title: A reduced lactate mass explains much of the glycogen sparing associated with training.
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.
authors.affiliation: Exercise and Sport Research Institute, Arizona State University, Tempe 85287-0404, USA.
authors.forename: M A
authors.initials: MA
authors.lastname: Crowley
authors.forename: W T
authors.initials: WT
authors.lastname: Willis
authors.forename: K S
authors.initials: KS
authors.lastname: Matt
authors.forename: C M
authors.initials: CM
authors.lastname: Donovan
mesh_terms: D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D001835:Body Weight / Q000502:physiology; D004837:Epinephrine / Q000097:blood; D005080:Exercise Test; D005260:Female; D005947:Glucose / Q000378:metabolism; D015309:Glucose Clamp Technique; D006003:Glycogen / Q000378:metabolism*; D019344:Lactic Acid / Q000378:metabolism*; D009638:Norepinephrine / Q000097:blood; D010101:Oxygen Consumption; D010805:Physical Conditioning, Animal; D010807:Physical Endurance / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology*; D051381:Rats; D012146:Rest / Q000502:physiology
chemical_list: D001786:Blood Glucose; D019344:Lactic Acid; D006003:Glycogen; D005947:Glucose; D009638:Norepinephrine; D004837:Epinephrine