General study design. After enrolment from the NMD clinic, children will be studied in batches of 15. Each batch will be studied over three consecutive weekdays so they can all receive the three treatments. On each of the study days, the group of fifteen will be randomized in groups of five to receive one of the three physiotherapy treatments. Each participant will receive all treatments at the end of the study and subsequently are considered one group. Randomization removes the chance of seeing an effect that may be due to a combination and not an individual treatment. Before and after each of the treatments, lung function tests will be measured by study staff blinded to the type of treatment. The respiratory function tests made before and after each treatment will be the same for each of the devices. By the end of the study period for that batch, every child will have completed three treatments.