Fatigue is a complex physiological phenomenon by which the individual's ability to maintain a particular physical activity is limited (Bigland-Ritchie and Woods, 1984). In healthy individuals the development of fatigue is linked to physical exercise being the main cause that limits the duration of the same. In addition, fatigue appears as part of the pathology of different diseases and its effect is also limiting of physical activity. The study of such a complex phenomenon has been carried out with different experimental approaches and at different physiological levels with healthy individuals, which has allowed to distinguish three basic types of fatigue: a) peripheral fatigue, produced in the neuro-muscular system, b) fatigue systemic response produced by the neuro-endocrine response, c) central fatigue occurring in the central nervous system (Taylor and Gandevia, 2008; Zwartz et al, 2008). A medullary lesion (LM) is damage to the central nervous system (CNS), both motor and regulatory pathways of movement, sensory or ascending pathways, and major circuits of the autonomic nervous system. The alteration of these structures in the medium and long term generates physiological modifications in both the sensoriomotor cerebral cortex (neuropathic pain, phantom limb, etc.) and in the spinal cord (spasticity, hyperreflexia, neuropathic pain, sympathetic hyperreflexia, etc.). People with LM (PLM) suffer from general fatigue (Fawkes-Kirby et al 2007, Anton et al 2008) associated with their disease. Therefore, a LM should modify the development and / or intensity of central fatigue, which has not been studied until today. Possible causes of excessive central fatigue in the injured spinal cord may be of nervous origin but also of systemic origin. The dysautonomy of the injured medullary patients can cause an alteration of the systemic homeostatic mechanisms of temperature, electrolytes, etc. and thus produce excessive central fatigue also above the level of injury. Thus, a comparative study of central fatigue in healthy individuals and in individuals with spinal cord injury (at the supralateral level) could provide insight into the general problem of central fatigue and, in particular, the central changes that spinal cord injury causes in the people. In this sense, the use of non-invasive techniques for CNS stimulation and recording has allowed to advance in the study of central fatigue (Di Lazzaro, Oliviero et al 2003, Racinais et al 2007). These new techniques, together with the classic surface electromyography, allow, especially in the cerebral cortex and in the spinal cord, to evaluate the involvement of the CNS in the development of fatigue to help generate knowledge about how the disease can affect the quality of movement. Based on the theoretical framework we studied, the initial hypothesis that was established was that the behavior of the mechanisms of development of central fatigue in people with LM would be different from those developed by healthy people without pathologies during acute tasks. As a secondary hypothesis, it was pointed out that for the same task proposed, peripherally measured fatigue in people with LM would present similar or even lower values than people without injury. In order to answer the hypotheses, the main objective of the thesis was to describe the influence that fatigue has on the quality of movement of PLM through the study of the mechanisms of development of central and peripheral fatigue during CMV in people with LM in relation to their behavior in people without disability (CG) and the secondary objective was to establish objective criteria that quantify and describe the mechanisms of development of central and peripheral fatigue in the population with LM through the NS study. In this sense and after carrying out the experimental phase of this Doctoral Thesis, the analysis of results and their subsequent discussion, both hypotheses are confirmed, fulfilling both the main and secondary objectives. The conclusions reached after the discussion of results are: • Fatigue does not appear to have any negative influence on PLM movement quality through the study of the mechanisms of central and peripheral fatigue during CMV in people with LM versus their behavior in people without disabilities (GC). • PLMs present less fatigue, both centrally and peripherally, compared to the CG, and even the central fatigue that the PLMs present after the effort is significantly lower than that manifested by the CG. • However, the development mechanisms of both cortical and peripheral fatigue are different in PLM compared to control group.
2017-09-07
