Effect of Acute Hypoxia on Maximal Exercise in Trained and Sedentary Women XAVIER WOORONS 1 , PASCAL MOLLARD 1 , CHRISTINE LAMBERTO 2 , MURIEL LETOURNEL 3 , and JEAN-PAUL RICHALET 1 1 Laboratory of Functional and Cellular Responses to Hypoxia, Association for Research in Environmental Physiology, UFR-SMBH Universite Paris, FRANCE; 2 Avicenne Hospital, Universite Paris, FRANCE; and 3 Avicenne Hospital, Bobigny, FRANCE ABSTRACT WOORONS, X., P. MOLLARD, C. LAMBERTO, M. LETOURNEL, and J.-P. RICHALET. Effect of Acute Hypoxia on Maximal Exercise in Trained and Sedentary Women. Med. Sci. Sports Exerc., Vol. 37, No. 1, pp. 147–154, 2005. Purpose: The purpose of this study was to determine the physiological responses of sedentary and endurance-trained female subjects during maximal exercise at different levels of acute hypoxia. Methods: Fourteen women who were sea level residents were divided into two groups according to their level of fitness: 1) endurance-trained women (TW) (N = 7), V ˙ O 2max = 56.3  4.7 mL·kg -1 ·min -1 ; and 2) sedentary women (SW) (N = 7), V ˙ O 2max = 34.8  5.6 mL·kg -1 ·min -1 . Subjects performed four maximal cycle ergometer tests in normoxia and under hypoxic conditions (F I O 2 = 0.187, 0.154, and 0.117, corresponding to altitudes of 1000, 2500, and 4500 m, respectively). Results: V ˙ O 2max decreased significantly by 3.6  2.1, 14  2.5, and 27.4  3.6% in TW, and by 5  4, 9.4  6.4, and 18.7  7% in SW at 1000, 2500, and 4500 m, respectively. The drop of V ˙ O 2max (V ˙ O 2max ) was greater in TW at and above 2500 m. Arterial O 2 saturation (SpO 2 ) at maximal exercise was lower in TW at every altitude (1000 m: 90.9  1.9 vs 94.6  1.4%; 2500 m: 82.8  2.8 vs 90.0  2.1%; 4500 m: 65.0  4.7 vs 73.6  4.5%). Maximal heart rate decreased significantly from 1000 m in the two groups. SpO 2 was correlated to V ˙ O 2max at 4500m (r =-0.81, P  0.01) and 2500 m (r =-0.81, P  0.01), but not below. Furthermore, we noted a relationship between SpO 2 and O 2 pulse (V ˙ O 2 /HR) at every F I O 2 . Conclusion: These results demonstrate that endurance-trained women show a greater decrement in V ˙ O 2max at high altitudes. This could be explained mainly by a higher arterial desaturation, which is largely caused, according to our results, by diffusion limitation. Key Words: ALTITUDE, PERFORMANCE, ARTERIAL OXYGEN SATURATION, FEMALE T he changes in aerobic performance at various levels of hypoxia are well documented in men. On the contrary, very few such studies have been carried out on women. Yet men and women may not have similar metabolic responses during maximal exercise in acute hyp- oxia. Besides, some studies report a greater decrease in maximal oxygen consumption (V ˙ O 2max ) in men (10,24,28). Some authors hypothesize that women have a stronger pro- tective mechanism against acute exposure to hypoxia during maximal exertion because of a higher relative ventilatory response than males of similar age (24). Consequently, a better hyperventilation could enhance arterial oxygen satu- ration (SaO 2 ) and oxygen delivery to the active muscles (34). Other investigators found a higher ventilatory equiv- alent (V ˙ E/V ˙ O 2max ) in women at maximal exercise without a lesser SaO 2 (10). But despite this assumed adaptive phe- nomenon, some studies did not find any difference in gender concerning V ˙ O 2max decrement in acute hypoxia (35), and others even reported a higher decrease in women (6,31). These conflicting results could be partly explained by 1) a low number of subjects in some studies, 2) differences in fitness level between males and females, and 3) participa- tion of acclimated subjects. Furthermore, the few experiments carried out in women concerned sedentary or physically active, but very rarely endurance-trained, subjects. It would appear important for this population (endurance-trained subjects), for practical reasons, to know the changes in performance with altitude. Indeed, training intensity at altitude must be calculated by taking these changes into account to avoid overtraining or even undertraining. Moreover, if sedentary women can en- hance their ventilatory response in hypoxia, it is not certain that trained ones would be able to do so. In that respect, some authors report that women’s smaller lungs could affect hyperpnea, especially in highly fit women (21). These me- chanical constraints of ventilation may make it hard to maintain a high level of alveolar oxygen pressure (PAO 2 ) and consequently exacerbate the arterial desaturation, espe- cially at high altitude. The studies that have compared trained and sedentary men at maximal exercise in acute hypoxia report a higher drop of aerobic performance in the former (7,18,20). This could be mainly due to the greater arterial desaturation in Address for correspondence: Xavier Woorons, Laboratory of Functional and Cellular Responses to Hypoxia, 74 rue Marcel Cachin, 93017 Bobigny Cedex, France; E-mail: xwoorons@laposte.net. Submitted for publication May 2004. Accepted for publication August 2004. 0195-9131/05/3701-0147 MEDICINE & SCIENCE IN SPORTS & EXERCISE ® Copyright © 2005 by the American College of Sports Medicine DOI: 10.1249/01.MSS.0000150020.25153.34 147