Effects of physical exercise on neuromuscular performance and quality of life in people with multiple sclerosis

Resumen

Sedentary lifestyle is one of the main problems facing the population today. Low levels of physical activity have been correlated with an increased risk of various diseases, resulting in increased mortality and morbidity rates. Considering this fact, home confinement caused by the COVID-19 pandemic, which forced the general population to become housebound for almost nine weeks, made it more difficult for the population to maintain their usual physical activity levels, specifically in vulnerable populations such as patients with multiple sclerosis. This supervening situation prompted the need to study the effects of confinement on the signs and symptoms associated with multiple sclerosis. On the other hand, previous research has demonstrated, since the 1980s, the potential of physical exercise may have on people with multiple sclerosis. Thus, different types of exercise, mainly aerobic and strength training programs, have been established as valid strategies to improve muscle strength, functional capacity or mobility. However, the effect of these types of training or the optimal dose of exercise to improve neuromuscular performance variables, functional capacity or quality of life are still unknown. In this context, it is also unknown how the manipulation of some of the training variables, such as the intention to move the load at maximum velocity in strength training, influences neuromuscular and quality of life variables in people with multiple sclerosis. Thus, it is necessary to control the estimation of intensity in strength training, another variable that determines neuromuscular adaptations. The control of intensity in strength exercise is carried out through a wide variety of methods, among which the repetition maximum is the most widespread. However, its direct calculation has several disadvantages, such as the long time required or the high fatigue it causes, problems that in people with multiple sclerosis may acquire, and possible with more magnitude. For this reason, in this population, it is necessary to validate other indirect methods for calculating the maximum repetition, such as the one based on movement velocity. On the other hand, in recent years, there has been growing interest in other types of alternative training, among which whole-body vibration training stands out. This type of training has lower perceptions of fatigue and provides long-term neuromuscular benefits, making it an interesting exercise modality for people with multiple sclerosis. However, the acute effects of this training in this population have not been studied. In addition, and in search of training that leads to the greatest benefits with the least fatigue, the use of the hypoxia condition presents itself as a potentially interesting tool. Therefore, the combination of vibration training and hypoxia condition could be effective in a chronic way, but its effects in an acute way should be studied first. Therefore, the present doctoral thesis was proposed with the general objective of analyzing the effect of confinement, as well as the acute effects and adaptations to different types of physical exercise programs on neuromuscular performance and quality of life in the population with multiple sclerosis. Firstly, the three studies carried out during the COVID-19 pandemic are presented, in which the consequences of home confinement on some of the main signs and symptoms of the disease in the population with multiple sclerosis were examined. Furthermore, the doctoral thesis includes two meta-analyses that analyze the effects and optimal dose of aerobic training and strength training on neuromuscular variables, functional capacity and quality of life in people with multiple sclerosis. In addition, the acute effects of vibration training in normoxic and hypoxic conditions on neuromuscular, physiological and functional performance were examined in a sample of persons with multiple sclerosis. Also, a study was implemented to validate movement velocity as a method for estimating maximal repetition in this population. Finally, another five studies were carried out to analyze the effects of 10 weeks of strength training developing the concentric phase of movement at maximum voluntary velocity on different neuromuscular, functional, cardiac autonomic control and quality of life parameters in a population with multiple sclerosis. The results showed that nine weeks of home confinement resulted in worsened sleep quality, functional capacity, anxiety, general physical selfperception, voluntary activation, and spasticity in participants with multiple sclerosis. However, muscle contractile properties, muscle activity during a maximal contraction, maximal strength, self-perceived quality of life, and cardiac autonomic control were not modified after the confinement period in the sample of persons with multiple sclerosis. From a meta-analytic point of view, aerobic training programs led to improvements in cardiorespiratory fitness, functional capacity, balance and fatigue perception, whereas strength training programs led to improvements in maximal isometric strength, functional capacity and balance. The results regarding the optimal dose were inconclusive. On the other hand, the study of the acute effects of vibration training under hypoxia and normoxia showed no differences between conditions after the training session in voluntary activation, maximal isometric strength, functional capacity or balance. However, decreases in muscle activity were found after the hypoxia session compared to the normoxia session. Regarding the validation of movement velocity as a method to estimate intensity, a linear relationship was found between the direct method of calculating the repetition maximum and the estimation of the repetition maximum through movement velocity in leg press and bench press exercises in the population with multiple sclerosis. Finally, strength training performed with the concentric phase at maximum velocity caused improvements in maximal strength, rate of force development, voluntary activation, neural drive, functional capacity, spasticity, self-perceived quality of life, sleep quality and perception of fatigue and pain in people with multiple sclerosis. However, this training modality did not lead to improvements in cardiac autonomic control, muscle contractile properties or static balance. In conclusion, the results of the present thesis highlight the negative effects of confinement on some of the main signs and symptoms of multiple sclerosis. Furthermore, it highlights the usefulness of physical exercise, mainly aerobic and strength training, for the improvement of neuromuscular performance and quality of life in people suffering from this neurological disease. Also, it is shown that vibratory training in hypoxia condition, acutely, is a safe training mode in this population. In addition, it was proved that the movement velocity is a valid method to estimate the intensity in strength exercises in people with multiple sclerosis. Finally, it is shown that strength training performed with the concentric phase at maximum voluntary velocity is a type of training that provides interesting benefits, mainly neuromuscular and functional, in this population