An air vest for supplying successive percussive forces to a patient during a therapy session is described. The air vest includes an air bladder and at least one belt for securing the vest to a patient, with the vest adapted to engage at least a portion of the thoracic region of the patient. The vest may define an inner surface, an outer surface, and one or more extension portions for controlling movement of the inner and outer surfaces relative to each other along at least a portion of the vest. Securement and fitting of the vest to the patient may be achieved with a plurality of releasable straps.