Lomax M. Inspiratory muscle training, altitude, and arterial oxygen desaturation: a preliminary investigation. Aviat Space Environ Med 2010; 81:498–501. Introduction: Specific inspiratory muscle training (IMT) has been shown to significantly attenuate the fall in arterial oxygen saturation (S_po₂) during exhaustive exercise while breathing a hypoxic gas mixture of 14% oxygen. The aim of the current study was to assess the impact of IMT on resting S_po₂ over a range of altitudes in healthy individuals. Methods: Resting S_po₂ and the Borg Score were examined at altitudes of 0 or 400 m (0–400 m; 0–1312.3 ft), 1400 m, 4880 m, and 5550 m (4593 ft, 16,011 ft, and 18,209 ft) in 14 military personnel who were part of a climbing expedition to the Nepali Himalaya. Volunteer participants were randomly assigned to either a control (N = 7) or IMT (N = 7) group: IMT consisted of 1 set of 30 breaths twice daily at 50% maximal inspiratory mouth pressure (MIP) for 4 wk prior to departure. Results: MIP was similar between groups pre-IMT but increased significantly by 15% post-IMT. Baseline maximal expiratory mouth pressure was not different between groups. The Borg Score increased significantly from 1400 m, but was not different between groups at any altitude. Resting S_po₂ declined significantly at ascending altitudes in both groups and was similar between groups at altitudes of 0-400 m and 1400 m. However, at altitudes of 4880 m and 5550 m, S_po₂ was significantly higher (6%) in the IMT group. Conclusion: IMT can attenuate the fall in resting S_po₂, but only at altitudes of 4880 m and above. Conversely, IMT had no effect on resting levels of dyspnea as measured by the Borg Score.