Increased arterial desaturation in trained cyclists during maximal exercise at 580 m altitude

This study utilized a hypobaric chamber to compare the effects of mild hypobaria (MH; 50 mmHg, similar to 580 m altitude) on blood O-2 status and maximal O-2 consumption (Vover dotO(2max)) in 9 untrained and 11 trained (T) cyclists with Vover dotO(2max) values of 51 +/- 3 and 77 +/- 1 ml . kg(-1). min(-1), respectively. In both groups, arterial O-2 saturation (Sa(O2)) decreased significantly during maximal exercise, and this effect was enhanced with MH. Both these responses were significantly greater in the T cyclists in whom the final Sa(O2) during MH was 86.5 +/- 0.9%. When the group data were combined, similar to 65% of the variance in Sa(O2) could be attributed to a widened alveolar-arterial PO2 difference. The arterial PO2 during maximal exercise at sea level in the T group was on the steeper portion of the hemoglobin-O-2-loading curve (T, 68.3 +/- 1.3 Torr; untrained, 89.0 +/- 2.9 Torr) such that a similar decrease in arterial. PO2 in the two groups in response to MH resulted in a significantly greater fall in both Sa(O2) and calculated O-2 content in the T group. As a consequence, the Vover dotO(2max) fell significantly only in the T group (mean change, -6.8 +/- 1.5%; range, +1.2 to -12.3%), with similar to 70% of this decrease being due to a fall in O-2 content. This is the lowest altitude reported to decrease Vover dotO(2max) suggesting that T athletes are more susceptible to a fall in inspired PO2.