Relating Intramuscular Fuel Use to Endurance in Juvenile Rainbow Trout

Abstract This study examined fuel depletion in white muscle of juvenile rainbow trout sprinted to fatigue to determine whether the onset of fatigue is associated with a measurable metabolic change within the muscle and whether muscle glycogen levels influence endurance. In this study, “fuels” refer to any energy‐supplying compounds and include glycogen, phosphocreatine (PCr), and ATP. Fuel depletion in white muscle was estimated by the calculation of the anaerobic energy expenditure (AEE; in μmol ATP equivalents g−1) from the reduction of PCr and ATP and the accumulation of lactate. Progression of fuel use during sprinting was examined by sampling fish before they showed signs of fatigue and following fatigue. Most of the AEE before fatigue was due to PCr depletion. However, at the first signs of fatigue, there was a 32% drop in ATP. Similarly, when fish were slowly accelerated to a fatiguing velocity, the only significant change at fatigue was a 30% drop in ATP levels. Muscle glycogen levels were manipul...