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Medicine & Science in Sports & Exercise:
BASIC SCIENCES: Commentaries

Limiting factors for maximum oxygen uptake and determinants of endurance performance

BASSETT , DAVID R. JR. EDWARD T. HOWLEY

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Abstract

BASSETT, D. R., JR. and E. T. HOWLEY. Limiting factors for maximum oxygen uptake and determinants of endurance performance. Med. Sci. Sports Exerc., Vol. 32, No. 1, pp. 70–84, 2000. In the exercising human, maximal oxygen uptake (V̇O2max) 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), V̇O2max changes accordingly; 2) the increase in V̇O2max with training results primarily from an increase in maximal cardiac output (not an increase in the a-v̄ 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 V̇O2max 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 V̇O2. V̇O2max is an important variable that sets the upper limit for endurance performance (an athlete cannot operate above 100% V̇O2max. for extended periods). Running economy and fractional utilization of V̇O2max 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.

Maximum oxygen uptake (V̇O2max ) is defined as the highest rate at which oxygen can be taken up and utilized by the body during severe exercise. It is one of the main variables in the field of exercise physiology, and is frequently used to indicate the cardiorespiratory fitness of an individual. In the scientific literature, an increase in V̇O2max is the most common method of demonstrating a training effect. In addition, V̇O2max is frequently used in the development of an exercise prescription. Given these applications of V̇O2max, there has been great interest in identifying the physiological factors that limit V̇O2max and determining the role of this variable in endurance performance.

The current concept of V̇O2max began with the work of Hill et al. (41,42) in 1923–24. Their view of maximum oxygen uptake has been validated, accepted, and extended by many world-renowned exercise physiologists (2,17,58,68,74,83). However, it has recently been argued that Hill’s V̇O2max paradigm is an outdated concept, based upon critical flaws in logic (62). To consider these points of view, we weighed the arguments on both sides and concluded in 1997 (5) that the “classical” view of V̇O2max was correct. The present article is an attempt to clarify our views on V̇O2max and to present further evidence in support of Hill’s theory.

Part I of this article reviews the history of the concept of V̇O2max. Part II describes the evidence for each of the four potentially limiting factors for V̇O2max. Part III discusses the role of V̇O2max and other factors in determining endurance performance.

©2000The American College of Sports Medicine

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