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

Gore, C.J., Hahn, A.G., Scroop, G.S., Watson, D.B., Norton, K.I., Wood, R.J., Campbell, D.P., Emonson, D. L. 'Increased arterial desaturation in trained cyclists during maximal exercise at 580m altitude', Journal of Applied Physiology, 80(6): 2204-2210, 1996.

This study utilized a hypobaric chamber to compare the effects of mild hypobaria (MH; 50 mmHg, approximately 580 m altitude) on blood O₂ status and maximal O₂ consumption (VO_2max) in 9 untrained and 11 trained (T) cyclists with VO_2max values of 51 +/- 3 and 77 +/- 1 ml.kg^-1.min^-1, respectively. In both groups, arterial O₂ saturation (S_aO₂) 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 S_aO₂ during MH was 86.5 +/- 0.9%. When the group data were combined, approximately 65% of the variance in S_aO₂ 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-O₂-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 S_aO₂ and calculated O₂ content in the T group. As a consequence, the VO_2max fell significantly only in the T group (mean change, -6.8 +/- 1.5%; range, + 1.2 to - 12.3%), with approximately 70% of this decrease being due to a fall in O₂ content. This is the lowest altitude reported to decrease VO_2max, suggesting that T athletes are more susceptible to a fall in inspired PO₂.