Exercise at high altitude is associated with an increase in lactate in comparison to exercise of similar workloads at sea level. However, with continuing exposure to high altitude, the peak lactate levels fall with exercise (the 'lactate paradox') and finally revert to similar levels seen during exercise at sea level. The proportional contribution of lactate to exercise performance is however unknown. This is the first report of the effect of acclimatisation to high altitude on the ventilatory threshold measured during cardiopulmonary exercise testing in humans. The ventilatory threshold was used to quantify the proportional contribution of aerobic and oxygen-in-dependent metabolism to exercise performance with acclimatisation to high altitude. Eight lowlander subjects underwent cardiopulmonary exercise testing with an alticycle cycle ergometer in Coventry (80 m) and on arrival in Leh, India (3500 m) and after 12 days acclimatization. The VO2 peak was reduced on arrival at high altitude and remained depressed at 12 days. The ventilatory threshold was depressed on arrival at high altitude, and was further depressed at 12 days. The ventilatory threshold as a proportion of the VO2 peak was decreased on arrival at high altitude, and with acclimatisation, this relationship was further decreased. This study suggests that with high altitude acclimatisation the proportional contribution of oxygen-independent metabolism to exercise performance increases, while conversely the contribution of oxygen-dependent metabolism to exercise performance decreases.
© Copyright 2006 High Altitude Medicine & Biology. Mary Ann Liebert. All rights reserved.