Bassett D R, Howley E T
Department of Exercise Science and Sport Management, University of Tennessee, Knoxville 37996, USA.
Med Sci Sports Exerc. 2000 Jan;32(1):70-84. doi: 10.1097/00005768-200001000-00012.
In the exercising human, maximal oxygen uptake (VO2max) is limited by the ability of the cardiorespiratory system to deliver oxygen to the exercising muscles. This is shown by three major lines of evidence: 1) when oxygen delivery is altered (by blood doping, hypoxia, or beta-blockade), VO2max changes accordingly; 2) the increase in VO2max with training results primarily from an increase in maximal cardiac output (not an increase in the a-v O2 difference); and 3) when a small muscle mass is overperfused during exercise, it has an extremely high capacity for consuming oxygen. Thus, O2 delivery, not skeletal muscle O2 extraction, is viewed as the primary limiting factor for VO2max in exercising humans. Metabolic adaptations in skeletal muscle are, however, critical for improving submaximal endurance performance. Endurance training causes an increase in mitochondrial enzyme activities, which improves performance by enhancing fat oxidation and decreasing lactic acid accumulation at a given VO2. VO2max is an important variable that sets the upper limit for endurance performance (an athlete cannot operate above 100% VO2max, for extended periods). Running economy and fractional utilization of VO2max also affect endurance performance. The speed at lactate threshold (LT) integrates all three of these variables and is the best physiological predictor of distance running performance.
在运动的人体中，最大摄氧量（VO2max）受心肺系统向运动肌肉输送氧气能力的限制。这由三条主要证据表明：1）当氧气输送发生改变（通过血液兴奋剂、低氧或β受体阻滞剂）时，VO2max会相应改变；2）VO2max随训练增加主要源于最大心输出量的增加（而非动静脉氧差的增加）；3）当一小块肌肉在运动期间过度灌注时，它具有极高的耗氧能力。因此，氧气输送而非骨骼肌的氧气摄取被视为运动人体中VO2max的主要限制因素。然而，骨骼肌的代谢适应对于提高次最大耐力表现至关重要。耐力训练会导致线粒体酶活性增加，通过在给定VO2下增强脂肪氧化和减少乳酸积累来提高表现。VO2max是设定耐力表现上限的重要变量（运动员不能长时间在超过100%VO2max的水平下运作）。跑步经济性和VO2max的分数利用率也会影响耐力表现。乳酸阈（LT）速度整合了这三个变量，并且是长跑表现的最佳生理预测指标。
