Estimated read time: 5.3 minutes (about as long as it takes to convince yourself your first mile was controlled. 🤔)

Hey Performance Nerds! Jonah here.

In April, a man ran 1:59 in his marathon debut. Weeks later, a company is selling the lactate gel it says fueled him.

For a century, lactate was the enemy. Now the secret to a sub-2 marathon?

Here's what you'll learn today:

(Augie doesn't worry about his lactate. He just chases the mailman at threshold and recovers by lunch.)

The gel I race with and keep recommending because the formula makes sense: BETA FUEL delivers 40g of carbs per gel through a 1:0.8 maltodextrin-to-fructose ratio.

That ratio is the point. It helps you use multiple carb transporters, push higher intake, and keep the gut calmer when fueling gets serious.

Stryd gives runners power, pacing, and mechanical metrics that can make training decisions clearer when pace and heart rate do not tell the whole story.

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

For years, coaches blamed lactate for the burn. Wrong molecule.

Lactic acid doesn't really circulate in your body. You carry two separate things: hydrogen ions and lactate.

The hydrogen ions bring the burn. The lactate is fuel.

Making lactate actually slows the acid buildup rather than driving it (Robergs, 2004).

So blood lactate is a gauge of how hard you're working, not the source of your fatigue.

Then George Brooks, a Berkeley physiologist, flipped the story with his lactate shuttle (Brooks, 2018).

Lactate made in your fast muscle fibers travels to your heart, brain, and slow fibers. Those tissues burn it on purpose.

In a hard effort, your body can burn through more lactate than glucose for fuel. It even doubles as a training signal.

We got the villain wrong. Lactate was on our side the whole time.

So why bottle it? The pitch is clever.

The pitch, in theory:

Your carbs hit a ceiling. Glucose and fructose crowd through busy doorways in your gut.

Mixing the two sugars spreads the load across separate transporters (Currell and Jeukendrup, 2008).

With gut training, runners can build from 60 to 120 grams an hour.

Lactate uses a third route. It can reach your bloodstream in about five minutes, versus 15 to 30 for carbs.

In theory, that could raise total fuel without crowding the other two routes.

Infusion studies back part of this. Drip lactate into the blood and it can spare your glucose.

The effect flips with intensity. Above your threshold, lactate may help you keep burning carbs for fuel.

Below it, the pitch claims lactate helps you burn more fat. But in people, the reverse can show up.

Raise blood lactate and your fat cells may release less stored fat into your blood (Pedersen, 2024).

That could reduce fat availability. Scientists have proposed a second brake inside muscle, but that pathway is not proven in people yet.

On paper, it's elegant. That's exactly why companies are racing to bottle it.

Elegant on paper runs straight into three walls.

Wall one is dose.

Lactate probably has to reach 10 to 25 grams an hour to matter. Santamadre's gel carries about 5 grams.

That means three or four gels an hour. Older studies used tiny doses and came up empty.

Wall two is your gut.

Lactate comes as salts, so a real dose means a heavy sodium or calcium load.

One team put a small group of men through the dose fifteen different ways (McCarthy, 2024). Most felt sick, some vomited, and their blood lactate barely moved.

Running also pounds the gut harder than cycling does.

Wall three is taste.

Salty and metallic, and rough to stomach hour after hour.

New formulas claim to fix the taste and the gut load. The method is patent-pending and unproven.

So does it work? Not yet.

Ewell (2024) had the only bump, but VO2max and thresholds stayed flat.

Bordoli (2024) and Northgraves (2014) found no time-trial benefit.

One lactate-gel company's webinar leaned on seven riders. Two outliers drove the entire 8% gain.

Ketones followed the same pattern: pro whispers first, published evidence later. Judge the evidence you can see now, not the headline.

These gels could work. Aitor Viribay is one of the metabolism researchers I respect most.

He's also one of the scientists behind them.

But the performance evidence isn't there yet. For most runners, carbs should still come first.

Bottom line: Lactate is fuel. Drinking more of it has not made athletes faster yet.

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: "Why don't endurance runners need to "fat load" before a marathon or ultra the way they carb load?"

Most runners saw the main lesson: runners do not lack stored fat. The limitation is how quickly fat can support race intensity.

The correct answer?

A. Even lean runners already carry far more fat energy than they can use quickly; race limitation is usually carbohydrate availability and intensity, not total fat stored

Even lean runners begin with far more stored fat energy than they can use quickly. Marathon and ultra performance is usually constrained by carbohydrate availability and the rate at which fuel can support the required intensity, not by total fat stored.

Here's how the votes shook out:

A. Even lean runners already carry far more fat energy than they can use quickly; race limitation is usually carbohydrate availability and intensity, not total fat stored: 212 votes, about 92 percent
B. Fat loading works best for ultras, because long races eventually switch almost entirely to fat after glycogen runs out: 11 votes, about 5 percent
C. A high-fat race-week diet raises fat burning enough that gels become optional for most runners: 2 votes, under 1 percent
D. Fat loading mainly helps by adding intramuscular triglycerides, which the body can burn as fast as muscle glycogen: 6 votes, about 3 percent

Total votes: 231

Why B was tempting:

Ultras use more fat, so B is an understandable trap. But runners do not switch almost entirely away from carbohydrate after glycogen runs low. Carbohydrate still helps support race intensity.

One nuance:

Training can improve fat oxidation, but that does not make race-week fat loading useful.

Bottom line?

Prioritize full glycogen stores and a carbohydrate intake plan you have practiced in training.

I opened my Power Duration Curve in PowerCenter this week. My Critical Power read 317 watts, built from my last 90 days of running.

Lactate threshold is a physiology marker. A lab draws blood across a graded test, finding where lactate builds faster than you clear it. Frozen at test day until you rebook.

Critical Power is the boundary between sustainable and unsustainable effort. Stryd models it from your actual runs, the point where the dominant type of fatigue your body experiences changes. Roughly the effort you can hold for about 40 minutes.

Related markers, different jobs. Lactate threshold tracks your blood response. Critical Power models what you can sustain. Different inputs mean the two won't align perfectly, but CP keeps moving with your fitness.

From 317W, my zones fall out on their own:

Why it matters:

This week, feed your Power Duration Curve one short effort and one long, then let Stryd redraw your zones.

Try it on your next run