Children with neuromuscular diseases (NMDs) and weak chest muscles suffer frequent chest infections, hospital admissions and reduced life expectancy. Physiotherapy is widely used but there is limited research data to support choice of therapy. The investigators will study the clinical value of the three most commonly used chest physiotherapy devices in children with NMD's by measuring lung function tests before and after each of the three treatments. This is a pilot study. The best device will be selected for a long term study of early physiotherapy intervention in children with NMDs.