Abstract
Glucose-fructose ingestion increases glucose and lactate oxidation during exercise. We hypothesized that training with glucose-fructose would induce key adaptations in lactate metabolism. Two groups of eight sedentary males were endurance-trained for three weeks while ingesting either glucose-fructose (GF) or water (C). Effects of glucose-fructose on lactate appearance, oxidation, and clearance were measured at rest and during exercise, pre-training, and post-training. Pre-training, resting lactate appearance was 3.6 ± 0.5 vs. 3.6 ± 0.4 mg·kg−1·min−1 in GF and C, and was increased to 11.2 ± 1.4 vs. 8.8 ± 0.7 mg·kg−1·min−1 by exercise (Exercise: p < 0.01). Lactate oxidation represented 20.6 ± 1.0% and 17.5 ± 1.7% of lactate appearance at rest, and 86.3 ± 3.8% and 86.8 ± 6.6% during exercise (Exercise: p < 0.01) in GF and C, respectively. Training with GF increased resting lactate appearance and oxidation (Training × Intervention: both p < 0.05), but not during exercise (Training × Intervention: both p > 0.05). Training with GF and C had similar effects to increase lactate clearance during exercise (+15.5 ± 9.2 and +10.1 ± 5.9 mL·kg−1·min−1; Training: p < 0.01; Training × Intervention: p = 0.97). The findings of this study show that in sedentary participants, glucose-fructose ingestion leads to high systemic lactate appearance, most of which is disposed non-oxidatively at rest and is oxidized during exercise. Training with or without glucose-fructose increases lactate clearance, without altering lactate appearance and oxidation during exercise.
Highlights
During moderate and high intensity exercise, muscle energy needs are essentially met by carbohydrate oxidation [1] and muscle performance is dependent on both muscle glycogen and plasma glucose concentrations [2,3,4]
Lactate can be recycled into glucose, with recent indications that this can be altered in trained subjects [10,11]
Glucose-fructose ingestion increased blood lactate concentration compared to fasting values
Summary
During moderate and high intensity exercise, muscle energy needs are essentially met by carbohydrate oxidation [1] and muscle performance is dependent on both muscle glycogen and plasma glucose concentrations [2,3,4]. Plasma glucose entry into skeletal muscle is activated by contraction [5] and depends on systemic glucose appearance, i.e., the sum of endogenous glucose production (hepatic glycogen breakdown and gluconeogenesis) and gut glucose absorption [1,6]. A portion of glucose is made indirectly available through glycolytic lactate production in some muscle fibers, followed by lactate uptake and oxidation in other fibers [7]. Nutrients 2017, 9, 411 muscle energy substrates provision when glucose transport and/or glycolytic capacity is saturated. Lactate can be recycled into glucose (gluconeogenesis), with recent indications that this can be altered in trained subjects [10,11]
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