Muscle synergies and spinal maps are sensitive to the asymmetry induced by a unilateral stroke.

BACKGROUND: Previous studies have shown that a cerebrovascular accident disrupts the coordinated control of leg muscles during locomotion inducing asymmetric gait patterns. However, the ability of muscle synergies and spinal maps to reflect the redistribution of the workload between legs after the trauma has not been investigated so far. METHODS: To investigate this issue, twelve post-stroke and ten healthy participants were asked to walk on a treadmill at controlled speeds (0.5, 0.7, 0.9, 1.1 km/h), while the EMG activity of twelve leg muscles was recorded on both legs. The synergies underlying muscle activation and the estimated motoneuronal activity in the lumbosacral enlargement (L2-S2) were computed and compared between groups. RESULTS: Results showed that muscle synergies in the unaffected limb were significantly more comparable to those of the healthy control group than the ones in the affected side. Spinal maps were dissimilar between the affected and unaffected sides highlighting a significant shift of the foci of the activity toward the upper levels of the spinal cord in the unaffected leg. CONCLUSIONS: Muscle synergies and spinal maps reflect the asymmetry as a motor deficit after stroke. However, further investigations are required to support or reject the hypothesis that the altered muscular organization highlighted by muscle synergies and spinal maps may be due to the concomitant contribution of the altered information coming from the upper part of the CNS, as resulting from the stroke, and to the abnormal sensory feedback due to the neuromuscular adaptation of the patients.

Kinematic characterization of functional reach to grasp in normal and in motor disabled children.

The upper limb kinematics were assessed during the execution of a functional task in healthy adults, children and in children with motor disabilities (i.e. hemiplegic cerebral palsy (HCP) and movement disorders (MD)). The quantitative assessment was performed considering the time durations, the amplitude of movements at different joints and the periodicity of the acceleration patterns. Compared to adults, healthy children showed increased motion amplitudes both at the head and at the trunk; this is suggestive of a reduced ability to stabilize the head during reaching. Furthermore, healthy children showed a reduced periodicity of the acceleration patterns which is interpreted as an indication of the on-going maturation process of the central nervous system. Subjects with HCP and MD showed increased movement duration; however this general finding does not account for specific differences. Indeed, children with HCP showed reduced range of motion (ROM) of the shoulder on the frontal plane which is counterbalanced by the introduction of compensatory movements of the trunk. Conversely, in children with MD, the ROM is well-preserved whereas the movements of the head are increased especially at higher speed. Finally, the periodicity of the end-effect is dramatically reduced both in HCP and MD. This suggests the existence of out-of-phase corrective strokes that may indicate an increased variability of the motor control commands. The results of this study reinforce the evidence that kinematic analysis may add valuable information to understand the developmental process in healthy children and to differentiate distinct levels of impairment in children with neurological disorders.

Assessment of walking features from foot inertial sensing.

An ambulatory monitoring system is developed for the estimation of spatio-temporal gait parameters. The inertial measurement unit embedded in the system is composed of one biaxial accelerometer and one rate gyroscope, and it reconstructs the sagittal trajectory of a sensed point on the instep of the foot. A gait phase segmentation procedure is devised to determine temporal gait parameters, including stride time and relative stance; the procedure allows to define the time intervals needed for carrying an efficient implementation of the strapdown integration, which allows to estimate stride length, walking speed, and incline. The measurement accuracy of walking speed and inclines assessments is evaluated by experiments carried on adult healthy subjects walking on a motorized treadmill. Root-mean-square errors less than 0.18 km/h (speed) and 1.52% (incline) are obtained for tested speeds and inclines varying in the intervals [3, 6] km/h and [-5, + 15]%, respectively. Based on the results of these experiments, it is concluded that foot inertial sensing is a promising tool for the reliable identification of subsequent gait cycles and the accurate assessment of walking speed and incline.

Characterization of EMG patterns from proximal arm muscles during object- and orientation-specific grasps.

Reach-to-grasp tasks are composed of several actions that are more and more considered as simultaneously controlled by the central nervous system in a feedforward manner (at least for well-known activities). If this hypothesis is correct, during prehension tasks, the activity of proximal muscles (and not only of the distal ones used to control finger movements) is modulated according to the kind of object to be grasped and its position. This means that different objects could be identified by processing the electromyographic (EMG) signals recorded from proximal muscles. In this paper, specific experiments have been carried out to support this hypothesis in able-bodied subjects. The results achieved seem to confirm this possibility by showing that the activation of proximal muscles can be statistically different for different grip types. This finding supports the hypothesis that proximal and distal muscles are simultaneously controlled during reaching and grasping. Moreover, this kind of information could allow the development of an EMG-based control strategy based on the natural muscular activities selected by the central nervous system.