Methods and Systems for the Biomechanical Characterization of the Upper Limb

Human movement is the main objective of study of biomechanics. It can be analyzed from the perspective of its kinematic, kinetic, electomyographic and anthropometric characteristics. The human upper limbs and, in particular, the human hand, are the most fascinating and challenging body districts to study, as they enable the execution of precise and dexterous movements. Given the extreme complexity of the human hand, it is essential to develop methods and systems to comprehensively model and study the characteristics of these districts. Moreover, the occurrence of diseases affecting the upper limbs, including hand amputations, can significantly decrease patients autonomy and reduce the quality of life. If follows that it is paramount to design efficient and effective devices that can compensate the loss of functionality and to objectively evaluate the performance of these districts during rehabilitative treatments. Accurate protocols capable of reconstructing all degrees of freedom of the hand are required to characterize hand kinematics. The determination of the hand fingers centers of rotation could contribute to the further improvement of such protocols. However, the methods identified in the literature for determining such centers are often computationally non-trivial and use a very large number of markers. Furthermore, the analysis of the literature has highlighted limits in relation to the study of the fundamental hand movement strategies, i.e., intra-finger couplings and motor synergies. In fact, intra-finger couplings were only studied in relation to the execution of grasping tasks, i.e., constrained movements, and despite the task-specificity of synergies was hypothesized in previous studies, no works have extracted synergies on specific grasp classes to identify distinctive movement patterns. Moreover, the possible relations between the different variables involved in the grasping action (i.e., multidomain synergies including kinematic, force and muscular information) has not been analyzed yet. The outputs obtained by the hand kinematic analysis, including the definition of hand movement strategies, could provide important input design parameters for the development of biomimetic assistive devices. To date, the evaluation of the hand functionality, which is paramount to objectively assess improvements of patients throughout the rehabilitation process, is mainly based on time parameters measured during the execution of the grasping task. However, several other indicators based on hand posture, movement speed and grasping force should be included in the evaluation of hand functionality, and a lack of tools that allow automatically calculating such indicators was identified in the literature. This thesis deals with the biomechanical characterization of the human hand and upper limb from a kinematic, kinetic and electromyographic perspective, with a twofold objective: i) to provide methods and systems for the objective assessment of the hand functionality and ii) to extract input design parameters that can guide the development of biomimetic prostheses and orthoses. The kinematics of the human hand was extensively studied by exploiting an optimized kinematic reconstruction protocol which allows reconstructing joint angles from marker positions recorded with an optoelectronic motion capture system. In the context of extracting input design parameters for developing prosthetic and exoskeletal assistive devices, the kinematic protocol was applied to estimate joint intra-finger couplings and kinematic synergies, as well as hand joints centers of rotation. Moreover, the protocol was exploited to objectively assess hand functionality and a toolbox for automatic hand clinical assessment was developed. The knowledge of the kinematic characteristics of the upper limb also allowed defining a protocol for the functional validation of M-IMUs, that could be used as a good alternative to optoelectronic systems to reconstruct upper limb kinematics. The human hand was also characterized from a kinetic and electromyographic perspective. Forces exerted by the hand and muscular activation during the execution of grasping tasks were analyzed in combination with kinematic parameters with the aim of identifying shared strategies among healthy volunteers, that could inspire the development of optimized hand prostheses. In the framework of objectively evaluating hand functionality, a system for the assessment and recovery of grip force control was proposed and used to assess grip performance in patients with neurological and musculoskeletal disorders.