Individuals with compromised ventilatory function rely on the vital skeletal muscles of respiration to adapt to changing functional demands of daily life. This dependency includes sustaining the metabolic needs of the body while at rest and during physical or emotional exertion or both. Physical therapists gain insight into the functional status of ventilatory muscles from a combination of resources that include but are not limited to inspection, palpation, circumferential chest expansion measurements, EMG, basic spirometry, pulmonary function tests, chest radiographs, and manual muscle testing of ventilatory accessory muscles. During the assessment of ventilatory muscle performance, one of the first quantitative questions to ask is if these muscles have the ability to generate enough tension to provide adequate ventilatory pressures (inspiration and expiration). For example, diaphragmatic fatigue is identified by changes in the high to low frequency ratios (H:L) on the EMG.…