Estimated read time: 4.12 minutes (about as long as Augie stares at me after an easy run, convinced the post-run recovery should include a treat)

Hey Performance Nerds! Jonah here. 🤓

Your VO2max can swing 4 to 5% between two tests on back-to-back days. That's noise, not fitness.

The mistake is building your training around VO2max. The test that actually predicts your next PR is something else entirely.

Here’s what you’ll learn today:

(Augie has never checked his VO2max. He just repeats the same training block: nap, bark, sprint, recover. Honestly, decent periodization.)

The gel I race with: BETA FUEL delivers 40g of carbs per serving through a 1:0.8 maltodextrin-to-fructose ratio.

Marathon Science subscribers get 15% off one-time purchases with code JONAH26.

Stryd gives real-time power so you can keep easy days easy and hard days controlled. This week's full Stryd training tip is below.

See this week's full Stryd training tip at the end of this newsletter.

VO2max, lactate threshold, and running economy are the three things that decide how fast you can run over a distance (Joyner & Coyle, 2008).

Among elite runners, though, threshold and economy separate the fast from the faster more than VO2max alone.

Take two runners with the same VO2max. The one with a better threshold and economy runs a much faster marathon.

Your VO2max opens the door to a fast marathon, but it's only one piece.

And those tests wobble more than you'd expect.

Back-to-back VO2max tests routinely differ by about 4 to 5%. Blood lactate is far noisier, drifting around 27% between tests.

Your lactate threshold can come out very different day to day. It depends on how the lab defines it, how they measure it, and the device they use.

That's established lab methodology, not a scandal. Measurement error, equipment, nutrition, and the day you show up all move the number.

VO2max, lactate threshold, and the rest can swing a lot depending on when and where you measure them.

You'd need a repeatable test in the same lab, read by a coach who knows how to use it.

Short of that, I wouldn't rebuild your training around it.

The thing every fast runner shares isn't a test score. It's accumulated, sustainable training.

World-class distance runners log 130 to 220 km a week, about 80 to 137 miles (Haugen et al., 2022).

They keep most of it easy, built over years.

And this holds for everyday runners too.

In 917 Boston marathoners, more weekly distance, more sessions, and more quality work were associated with faster finishes. That held even after adjusting for age, sex, and experience (DeJong Lempke et al., 2025).

They sustain it through microperiodization. The week is built so hard sessions, easy days, and the long run fit together without wrecking the next session.

Picture high easy volume plus 2 to 3 key quality days. Each one is spaced by enough easy recovery to adapt and repeat (Sandbakk et al., 2025).

The type of quality day (threshold, VO2max, tempo, or even moderate) is secondary. How much hard versus easy work you do differs by sport, not one fixed model.

Your VO2max or lactate number during a workout isn't what to obsess over. Consistency is.

Miss training and VO2max drops anyway. Expect about 3.9% in under a month, roughly 9.4% beyond it (Zheng et al., 2022).

Consistency is what protects the metric in the first place.

The real job of zones, lactate, and power isn't to tell you if that one workout was a success. It's to keep your easy days easy and your hard days controlled, so you can stack weeks.

The test that actually matters has no lab.

It's this: can you finish three to four weeks of training feeling good and ready to go again?

Do that month after month, and you stack years of consistent training.

That repeated, sustainable block is what raises your VO2max, your threshold, and your race result. Not the lab number.

Scaled for a recreational marathoner. This is a pattern, not a prescription.

The pattern: about 5 to 6 run days, 2 key quality days spaced by easy recovery, the rest easy. Keep easy days easy and hard days controlled so you can repeat the week.

Bottom line: Volume you can sustain for years beats the number you chase for a day.

Jonah

Welcome to the prove you're a nerd section. Each week, I ask a question about a common running science myth.

Answer correctly, and you'll be entered into a weekly raffle to win a package of Jonah's favorite supplements.

Last week's poll asked: "A runner has a hot race. What is the typical heat-acclimation plan?"

Most runners knew the main idea: heat tolerance is trained, not improvised. The part that gets missed is that it is not just a race-week hydration trick, and it is not solved by turning every hard session into a sufferfest.

The correct answer?
A. Do 10 to 14 days of repeated heat exposure, usually 60 to 90 minutes of easy to moderate running or controlled heat stress most days

Heat acclimation comes from repeated exposure over a 10-14 day period. The goal is enough heat stress to adapt, not so much that the rest of the training block falls apart.

Here's how the votes shook out:
A. Do 10 to 14 days of repeated heat exposure, usually 60 to 90 minutes of easy to moderate running or controlled heat stress most days - 170 (about 70 percent)
B. Do two very hard workouts in the heat, because the biggest adaptations come from maximal suffering - 3
C. Wait until race week and focus on extra fluids and sodium, because heat tolerance is mostly a hydration problem - 3
D. Start four to six weeks out and move every hard session into the heat, because heat acclimation takes about a month to build - 67 (about 28 percent)
Total votes: 243

The wrong answer that pulled real votes was D, and it is a reasonable trap. Starting early sounds safer. But moving every hard session into the heat adds a lot of stress, and the typical heat-acclimation window is shorter than most runners think.

Bottom line?
If heat is part of race day, train the exposure early enough to adapt, but keep the work controlled enough that the rest of the block survives.

I run all my threshold sessions by power now, ignoring pace and lactate.

Power responds far faster than heart rate or lactate. Heart rate lags the effort by up to a minute.

Power tracks how hard I am working right now.

That speed lets me steer intensity in real time. It also stays steadier than pace, which hills and wind distort.

My Critical Power right now is 317W. That is the boundary where the type of fatigue I feel starts to change.

So I anchor my key sessions just under it, around 90 percent of CP, about 285W. My go-to is 4 by 4 to 6 minutes at 285W, easy jog between reps.

Sitting just below the boundary matters. Fatigue builds more slowly there, so I recover and repeat the session week after week.

Why it matters:

For your next block, find your CP in your Stryd App, target just below it on threshold reps, and hold it by watts.

Try it on your next run