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  • Title: A reduced lactate mass explains much of the glycogen sparing associated with training.
    Author: Crowley MA, Willis WT, Matt KS, Donovan CM.
    Journal: J Appl Physiol (1985); 1996 Jul; 81(1):362-7. PubMed ID: 8828686.
    Abstract:
    Endurance training is associated with glycogen (Gly) sparing, generally attributed to less carbohydrate (CHO) oxidation. However, untrained individuals commit a greater fraction of CHO to lactate (La), accounting for a portion of the Gly "spared." We examined the effects of training (running 1 h/day at 30 m/min up an 8 degrees grade) on whole body CHO distribution and oxidation. Female Long Evans rats (n = 27) were assigned to control (Untr) and trained (Tr) groups. Two days before the experiment, animals were chronically catheterized. On the day of the experiment, animals ran for 20 min at a speed of 28 m/min and were killed with an overdose of pentobarbital sodium injection while running. Whole carcasses were then promptly freeze-clamped with a liquid N2-cooled press. Whole body carcass powder was assayed for La, Gly, and glucose. Resting whole body values were not different between groups (La = 0.78 +/- 0.06 vs. 0.83 +/- 0.07, Gly = 4.46 +/- 0.62 vs. 3.77 +/- 0.35, glucose = 0.19 +/- 0.07 vs. 0.23 +/- 0.09 mmol/body for Tr and Untr rats, respectively). However, postexercise La was higher in Untr vs. Tr group (2.01 +/- 0.28 vs. 1.13 +/- 0.09 mmol/body), and Gly was lower in the Untr vs. Tr rats (1.58 +/- 0.25 vs. 3.42 +/- 0.43 mmol/body). Similarly, Untr animals displayed higher epinephrine levels than Tr at the end of the exercise bout (4.9 +/- 1.0 vs. 1.7 +/- 0.4 ng/ml). Differences between groups in La and glucose masses (postexercise minus rest data) accounted for 60% of the Gly differences. Gly spared from oxidation and replaced by increased fat oxidation only accounted for 40% of the differences in Gly levels between Tr and Untr animals. We conclude that untrained mammals commit a significant portion of their CHO pool to La, which accounts for almost one-half of the apparent Gly spared during moderate-intensity exercise in the trained state.
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