McFarlane W J, McDonald D G
Department of Biology, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada.
Physiol Biochem Zool. 2002 May-Jun;75(3):250-9. doi: 10.1086/341815.
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 micromol 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 manipulated by altering ration (1% vs. 4% body weight ration per day) combined with either daily or no exercise. Higher ration alone led to significantly greater muscle glycogen but had no effect on sprint performance, whereas sprint training led to higher glycogen and an average threefold improvement in sprint performance. In contrast, periodic chasing produced a similar increase in glycogen but had no effect on sprint performance. Taken together, these observations suggest that (i) a reduction in ATP in white muscle could act as a proximate signal for fatigue during prolonged exercise in fish and (ii) availability of muscle glycogen does not limit endurance.
本研究检测了 sprint 至疲劳的幼年虹鳟鱼白肌中的燃料消耗情况，以确定疲劳的发生是否与肌肉内可测量的代谢变化相关，以及肌肉糖原水平是否会影响耐力。在本研究中，“燃料”指任何提供能量的化合物，包括糖原、磷酸肌酸（PCr）和三磷酸腺苷（ATP）。通过计算 PCr 和 ATP 的减少以及乳酸的积累所产生的无氧能量消耗（AEE；以微摩尔 ATP 当量 g(-1) 为单位）来估算白肌中的燃料消耗。在鱼出现疲劳迹象之前和之后对其进行采样，以检测 sprint 过程中燃料的使用进程。疲劳前的大部分 AEE 是由于 PCr 的消耗。然而，在出现疲劳的最初迹象时，ATP 下降了 32%。同样，当鱼缓慢加速至疲劳速度时，疲劳时唯一显著的变化是 ATP 水平下降了 30%。通过改变日粮（每天 1%体重日粮与 4%体重日粮）并结合每日运动或不运动来控制肌肉糖原水平。仅较高的日粮会导致肌肉糖原显著增加，但对 sprint 表现没有影响，而 sprint 训练会导致糖原增加，并且 sprint 表现平均提高三倍。相比之下，定期追逐会使糖原产生类似的增加，但对 sprint 表现没有影响。综上所述，这些观察结果表明：（i）在鱼类长时间运动过程中，白肌中 ATP 的减少可能作为疲劳的直接信号；（ii）肌肉糖原的可用性并不限制耐力。
