Is VO2max correlated with running performance?

Artistic scatterplot showing 3k race times as a function of VO2max

Quite often I hear people claiming that “VO2max is not correlated with running performance.” Is that true?

What about similar correlation-based claims about metrics like body composition, running economy, mileage, and maximum heart rate?

Usually, when people make these kinds of claims, they link to a study showing that, among a certain group of runners, the metric in question (e.g. VO2max) does not accurately distinguish between the fastest and slowest runners in the group.

Another version of these claims comes in the form of statements like “among runners with a similar VO2max, those with better (running economy / lactate threshold / some other performance metric) have faster race times.”

So, what should we make of these kinds of claims? My goal in this article is to show why correlations will always become weaker when you restrict your analysis to a small subset of a population, like elite athletes.

Let's dig in and see why.

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Iron supplements, ferritin levels, and VO2max gains in athletes

Red blood cells in the style of a hand-drawn sketch

There’s a new study out this month on iron supplements for athletes with low ferritin. The study, published by Anja Neža Šmid and colleagues at the University of Ljubljana in Slovenia, is a meta-analysis, meaning it pooled data from several different randomized trials that took athletes, assigned them to either a placebo group or an iron supplement group, then measured the difference in ferritin levels between groups after the study’s conclusion.

The results of this meta-analysis are some of the strongest evidence that I’ve seen that support the notion that athletes with ferritin levels circa 20 ng/mL will benefit from an iron supplement. However, I wanted to write up this post because that’s actually not how the authors of the study interpret their own results!

Here’s what Smid et al. say in the abstract:

Increase in serum ferritin concentration after [oral iron supplementation] was evident in subjects with initial pre-supplementation serum ferritin concentration ≤12 µg/l [ ng/mL], while only minimal, if any effect, was observed in subjects with higher pre-supplementation serum ferritin concentration.

Šmid et al 2024

How can I justify the benefits of iron supplementation at 20 ng/mL, while the authors cite a cut-off value of barely half that level? Well, it all comes down to the way you analyze the data.

Here’s the bottom line up front: when treating ferritin level as a continuous number—which it is—the study’s data clearly show that runners with ferritin levels of around 20 ng/mL or less will experience significant increases in ferritin and gains in VO2max when taking an iron supplement over the course of 6–8 weeks.

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The science of critical speed, critical velocity (CV), and critical power training for runners

Female athlete running in front of scientific graphic paper

Critical speed is the boundary that separates running speeds that can be sustained at a metabolic steady-state from speeds that cannot. Sometimes called critical velocity or “CV,” critical speed is known in the running world in partly due to its popularization by Tom “Tinman” Schwartz and his proteges, including Drew Hunter.[1]

Critical speed is increasingly becoming the gold standard among physiologists for identifying the limit of what runners would call “high-end aerobic” or “steady-state” running speeds, and is gaining traction as a training tool as well. The critical speed model explains the body’s response to different speeds better than older models based on the lactate threshold.

Among exercise physiologists, critical speed (or a semi-related concept, the maximum lactate steady state, which we’ll also discuss) is rapidly becoming the gold standard for capturing the aerobic fitness of athletes.

Critical speed has its roots in early work in the 1960s, 70s, and 80s, but didn’t really start to emerge as the strongest physiological model for intense exercise until the last 15 years or so.

In this article, we’ll take a detailed look at the critical speed phenomenon, understand how it works on a mathematical and physiological level, see some of the problems and controversies surrounding it, and learn how to apply the concept of critical speed in your own training.

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Training intensity and capillary growth: Do you believe all the studies, or just a few? 

Color microscope image of muscle fibers and capillaries

Recently I’ve been diving back into the world of exercise physiology research, especially as it relates to running performance. I got behind on following ex phys in grad school (too busy following biomechanics!), so it’s been a few years since I’ve caught up on the latest research.

This weekend I was reading about capillarization: the growth of new, tiny blood vessels–capillaries–that run between and around individual muscle fibers. Capillaries are super important for aerobic performance, since they’re the place where oxygen diffuses out of red blood cells and into muscle fibers. 

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Review and summary of Marathon Training - A Scientific Approach by Renato Canova

Photo of the book Marathon Training - A Scientific Approach by Renato Canova and Enrico Arcelli

How do the best marathon runners in the world train? While you might catch a workout or two on Instagram or hear rumors about epic training weeks on message boards, there’s precious little information on the systematic approaches that elite coaches use with top marathon runners–and even less information on the science that backs up these approaches for designing marathon training programs.

One exception to this general rule has been the Italian coach Renato Canova, arguably the greatest living running coach and the topic of several of my previous posts on Running Writings. Canova freely discusses his training philosophy and posts example workouts or even full training schedules for the athletes he has worked with, which include Olympic and World Championships medallists.

In 1999, Canova even co-authored a book on the science of marathon training—however, there’s a bit of a catch: this book was printed through the IAAF (now World Athletics), not a traditional publishing company or printing press. As a result, Canova’s book is extraordinarily rare. I had heard of this book probably a decade ago, but in the intervening years I couldn't find any substantive information on its contents. Until now.

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Elite Marathoning with Renato Canova: The Training of Moses Mosop and Abel Kirui

Renato Canova-coached athlete Moses Mosop winning the Chicago Marathon

Renato Canova is a widely-renown coach of some of the most elite middle and long-distance athletes in the world.  His runners routinely medal at World Championship and Olympic races and place highly at major marathons. 

Unlike many other elite coaches, Renato Canova has no reservations about sharing his training philosophy and the workouts of his athletes.  2011 was a banner year for Canova, as several of his runners won medals at the 2011 world championships, including Abel Kirui, a young runner who won his second marathon World Championship. 

Additionally, Moses Mosop, a long-time Canova runner with sub-27 10k credentials, made his debut marathon in an earthshaking 2:03:06 for second place at the Boston Marathon, then later smashed the 25k and 30k world records at the Prefontaine Classic meet in Eugene, Oregon. 

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Did you know I have a book? Check it out here!