Experimental fish were sprint trained by individual chasing for 30 s on alternate days for 9 weeks. Ten trained and 10 untrained animals were rapidly freezeclamped at rest and 0, 1, 3 and 6h after a 5-min chase. Swimming speed of 10 fish in each group was measured in a 2-min chase. Phosphocreatine (PCr), creatine, adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP), glycogen, glucose-1-phosphate (G-l-P), glucose-6-phosphate (G-6-P), fructose-6-phosphate (Fru-6-P), glucose, glycerol-3-phosphate (Glyc-3- P), pyruvate and lactate were measured on extracts from freeze-dried white muscle. Trained fish swam 14% further in 2min, with 90% of this difference occurring between 20 and 50 s. Trained fish accumulated 32% more lactate, but showed no differences in glycogen or PCr depletion, and 22% less ATP depletion, suggesting increased use of exogenous glucose. Glycogen repletion in early recovery, and lactate clearance between 1 and 3h after exercise, were also enhanced in trained fish. Energy stores (ATP equivalents) were higher after exercise and especially during recovery in trained fish. Overall, sprint training minimizes endogenous fuel depletion during exhaustive swimming, even though swim speed (and distance) increases, and enhances the rate of metabolic recovery following the swim.

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