title: Persistence of the lactate paradox over 8 weeks at 3,800 m.
abstract: The arterial blood lactate [La] response to exercise increases in acute hypoxia, but returns to near the normoxic (sea level, SL) response after 2 to 5 weeks of altitude acclimatization. Recently, it has been suggested that this gradual return to the SL response in [La], known as the lactate paradox (LP), unexpectedly disappears after 8 to 9 weeks at altitude. We tested this idea by recording the [La] response to exercise every 2 weeks over 8 weeks at altitude. Five normal, fit SL-residents were studied at SL and 3,800 m (Pbar = 485 torr) in both normoxia (PIO2 = 150 torr) and hypoxia (PIO2 = 91 torr approximately air at 3,800 m). Arterial [La] and blood gas values were determined at rest and during cycle exercise at the same absolute workloads (0, 25, 50, 75, 90, and 100% of initial SL-VO2Max) and exercise duration (4, 4, 4, 2, 1.5, and 0.75 min, respectively) at each time point. [La] curves were elevated in acute hypoxia at SL (p < 0.01) and at 3,800 m fell progressively toward the SL-normoxic curve (p < 0.01). On the same days, [La] responses in acute normoxia showed essentially no changes over time and were similar to initial SL normoxic responses. We also measured arterial catecholamine levels at each load and found a close relationship to [La] over time, supporting a role for adrenergic influence on [La]. In summary, extending the time at this altitude to 8 weeks produced no evidence for reversal of the LP, consistent with prior data obtained over shorter periods of altitude residence.
authors.affiliation: Division of Physiology, Department of Medicine, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Marieke
authors.initials: M
authors.lastname: Pronk
authors.forename: Ivo
authors.initials: I
authors.lastname: Tiemessen
authors.forename: Maarten D W
authors.initials: MD
authors.lastname: Hupperets
authors.forename: Brian P
authors.initials: BP
authors.lastname: Kennedy
authors.forename: Frank L
authors.initials: FL
authors.lastname: Powell
authors.forename: Susan R
authors.initials: SR
authors.lastname: Hopkins
authors.forename: Peter D
authors.initials: PD
authors.lastname: Wagner
mesh_terms: D000064:Acclimatization; D000328:Adult; D000531:Altitude; D000704:Analysis of Variance; D002140:California; D004837:Epinephrine / Q000097:blood; D015444:Exercise; D005080:Exercise Test; D005260:Female; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D019344:Lactic Acid / Q000097:blood*; D008297:Male; D009051:Mountaineering; D009638:Norepinephrine / Q000097:blood; D012016:Reference Values; D013997:Time Factors
chemical_list: D019344:Lactic Acid; D009638:Norepinephrine; D004837:Epinephrine