Paper
Circadian rhythms in blood lactate concentration during incremental ergometer rowing
Published Feb 26, 2004 · J. Forsyth, T. Reilly
European Journal of Applied Physiology
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Abstract
This study examined whether circadian rhythms affect lactate threshold (Th_lac) during rowing exercise. Eleven male, endurance-trained athletes [mean (SD) age 29.5 (6.1) years] rowed at 0200, 0600, 1000, 1400, 1800 and 2200 hours under the same experimental conditions. Capillary blood (25 μl) was obtained from the tip of the toe during the last 30 s of a continuous, multi-stage, 3-min, incremental protocol on the Concept II ergometer. To determine Th_lac, a curve-fitting procedure (the D _max method), a visual method (Th_lac-vis) and the fixed blood lactate concentration of 4.0 mmol l^−1 (Th_lac-4 mM) were used. Circadian rhythms were apparent for oxygen consumption and heart rate at Th_lac using the D _max method (P=0.02 and P=0.04 respectively), with the acrophases at 2139 hours and 2032 hours respectively coinciding in phase with that of core body temperature. The conclusion is that tests should be completed at the same time of day at which the athlete usually trains, to ensure precision of Th_lac determination, especially when the D _max method is used to determine Th_lac.
Tests should be completed at the same time of day as the athlete normally trains to ensure precision in blood lactate threshold determination during rowing exercise.
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