Hello and welcome back to the Endurance Lab newsletter.

In this week’s newsletter, we’re going to talk about none other than Josh Kerr’s training leading into his mile world record. If you didn’t know, Josh Kerr is an elite runner who just broke the mile world record in 3:42.66. For context, Josh called this months ago and said that he was going to do it on this day, which makes it even more impressive.

Now, I don’t know Josh’s training entirely, but I put together what I do know from conversations I’ve had with his Brooks Beasts teammates Isaiah Harris and Brandon Miller, and Josh’s YouTube page. I’ll talk a little bit about his training, what I learned from Brandon Miller, and some of the basic physiology behind running a fast mile.

In talking with Brandon Miller, I learned a good bit about the general training philosophy.

First and foremost, they typically do about three workouts per week.

For Brandon, Mondays and Thursdays are easy days. Tuesdays are tempo-type efforts, such as 10 × 1K at threshold pace, while Fridays are more specific sessions. Typically, these involve running at race pace or even faster than race pace.

Sunday is a long run and hills.

What’s especially nice about Josh Kerr is that he documented many of his key workouts on YouTube before his race. Because of that, we have a fairly good picture of his final month leading into his world record.

>1 Month Out

Roughly 5 weeks before his world record attempt, Josh raced an 800m with Brandon Miller, where he ran 1:44 and probably could have run even faster if the race had unfolded differently.

>4 Weeks Out

4 weeks out, he completed one of his key Friday sessions: 4 × 800 meters with six minutes of recovery.

You can think about this as roughly a 1:3 work-to-rest ratio. He ran 2:00 for the first two repetitions before dropping to 1:50 for the final two.

The reason the recovery is so generous is because of the duration and intensity of the repetitions. He’s essentially running half of his race at goal race pace. If you translated this concept to another event, it would be like running 2,500 meters of your goal 5K pace, which is incredibly demanding.

Anytime you prescribe a workout like this, you want the athlete to be fully recovered before the next repetition because the entire purpose is to hit race pace. If you can’t run race pace with full recovery, then the purpose of the workout becomes meaningless.

The first two 800s primarily create pre-fatigue and prepare him to run exceptionally fast when it matters most, during the final two repetitions.

>3 Weeks Out

Three weeks before his world record attempt, Josh completed another key Friday workout consisting of four sets of:

200, 600, 200

All of the repetitions were run at goal mile pace.

He took 90 seconds after the opening 200, 60 seconds after the 600 before the final 200, and then 4:30 between each set, essentially allowing for full recovery.

You can think of these as broken 1Ks at world record pace.

His splits were:

27, 1:24, 26
26, 1:21, 25
25, 1:22, 25
25, 1:20, 25

In practical terms, he’s running roughly 800-meter pace for the 200s and goal mile pace for the 600s. He’s taking approximately a 1:2 work-to-rest ratio for the 800-meter pace portions before giving himself only 60 seconds after the 600 at world record pace and immediately returning to 800-meter pace.

Physiologically, you can think about this as priming the pump to simulate the second half of a mile. He reaches world record pace at the hardest point of the workout before accelerating again at 800-meter pace to spike lactate, then repeats the entire process.

>2 Weeks Out

Two weeks before his race, Josh completed perhaps his most impressive workout: a 1,200-meter time trial at altitude.

Keep in mind that all of these workouts were performed at roughly 5,500 feet.

He ran an incredible 2:42 while finishing with a 51-second final 400.

To me, this was the workout that made me believe the world record was highly likely.

The final 400 meters demonstrates that the opening 800 meters were almost entirely under control aerobically. If you’re capable of closing a hard 1,200 with a 51-second lap at altitude, you’re probably in extraordinary shape.

One Week Out

Now, we don’t fundamentally know whether the timing of every workout shown on YouTube matches the exact timing before his race. However, I highly doubt he completed this time trial one week before his world record attempt.

That simply wouldn’t make much sense, and most coaches probably wouldn’t prescribe something that demanding immediately before the biggest race of the season.

My guess is that his final week consisted of something much simpler, perhaps a few race pace 400s or another light sharpening session.

I could certainly be wrong, but considering the time trial occurred in Albuquerque and the race itself required international travel, it seems unlikely that there was enough time to recover fully from such a demanding effort.

Tuesday Sessions

Unfortunately, we don’t know nearly as much about the Tuesday workouts.

However, we do know that at least one session consisted of six one-mile repeats with one minute of recovery, starting around 4:40 pace and cutting down to roughly 4:20 pace in Albuquerque at altitude.

Based on Brandon Miller’s comments, I suspect many of the remaining Tuesday workouts were relatively simple threshold sessions.

What We Still Don’t Know

There are still several pieces of the puzzle that remain unknown.

-His weekly mileage, which, if I had to guess, was probably somewhere between 60 and 70 miles per week. It may have been as high as 100, but I have a hard time imagining much higher than that.

-His long run distance.

-How many hill sprints he performed. Based on what Brandon Miller described, I suspect these happened at least once per week following his long run and ranged from 30-90 seconds in length.

One Final Observation

One thing many people noticed is that Josh appeared to lose a good bit of weight leading into this race.

I don’t recommend people intentionally lose weight before racing, and I’m not going to comment on whether that’s what happened here.

What I will say is that VO₂ max is a relative measurement, meaning we divide the amount of oxygen you consume by your body weight in kilograms.

For example, suppose someone consumes 6 L of oxygen per minute. We first convert that to milliliters by multiplying by 1,000, giving us 6,000 mL per minute. If that person weighs 220 pounds, or approximately 100 kilograms, their VO₂ max would be:

6,000 ÷ 100 = 60 mL/kg/min

Now suppose they lose just 1 kilogram while maintaining the exact same oxygen consumption.

Their VO₂ max becomes:

6,000 ÷ 99 = 60.6 mL/kg/min

We can take this one step further. Because we have metabolic equations describing the relationship between oxygen consumption and running velocity, we know that roughly a 0.6 mL/kg/min increase in VO₂ max corresponds to approximately a 0.11 mph increase in velocity at VO₂ max.

Put another way, every six-unit increase in VO₂ max corresponds to roughly a 1.1 mph increase in velocity at VO₂ max.

Likewise, losing 2 kilograms, or roughly 4.5 pounds, would theoretically increase VO₂ max by about 1.2 mL/kg/min, corresponding to approximately a 0.2 mph increase in velocity at VO₂ max.

When you’re talking about breaking the world record in the mile, where the margins are incredibly small, even tiny improvements in velocity at VO₂ max can have meaningful effects on race day.

That may help explain why Josh appeared exceptionally lean.

However, it is also why I don’t recommend chasing a so-called “race weight.” Maintaining that level of leanness likely increases injury risk, decreases overall wellness, and is probably not sustainable over long periods of time.

For clarity, I do not recommend intentionally pursuing race weight, as doing so can contribute to longer-term health and performance issues.

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