forward and backward translations of a moving platform. The kinematic and kinetics served as input to the induced acceleration analyses. The induced accelerations showed explicitly that the platform acceleration and deceleration contributed to the destabilization and restabilization of standing balance, respectively. Furthermore, the joint torques, coriolis and centrifugal forces caused by swinging of the arms, contributed positively to stabilization of the center of mass. It is concluded that induced acceleration analyses is a valuable tool in understanding balance responses to different kinds of perturbations and may help to identify the causes of movement in different pathologies

Haptic human-human interaction does not improve individual visuomotor adaptation

Haptic interaction between two humans, for example, parents physically supporting their child while it learns to keep balance on a bicycle, likely facilitates motor skill acquisition. Haptic human-human interaction has been shown to enhance individual motor improvement in a tracking task with a visuomotor rotation perturbation. These results are remarkable given that haptically assisting or guiding an individual rarely improves their motor improvement when the assistance is removed. We, therefore, replicated a study that reported benefits of haptic interaction between humans on individual motor improvement for tracking a target in a visuomotor rotation. Also, we tested the effect of more interaction time and stronger haptic coupling between the partners on individual performance improvement in the same task. We found no benefits of haptic interaction on individual motor improvement compared to individuals who practised the task alone, independent of interaction time or interaction strength. We also found no effect of the interaction partner's skill level on individual motor improvement

Design and Evaluation of the LOPES Exoskeleton Robot for Interactive Gait Rehabilitation

This paper introduces a newly developed gait rehabilitation device. The device, called LOPES, combines a freely translatable and 2-D-actuated pelvis segment with a leg exoskeleton containing three actuated rotational joints: two at the hip and one at the knee. The joints are impedance controlled to allow bidirectional mechanical interaction between the robot and the training subject. Evaluation measurements show that the device allows both a "pa- tient-in-charge" and "robot-in-charge" mode, in which the robot is controlled either to follow or to guide a patient, respectively. Electromyography (EMG) measurements (one subject) on eight important leg muscles, show that free walking in the device strongly resembles free treadmill walking; an indication that the device can offer task-specific gait training. The possibilities and limitations to using the device as gait measurement tool are also shown at the moment position measurements are not accurate enough for inverse-dynamical gait analysis

The Existence of Shared Muscle Synergies Underlying Perturbed and Unperturbed Gait Depends on Walking Speed

Muscle synergy theory assumes that the central nervous system generates a wide range of complex motor outputs by recruiting muscle synergies with different strengths and timings. The current understanding is that a common set of muscle synergies underlies unperturbed as well as perturbed walking at self-selected speeds. However, it is not known whether this is the case for substantially slower walking. The aim of this study was to investigate whether a shared set of muscle synergies underlies balance recovery responses following inward-and outward-directed perturbations in the mediolateral direction at various perturbation onsets and walking speeds. Twelve healthy subjects walked at three walking speeds (0.4, 0.6, and 0.8 m/s) on a treadmill while perturbations were applied to the pelvis using the balance assessment robot. A set of sixteen EMG signals, i.e., eight muscles per leg, was measured and decomposed into muscle synergies and weighting curves using non-negative matrix factorization. The muscles included were left and right tibialis anterior, soleus, gastrocnemius medialis, gastrocnemius lateralis, rectus femoris, hamstring, gluteus medius, and gluteus maximus. In general, four muscle synergies were needed to adequately reconstruct the data. Muscle synergies were similar for unperturbed and perturbed walking at a high walking speed (0.8 m/s). However, the number of similar muscle synergies between perturbed and unperturbed walking was significantly lower for low walking speeds (0.4 and 0.6 m/s). These results indicate that shared muscle synergies underlying perturbed and unperturbed walking are less present during slow walking compared to fast walking