Blood glucose responses in humans mirror lactate responses for individual anaerobic threshold and for lactate minimum in track tests

Abstract

The equilibrium point between blood lactate production and removal (La⁻ _min) and the individual anaerobic threshold (IAT) protocols have been used to evaluate exercise. During progressive exercise, blood lactate [La⁻]_b, catecholamine and cortisol concentrations, show exponential increases at upper anaerobic threshold intensities. Since these hormones enhance blood glucose concentrations [Glc]_b, this study investigated the [Glc] and [La⁻]_b responses during incremental tests and the possibility of considering the individual glucose threshold (IGT) and glucose minimum (Glc_min) in addition to IAT and La⁻ _min in evaluating exercise. A group of 15 male endurance runners ran in four tests on the track 3000 m run (v _3km); IAT and IGT – 8 × 800 m runs at velocities between 84% and 102% of v _3km; La⁻ _min and Glc_min– after lactic acidosis induced by a 500-m sprint, the subjects ran 6 × 800 m at intensities between 87% and 97% of v _3km; endurance test (ET) – 30 min at the velocity of IAT. Capillary blood (25 μl) was collected for [La⁻]_b and [Glc]_b measurements. The IAT and IGT were determined by [La⁻]_b and [Glc]_b kinetics during the second test. The La⁻ _min and Glc_min were determined considering the lowest [La⁻] and [Glc]_b during the third test. No differences were observed (P < 0.05) and high correlations were obtained between the velocities at IAT [283 (SD 19) and IGT 281 (SD 21) m. · min⁻¹; r = 0.096; P < 0.001] and between La⁻ _min [285 (SD 21)] and Glc_min [287 (SD 20) m. · min⁻¹ r = 0.77; P < 0.05]. During ET, the [La⁻]_b reached 5.0  (SD 1.1) and 5.3 (SD 1.0) mmol · l⁻¹ at 20 and 30 min, respectively (P > 0.05). We concluded that for these subjects it was possible to evaluate the aerobic capacity by IGT and Glc_min as well as by IAT and La⁻ _min.