Exoskeletons for lower and upper extremities have been introduced in neurorehabilitation because they can guide the patient’s limb following its anatomy, covering many degrees of freedom and most of its natural workspace, and allowing the control of the articular joints. The aims of this study were to evaluate the possible use of a novel exoskeleton, the Arm Light Exoskeleton (ALEx), for robot-aided neurorehabilitation and to investigate the effects of some rehabilitative strategies adopted in robot-assisted training.
We studied movement execution and muscle activities of 16 upper limb muscles in six healthy subjects, focusing on end-effector and joint kinematics, muscle synergies, and spinal maps. The subjects performed three dimensional point-to-point reaching movements, without and with the exoskeleton in different assistive modalities and control strategies.
The results showed that ALEx supported the upper limb in all modalities and control strategies: it reduced the muscular activity of the shoulder’s abductors and it increased the activity of the elbow flexors. The different assistive modalities favored kinematics and muscle coordination similar to natural movements, but the muscle activity during the movements assisted by the exoskeleton was reduced with respect to the movements actively performed by the subjects. Moreover, natural trajectories recorded from the movements actively performed by the subjects seemed to promote an activity of muscles and spinal circuitries more similar to the natural one.
The preliminary analysis on healthy subjects supported the use of ALEx for post-stroke upper limb robotic assisted rehabilitation, and it provided clues on the effects of different rehabilitative strategies on movement and muscle coordination.
In 2010, 8.2 million of people in Europe were affected by a stroke, with a total cost of about 64 billion euro per year . With the increasing of life duration, it is expected that the stroke related disabilities in western societies would be ranked to the fourth most important causes of disability in 2030 . Impairments in reaching movements occur in about two-thirds of stroke survivors: upper limb functions are altered in the 73–88 % of first time stroke survivors, and in the 55–75 % of chronic post-stroke patients [3, 4]. Indeed, in most of the cases post-stroke subjects remain unable to use their paretic limb to execute even basic actions, losing their independence in carrying out the everyday activities.
Rehabilitation has the ultimate outcome to reintroduce the patient as an active participating member in the society . Rehabilitative interventions based on task-oriented repetitive movements have showed to improve muscle strength and movement coordination in patients with neurological impairments [6, 7], pointing out how intensive rehabilitation can have long-term benefits in patients with moderate-to-severe impairment, even years after a stroke . For the above reasons, in the last decades, robotic-based rehabilitation, which allows improving the intensity and the repeatability of the rehabilitative treatment, has become very widespread. Indeed, robots can both provide quantitative measures of motor performances for the assessment of motor improvement  and precisely control the execution of complex motor tasks , producing measured levels of assistance or precise repeatable force patterns , and allowing the design of rehabilitative interventions that continuously challenge the patient’s neuromuscular system …