It is very important monitoring respiratory muscle function in patients with amyotrophic lateral sclerosis (ALS). We have at our disposal Respiratory Functional Tests (forced vital capacity (FVC), maximal mouth-inspiratory force (MIF), maximal mouth-expiratory force (MEF), Cough Peak expiratory flow (cPEF), maximal voluntary ventilation (MVV), arterial blood gases and nocturnal pulsioxymetry) and Thoracic Image Techniques (inspiratory/expiratory Thorax x-ray and x-ray scope). But all this explorations present some technique limitations. They are two new methods to explore diaphragmatic function: SNIF test and Diaphragm magnetic resonance imaging (dMRI). SNIF test is simple and easy to be done and it can avoid some problems that have the other respiratory functional test in this kind of patients. dMRI seems to correlate with respiratory functional test and it can be useful monitoring diaphragmatic mobility. The objective of our study is to compare and to correlate SNIF test and dMRI with x-ray techniques and respiratory functional tests that measure diaphragmatic force and function. First of all we will study 10 healthy people with a forced spirometry, MIF, MEF and dMRI, trying to obtain diaphragmatic mobility reference values with dMRI. Lately, we will study patients with ALS. In the first place, we will perform a transversal study with 30 patients. We will do a forced spirometry, MIF, MEF, MVV, cPEF, SNIF, arterial blood gases and nocturnal pulsioxymetry, forced Inspiratory and expiratory Thorax x-ray, diaphragmatic x-ray scope and dMRI. Secondly, we will perform a prospective study, where we will analyze these variables evolution at 3 and 6 months. We hope we can apply the two new techniques in the future because we think they are simpler, more accurate and more objective to evaluate diaphragmatic mobility.