Tschakert, G., Ofner, M., Wonisch, M., Frei, M., Domej, W., Kroepfl, J., Mueller, A., Moster, O., & Hofmann, P. (2014). Determination of lactate turn points in normoxic and hypoxic conditions. Medicine & Science in Sports & Exercise, 46(5), Supplement abstract number 1569.

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This study compared the first and second lactate turn-points to standard first and second ventilatory thresholds and to the heart rate turn-point and evaluated power output as well as the response of physiological variables to incremental exercise in normobaric hypoxia and normoxia. Healthy men (N = 10) performed two maximal incremental exercise tests on a cycle ergometer in normoxia and normobaric hypoxia (14% O2) in randomized order. Maximum and turn-point values of power output, blood-lactate concentration, gas exchange variables, and heart rate, as well as the deflection of the heart rate performance curve were measured in both conditions.

No significant differences but significant correlations were found between lactate turn-point 1 and the first ventilatory threshold as well as between lactate turn-point 2 and the second ventilatory threshold and between lactate turn-point 2 and heart rate turn-point for power in both conditions. In hypoxia, power at lactate turn-point 1 and lactate turn-point 2 was significantly reduced compared to normoxia in absolute terms but not significantly different in relative terms (% maximum power). Maximum heart rate, maximal oxygen uptake (VO2max ), and maximum power were significantly decreased in normobaric hypoxia compared to normoxia, and the amount of maximum-power reduction in normobaric hypoxia was significantly related to normoxic maximum power and power output at lactate turn-point 2. A significant difference was found for the heart rate performance curve deflection between normobaric hypoxia and mormoxia.

Implication. The lactate turn-point determination is suggested to be a valid and reliable method in normoxic and normobaric hypoxic conditions. The pattern of the lactate performance curve was stable independent of oxygen availability, and therefore power output at lactate turn-point 1 and power output at lactate turn-point 2 expressed as percent of maximum power were equal between the two conditions. Maximum power output in normoxia was shown to be significantly related to the decrease of maximum power in normobaric hypoxia.

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