VO2 Max Essentials Part II: Determinants of Endurance Performance

The underlying physiology of champions.

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As we discussed in part I of this series, VO2 max refers to your maximal rate of oxygen consumption.

Elite endurance athletes typically exhibit significantly higher VO2 max values compared to sedentary individuals, and for this reason, VO2 max is quite often used as the “gold standard” for measuring endurance performance potential. It’s also commonly used to objectively measure adaptations to training and as an outcome in research studies in exercise physiology.

A higher VO2 max in elite athletes can be attributed to various physiological adaptations resulting from training, including increased cardiac stroke volume, blood volume, capillary density, and mitochondrial density and efficiency.

You can think of VO2 max as the ceiling of aerobic performance. However, most endurance events occur at an intensity well below VO2 max. While having a high ceiling is a prerequisite for elite-level performance, it’s hardly the determining factor in who will win a race.

Indeed, during endurance events lasting longer than 10 to 15 minutes, most of the competition occurs at an average pace that does not elicit VO2 max — a submaximal intensity. For example, marathon runners typically maintain a pace of approximately 75-85% of their VO2 max, while shorter races like the 10 km and 5 km are performed at higher intensities. Interestingly, studies have shown that the maximal aerobic metabolism can decline during a race, particularly in shorter-duration bouts, due to factors such as reduced stroke volume, muscle fatigue, decreased blood and oxygen delivery, and increased anaerobic metabolism. This highlights the dynamic nature of aerobic energy production and ATP resynthesis during competition.

If VO2 max isn’t the determining factor for endurance performance, then what is? Currently, there are a few different metrics that can explain much of the performance variation among athletes, these include lactate threshold, performance VO2, and efficiency. A complex interplay among these factors determines the power or speed that someone can maintain during a race of a certain duration or length, and ultimately, who ends up victorious.¹

Lactate threshold

Lactate threshold refers to the exercise intensity at which there is a sustained rise in blood lactate levels. It is an important concept for endurance performance as it reflects the point at which aerobic metabolism becomes insufficient to meet the ATP demands of muscles, and more ATP must be synthesized using anaerobic pathways. When the rate of pyruvate delivery to the mitochondria exceeds the mitochondria's capacity to oxidize it, lactate production increases. The accumulation of lactate and the associated release of hydrogen ions are believed to contribute to muscle fatigue and trigger important cardiovascular and autonomic reflexes that limit performance. However, fatigue is complex and influenced by many other factors, including fuel availability.

The lactate threshold is influenced by the oxidative capacity of the skeletal muscles, which can be enhanced through training. Elite endurance athletes often exhibit higher lactate threshold values compared to sedentary individuals, as their oxidative capacity is significantly increased. This means that elite athletes can sustain higher absolute oxygen consumption, power output, and speed for extended periods before reaching their lactate threshold. This allows them to maintain sustained running speeds of up to 20 km/h or cycling power outputs of 400 W — much higher than mere mortals.

Another factor that affects muscle fatigability and lactate production during exercise near the lactate threshold is the amount of muscle mass recruited.