Study of motor coordination for functional assessment in clinical and neurophysiological applications

Abstract

This PhD project was focused on the study of motor coordination for the purposes of functional evaluation in the clinical and neurophysiological fields. Neurological diseases, as well as being a personal problem, are also a social issue because of their high incidence, in terms of cost, on the national health system and on the employment sphere. The study of postural and motor alteration in patients with pathologies associated with movement alterations allows to know the level of functional limitation consequent to the pathology and its evolution through time, and can provide useful elements to define an appropriate rehabilitative strategy. Since walking disorders are one of the first symptoms of these patients, gait analysis, which allows evaluating kinematics, dynamics and muscle activity, provides very important information in this context. It has been shown that the breakdown of the functional balance between the various circuits is the cause of extrapyramidal motor disorders. Furthermore. a progressive loss of muscle coordination has been found in diseases affected by a deficit in the cerebellum, which therefore makes it difficult to perform voluntary movements. Injuries at the level of the pyramidal system, on the other hand, result in a progressive spasticity in the lower limbs. In this scenario, a complete characterization of the locomotion of subjects affected by several neurological diseases could be a useful tool for identifying the motor strategies put in place in order to guarantee stability and ensure progression. Among the different aspects which are the object of debate in the scientific community on gait analysis in pathologic conditions, two main questions were deepened within this PhD:  the assessment of gait patterns in patients with several neurological gait disorders (Hereditary spastic paraparesis, Parkinson's disease, cerebellar Atassia and Duchenne Muscular Dystrophy) and lower limb amputations. Some specific biomechanical features, that may not emerge because they are hidden within the global walking strategy, were highlighted by subgroups or cluster analysis.  the assessements of the role of muscle coactivation mechanisms during walking in pathologic conditions and its relstionship with gait performance. The influence of several factors in the sEMG measurement and pre-processing on the linear envelope profiles extraction, and therefore on the outcome of muscle co-activation were taken into account. Firstly, starting from a review of literature, I addressed my attention to a kinematic, kinetic, energetic and electromyographic characterization of the path of the aforementioned subjects with the aim of identifying the motor strategies to ensure stability and coordination during movement. As regard patients with Hereditary Spastic Paraparesis (HSP), several previous studies highlighted the clinical variability and heterogeneity of the pathology. In addition to general biomechanical characteristics of gait, one would expect some differential characteristics in distinct subgroups of patients according to clinical involvement of the pyramidal tract, given that patients with HSP exhibit different degrees of severity both within and between families. The analysis of limb joint kinematics revealed that, when subgrouping patients according to the hip, knee and ankle joint kinematic behavior, three clear gait patterns emerged HPS patients. Thus, the identification of several walking strategies among HSP patients provide useful elements to define an appropriate rehabilitative strategy. The progression of gait impairment in a group of patients with primary degenerative cerebellar ataxias (CA) over a period of 4 years revealed a progressive increase in gait variability which may directly reflect gait function deterioration. Interestingly, the increase in trunk rotation may represent a compensatory mechanism aimed at maintaining an adequate gait speed. As regard patients affected by Duchenne Muscular Dystrophy (DMD), the progressive increase in gait variability observed at the 2-year follow-up may thus directly reflect a deterioration of the gait function, which leads to greater instability. Taking this into consideration, gait variability seems to anticipate the future loss of walking autonomy. The analysis of the trunk movement suggested that the abnormal trunk movement in neurological patients reflect either a primary deficit or a compensatory mechanism. Particularly, the trunk may be used as generator of movement to improve gait performance in some patients (e.g. in HSP) but not in other (e.g. in Parkinson's disease). Patients with whole body deficits may use trunk movement either as a perturbator, increasing its range of motion, either as a damper, decreasing its range of motion. Finally, in spite of common gait characteristics in subjects with lower limb prostheses, both the anatomical level of amputation and type of prostheses determine a specific gait pattern that should be taken into account when developing new and ergonomic prosthetic devices and when planning the rehabilitation programs aimed at improving the physiology of gait and reducing the gait asymmetries. Afterwards, I followed a methodological approach with the aim of identifying robust indices to characterize pathologic conditions. Specifically, the mechanism of muscle co-activation, which is important for providing adequate spine and joint stability, energy efficiency and for adapting to environmental demands, was investigated focusing on the influence of sEMG processing technique (such as the extraction of linear envelopes or signal to noise condition) on the outcome of muscle co-activation. The analysis of the results shows that the performance of the methodologies used to assess muscle co-activation are influenced by the choice of the low pass cut-off frequency, as well as by the level of signal to noise ratio. Thus, since the relevance of the analysis of muscle co activation to several fields is well known, it is important to correctly process myoelectric signals in order to extract this parameter by avoiding estimation bias. During walking, muscle joint coactivation varies within the gait cycle according to the functional role of the lower limb joints. Our results show that muscle coactivation in healthy subjects is speed dependent and positively correlated with both energy consumption and balance related gait parameters. The investigation of the lower limb muscle coactivation in patients with HSP showed that the abnormal coactivation pattern may reflect both or either abnormal descending motor commands and/or plastic rearrangement of the spinal circuitries which, in turn, lead to a lack of selectivity of the descending motor drives to motoneuronal pools. In addition, these abnormalities influence the mechanisms of both energetic consumption and recovery during walking. Furthermore, in patients with DMD, since gait speed remained approximately unchanged over time, increased muscle co-activation at proximal level represents the most important strategy to compensate for a deterioration in both functional ability and increase in gait instability. The results highlight the importance of a methodological approach for testing the role of muscle co-activation mechanism during the execution of motor tasks avoiding possible bias due to sEMG processing techniques. Muscle coactivation in patients could be a useful measure of the motor control strategy, limb stiffness, postural stability, energy efficiency optimization, and several aspects in pathological conditions. In conclusion, the results obtained in this PhD project may provide important support to extend the knowledge about functional assessment in clinical and neurophysiological fields. In particular, these results suggested that both the characteristics of the pathology and the technique used for data elaboration are two important aspects to be considered in the design of tools for training and rehabilitation.