A reduced lactate mass explains much of the glycogen sparing associated with training

Michael A. Crowley, Wayne T. Willis, Kathleen S. Matt, Casey M. Donovan

Research output: Contribution to journalArticle

10 Scopus citations

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° 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.

Original languageEnglish (US)
Pages (from-to)362-367
Number of pages6
JournalJournal of Applied Physiology
Volume81
Issue number1
DOIs
StatePublished - Jul 1996

Keywords

  • carbohydrate metabolism
  • endurance exercise
  • metabolic regulation

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)

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