Maximal inspiratory pressure following endurance training at altitude

Effects of endurance training on maximal inspiratory pressure and fatigue were evaluated after 5 weeks. Twelve male and 9 female untrained subjects were matched in the three groups for sex and maximal oxygen uptake (VO₂max). Training was performed at 70% VO₂ max; 45min day⁻¹;5 days week⁻¹ (n = 7); and at the same relative (n = 7) and absolute (n = 7) work loads in a pressure chamber corresponding to 2500m(560 mmHg). Work load was increased every week to maintain the training heart rate. Maximal inspiratory pressure was measured at the mouth before and 30, 60 and 120s after maximal exercise. With no significant difference between the three groups of subjects, VO₂max increased from 2.96 (1.98-4.47) (median and range for 21 subjects) to 3.33 (2.50-4.72)1 min⁻¹(<0.001) and ventilation (VEmax) from 109 (57-147) to 123 (73-148)1 min⁻¹ (p< 0.001), while maximal heart rate decreased from 193 (180-211) to 192 (169-207) beats min⁻¹(p < 0.01). Maximal inspiratory pressure (87 (56-115) mmHg), inspiratory muscle fatigue (18 (- 2-43)%, p < 0.001), and arterial oxygen tension during exercise (12.4 (9.9-15.6) kPa) were similar before and after training. The results demonstrate that training at simulated altitude at 2500 m does not increase VEmax or VO₂max above the increases obtained from training at sea level. Furthermore, VEmax and VO₂max increased approximately 13% despite unchanged maximal inspiratory pressure and inspiratory muscle fatigue. These findings indicate that inspiratory muscles do not limit maximal performance of short duration in untrained humans.