The 'lactate paradox', evidence for a transient change in the course of acclimatization to severe hypoxia in lowlanders

The metabolic response to exercise at high altitude is different from that at sea level, depending on the altitude. the rate of ascent and duration of acclimatization. One apparent metabolic difference that was described in t he 1930s is the phenomenon referred to as the 'lactate paradox'. Acute expo sure to hypoxia results in higher blood lactate accumulation at submaximal workloads compared with sea level, but peak blood lactate remain the same. Following continued exposure to hypoxia or altitude, blood lactate accumula tion at submaximal work and peak blood lactate levels are paradoxically red uced compared with those at sea level. It has recently been shown, however, that, if the exposure to altitude is sufficiently long, blood lactate resp onses return to those seen at sea level or during acute hypoxia. Thus, to e valuate the 'lactate paradox' phenomenon in relation to time spent at altit ude, five Danish lowland climbers were studied at sea level. during acute e xposure to hypoxia (10% O-2 in N-2) and 1, 4 and 6 weeks after arrival in t he basecamp of Mt Everest (-5400 m, Nepal). Basecamp was reached after 10 d ays of gradual ascent from 2800 m. Peak blood lactate levels were similar a t sea level (11.0 +/- 0.7 mmol L-1) and during acute hypoxia (9.9 +/- 0.3 m mol L-1), but fell significantly after 1 week of acclimatization to 5400 m (5.6 +/- 0.5 mmol L-1) as predicted by the 'lactate paradox'. After 4 weeks of acclimatization, peak lactate accumulation (7.8 +/- 1.0 mmol L-1) was s till lower compared with acute hypoxia but higher than that seen after 1 we ek of acclimatization. After 6 weeks of acclimatization, 2 days after retur n to basecamp after reaching the summit or south summit of Mt Everest, peak lactate levels (10.4 +/- 1.1 mmol L-1) were similar to those seen during a cute hypoxia. Therefore, these results suggest that the 'lactate paradox' i s a transient metabolic phenomenon that is reversed during a prolonged peri od of exposure to severe hypoxia of more than 6 weeks.