The principal question in the management of children with NMDs is whether early introduction of effective respiratory therapy will slow the decline in lung function and help to keep these children out of hospital. That requires long term studies of the use of therapies known to be effective, at least in the short term. Such evidence - even short term evidence of efficacy, is not available. Our study is not a case of comparing a new treatment to an established therapy, it is a case of assessing current widely used treatments in order to determine whether they have any measurable benefits. The best of the three techniques studied will then form the basis for a long term early intervention study.