Measured end points. The effects of the three respiratory treatments will be assessed using standard lung function tests. A baseline will be obtained prior to each treatment. Repeat tests will be performed immediately after the treatment, then at ½, 1 and 2 hours later. Comparative predictive lung function values are based on algorithms that rely on patient height. In those children with severe spinal deformity, arm span will be used as a surrogate for height. All tests will be made by qualified respiratory technicians using regularly maintained and calibrated equipment. The staff measuring, reporting and storing the results will be blinded to the child's therapy. Other tests commonly used in the assessment of children with NMDs, such as oximetry and capnography, will not be measured since it is unlikely they will change over the short duration of the study. The following end points will be measured: lung volume, cough expiratory flows, and muscle strength.