Somewhere, right now, a runner is checking their watch for a VO2 max estimate. The number glows with authority. 48. Or 52. Or 41. It rises and falls by fractions, and with it, so does their sense of fitness. The metric has become the measure of the runner. But here is what the devotees of the number do not discuss: elite athletes have watched their VO2 max decline while they ran the fastest times of their lives.
VO2 max, which is the maximum rate at which your body can consume oxygen during exercise, has been treated as the gold standard of endurance fitness since the mid-20th century. It is measurable. It sounds scientific. It provides a number to optimize. And it has been catastrophically overvalued.
What VO2 Max Actually Is
Let us first understand what we are measuring. VO2 max represents the ceiling of your aerobic system—the maximum amount of oxygen your heart can pump and your muscles can use per minute, typically expressed relative to body weight (ml/kg/min). It is determined by cardiac output, oxygen-carrying capacity of the blood, and the ability of muscles to extract and use oxygen.
Higher is generally better. The average untrained person might have a VO2 max of 35-40 ml/kg/min. Recreational runners often reach 45-55. Elite marathoners may hit 70-85. The highest recorded values approach 90-97 in cross-country skiers and cyclists.
The assumption has been that improving this number improves performance. The research tells a more complicated story.
When Elite Athletes Got Slower VO2 Max and Faster Times
The most fascinating evidence against VO2 max supremacy comes from longitudinal studies of elite athletes that followed the same individuals over years or even decades of training and racing.
Studies of elite distance runners have documented cases where athletes improved their race performances while their VO2 max stayed the same or even declined. The improvements came not from a larger aerobic engine but from using the existing engine more efficiently.
Perhaps the most cited example comes from research on elite Kenyan and Ethiopian runners by Billat and others, showing that world-class marathoners often have VO2 max values in the high 70s—excellent, but not exceptional. What distinguishes them is running economy and lactate threshold, not raw oxygen processing capacity.
Studies tracking individual elite runners over multi-year periods have shown performance improvements of 2-3% while VO2 max remained stable or decreased slightly with age.
— Jones (2006); Lucia et al. (2006); Billat et al. (2003)
How is this possible? Because VO2 max is only one factor among many. Performance depends on what percentage of that VO2 max you can sustain (fractional utilization), how economically you convert oxygen into forward motion (running economy), and where your lactate threshold sits relative to your maximum capacity.
The Factors That Matter More
If VO2 max is not the sole determinant of performance, what is? Research points to several factors that predict race times better:
Running Economy
Running economy measures how much oxygen you require to run at a given pace. Two runners with identical VO2 max values can have dramatically different race performances based on economy alone. The more economical runner covers more ground with each liter of oxygen consumed.
Economy improves with training, particularly high-mileage training over years. It is influenced by biomechanics, muscle fiber characteristics, tendon stiffness, and neuromuscular coordination. Critically, economy can improve even when VO2 max does not.
Research by Conley and Krahenbuhl found that among runners with similar VO2 max values, running economy explained 65% of the variance in 10K race performance. The runner with the higher VO2 max did not always win. The more economical runner often did.
— Conley & Krahenbuhl (1980); Saunders et al. (2004)
Lactate Threshold
Your lactate threshold (the intensity at which lactate begins to accumulate faster than it can be cleared) determines what percentage of your VO2 max you can sustain. An athlete who can race at 90% of VO2 max will outperform one who can only sustain 80%, even if the latter has a higher maximum.
Lactate threshold is highly trainable and responds well to tempo runs, threshold intervals, and progressive long runs. Improvements here translate directly to race performance.
Fractional Utilization
Elite marathoners can sustain 85-90% of their VO2 max for over two hours. Average runners might sustain 70-75%. This ability to use a higher fraction of available capacity is developed through years of endurance training and is often what separates good runners from great ones.
Durability and Fatigue Resistance
How well do your systems hold up over distance and time? Can you maintain economy and threshold pace deep into a race when others are falling apart? This durability is developed through long runs, high-volume training, and race experience. None of which show up in a VO2 max test.
The Watch Estimate Problem
Beyond the conceptual limitations, there is a practical problem: most runners have never actually measured their VO2 max. They rely on estimates from GPS watches and fitness platforms.
The number on your watch is a guess based on algorithms that infer oxygen consumption from pace and heart rate. It is not a measurement. It is a prediction with substantial error.
These estimates can be off by 5-15% or more. They are influenced by course terrain, weather, how recently you did hard efforts, and whether the algorithm's assumptions match your physiology. A hilly run on a hot day might crater your estimated VO2 max. A downhill-assisted personal best might inflate it. Neither reflects actual changes in your aerobic capacity.
Treating these estimates as precise measurements of fitness leads to anxiety, confusion, and poor training decisions.
The Liberation
The next time your watch displays a VO2 max estimate, recognize it for what it is: one indirect, error-prone approximation of one factor among many that influence your running. It is not your identity. It is not your potential. It is not even particularly accurate.
Elite athletes have set personal bests and won championships while their measured VO2 max declined. They got better not by raising the ceiling but by improving everything else. Economy. Threshold. Durability. Race craft. Mental fortitude.
You can do the same.
Run more. Run consistently. Do your long runs. Hit your workouts. Recover properly. Trust the process over years, not the number over weeks. The path to faster running passes through the accumulated wisdom of the body, not the algorithmic pronouncements of the wrist.
The number does not define you. The miles do.
