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

Abstract

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 the 1930s is the phenomenon referred to as the 'lactate paradox'. Acute exposure 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 accumulation at submaximal work and peak blood lactate levels are paradoxically reduced compared with those at sea level. It has recently been shown, however, that, if the exposure to altitude is sufficiently long, blood lactate responses return to those seen at sea level or during acute hypoxia. Thus, to evaluate the 'lactate paradox' phenomenon in relation to time spent at altitude, five Danish lowland climbers were studied at sea level, during acute exposure to hypoxia (10% O2 in N2) and 1, 4 and 6 weeks after arrival in the basecamp of Mt Everest (approximately 5400 m, Nepal). Basecamp was reached after 10 days of gradual ascent from 2800 m. Peak blood lactate levels were similar at sea level (11.0 +/- 0.7 mmol L-1) and during acute hypoxia (9.9 +/- 0.3 mmol 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 still lower compared with acute hypoxia but higher than that seen after 1 week of acclimatization. After 6 weeks of acclimatization, 2 days after return 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 acute hypoxia. Therefore, these results suggest that the 'lactate paradox' is a transient metabolic phenomenon that is reversed during a prolonged period of exposure to severe hypoxia of more than 6 weeks.

Similar carbohydrate but enhanced lactate utilization during exercise after 9 wk of acclimatization to 5,620 m

“…However, evidence has been presented that the blunted blood lactate concentration in the course of acclimatization is transient. After 7 wk of acclimatization to high altitude (5,400 m), the blood lactate concentration was similar to what was observed in acute hypoxia (22). Furthermore, during submaximal and maximal bicycle work, net lactate release from the active legs has been reported to be lower with acute compared with chronic exposure to hypoxia (32).…”

“…After several weeks of acclimatization to hypoxia, the blood lactate response to a given workload is blunted, i.e., the "lactate paradox" (33), although this concept has been challenged (22,32). So far, only one study is available describing in more detail whole body and muscle carbohydrate and lactate metabolism at rest and during exercise after a relatively short period of 3 wk of acclimatization to altitude (3,4,5).…”

Supramaximal Exercise

“…This led to the hypothesis that the lactate paradox might follow a fall of lactate transport outside muscle fibres, perhaps due to reduced activity of the lactate-proton co-transporter. If the acclimatization process is prolonged beyond 6 weeks, maximal lactic capacity progressively recovers, until the differences between acute and chronic hypoxia disappear (Lundby et al 2000), suggesting that the lactate paradox may be a transient phenomenon. In fact the rate of lactate outflow from muscle fibres to blood increases with time at altitude, which implies also an increase in the rate of lactate removal from blood by lactate metabolizing organs, such as liver, brain, kidneys and heart, and eventually also noncontracting muscles.…”

Limiting factors to oxygen transport on Mount Everest 30�years after: a critique of Paolo Cerretelli?s contribution to the study of altitude physiology

“…In my view, these data altogether support the hypothesis that the lactate paradox may reflect a reduction of proton transport outside the muscle fibre, perhaps due to a reduced activity of the lactate-proton co-transporter. More recently, SaltinÕs group has shown that there are no differences in maximal blood lactate concentration between chronic hypoxia and normoxia if acclimatisation to altitude is prolonged beyond 6 weeks (Lundby et al 2000;van Hall et al 2001), suggesting that the lactate paradox may be a transient phenomenon. This has led to a slight modification of this hypothesis, as the possibility of a progressive upregulation of the lactate-proton co-transporter with time of acclimatisation had to be postulated (van Hall et al 2001), but not to its refutation.…”