Thread by @hybridathlete8

From December 2023 to October 2024, I improved my Zone 2 running pace by ~3:00/mi.

And improved my 5k time from 20:35 to 17:15.

The craziest part?

I did it running less than 15 miles per week!

Here’s how I did it:

In January 2024, I ran 40 mins at an avg pace of 10:49/mi and avg HR of 135.

10 months later, I ran 40 mins at an avg pace of 7:46/mi and avg HR of 136.

Over those 10 months, my resting heart rate dropped from 55 to 45.

And my 5k time improved from 20:35 to 17:15!

First off, let’s talk about how I’m defining Zone 1/2 for me.

My Max HR is 190, and my RHR is ~45.

For me, the upper end of Z2 was ~150 bpm.

Top end of Z1 was ~135bpm.

Here's my total training time (run + bike) by Zone, as you can see, a whole lot of Zone 1:

Here is my weekly running frequency over those 10 months:

January: 1 day (Z2)
February: 1 day (intervals)
March: 1 day (intervals)
April: 0-1 day (Z2)
May: 2 days (1 Z2 + 1 interval)

June: 2 days (1 Z2 + 1 Z3/4)
July: 1 day (Z2 or interval)
August: 2-3 days (2 Z1/2 + 1 interval)
September: 3-4 days (3 Z1/2 + 1 interval)

Weekly mileage: 5-15.

I only ran over 15 mpw six times in this period, and only once above 20.

My weekly average was 7.6 mpw.

And I averaged less than 1 high-intensity running workout per week.

So, how have I improved my aerobic endurance so much with such little running?

-I did a lot of Zone 1 stationary biking.
-I lost ~15 pounds (197 ->182)
-I have good endurance genetics.

If you think Zone 2 feels too slow and easy, wait until you try Zone 1.

This thread will be mostly about Zone 1/2 biking, but I’ll quickly address the genetics and body composition for running.

First, your genetics are what they are.

You may not respond as well as I did to this type of training.

But I still think it's worth a try for many people.

Body Composition

Getting leaner will have a massive impact on your running ability.

More so than almost anything.

The fastest way for most people to improve their running ability is to get leaner.

I'd say at least 1 minute of my improvement was solely due to weight loss.

The best runners in the world are ~8% body fat.

If your goal is to truly maximize your running performance, you need to focus on optimizing your body composition (to a point).

You don't need to be 8%, but getting down to 10-12% will do wonders for your running ability.

And it'll greatly reduce your injury risk.

Next, there are two main reasons I did so much biking and not more running:

1. I was afraid of getting injured.
2. I wanted to be able to still lift heavy 3-4 days per week

Zone 1 biking is very easy to recover from and takes much less out of the legs than running.

At first, especially if you come from a high-intensity background, Zone 1 biking feels like an absolute waste of time that can’t possibly improve your fitness in the slightest.

It will feel way too easy.

The magic of it is that it has most all of the same benefits as Zone 2 training, but the intensity is lower, and therefore, it is far easier to recover from.

Most importantly, it’s much easier to do a high volume of.

Here's the zone breakdown of my biking from this time period:

Especially if you're trying to maintain/gain strength, Z1 training is a true cheat code.

I can do 1-2 hours of Z1 biking, and I feel no negative effects from it when lifting.

It’s crazy.

I still can’t believe it took me 15+ years to figure this out and truly give it a try.

@Alan_Couzens was my initial inspiration for doing more easy work, and @feelthebyrn1's substack has been extremely helpful as well.

@Alan_Couzens @feelthebyrn1 So, what does Z1 biking look like for me?

Then, it was 115-120bpm, now it's a bit higher.

I did the majority of my training on a Concept 2 bike at home or an Echo Bike when I was at work.

And I spend that time mostly reading books on my phone.

It’s pretty awesome.

@Alan_Couzens @feelthebyrn1 And when it's not raining, I get to spend an hour or two outside reading books while also improving my fitness.

It’s a win-win-win.

The only downside to this type of training is that it's time-consuming.

Very time-consuming.

@Alan_Couzens @feelthebyrn1 So, if you have limited time to train, there are better ways to train.

That said, if you have the time and truly want to improve your endurance over the next several years, you must start spending as much time as possible doing Z1 (and Z2) training.

@Alan_Couzens @feelthebyrn1 Biking vs Running HR Zones

My biking HR zones are about 10% lower than my running HR zones.

If you haven't biked much, yours probably are as well.

@Alan_Couzens @feelthebyrn1 During this period, my top-end Z2 on the bike was ~135bpm, and my top-end Z1 was ~120.

For Z2 runs, I targeted 140-150, and for Z2 bikes (which I hardly ever did), I would target 130-135 bpm.

For Z1 runs, I targeted 125-135bpm, and for Z1 bikes, I targeted 115-120bpm.

@Alan_Couzens @feelthebyrn1 Here is what my Z1 bike training looked like over those 10 months:

January: None
February: 3-4x 30-60 mins
March: 2-3x 45-60 mins + 1x90 mins
April: 2-3x 45-60 mins + 1x90 mins
May: 2-3x 45-75 mins + 1x90-120 mins
June: 2-3x 40-60 mins, 1x75+ mins

@Alan_Couzens @feelthebyrn1 July: 1-2x 40-60, 1x60+
August: 2-3x45-60 mins, 1x 75+ mins
September: 2x 45-60 min, 2x75+ mins

Again, 90%+ rides were done at 115-120bpm, with a few in the mid-120s.

For the most part, I averaged 3 hours per week on the bike, some weeks more, some weeks less.

@Alan_Couzens @feelthebyrn1 This thread has been all about the benefits of low-intensity training.

It's awesome, and most people need more low-intensity than they do high-intensity.

But it's just as important that you do high-intensity work if you want to maximize your running ability.

@Alan_Couzens @feelthebyrn1 For me, 1 day per week was plenty during that period and given my total training load.

The biggest key is to keep the low intensity low and the high intensity high.

If you go too hard on the easy stuff, you won't be able to go hard enough on the hard stuff.

Again, if you’re someone who is looking to improve your aerobic endurance while simultaneously lifting weights, training jiu jitsu, doing CrossFit, or doing whatever, Z1 is the way to go.

To start, I’d shoot for 2-3 hrs/wk.

Min of 30 mins/session, and try to get at least 1 session of 45+ mins.

@Alan_Couzens @feelthebyrn1 After a few months, try to increase the minimum session to 45 mins and the long session to 75 mins+.

Currently (August 2025), I shoot for ~7-8 hours of Z1/Z2 per week:

-2-3 x60+ min on the bike
-1 x 120+ mins on the bike
-1 easy run of 45-60 mins
-1 long run of 60-90 mins

@Alan_Couzens @feelthebyrn1 This style of training is also great for those who:
-want to get into hybrid-style training
-love running
-want to improve their running
-have historically had issues with getting injured when increasing their running volume
-weigh more than the average runner
-are new to running

@Alan_Couzens @feelthebyrn1 Spending more time biking (or whatever low-impact modality you choose) is a great way to build your aerobic base while you slowly increase your running mileage.

If you don't like biking, you can walk, elliptical, swim, etc.

Just keep the intensity low.

@Alan_Couzens @feelthebyrn1 This style of training improved my 5k time from 20:35 (December 23rd) to 17:15 (October 23rd).

It also allowed me to run a 1:26 half-marathon (June 22nd) off of ~15 mpw.

And a 5:05 mile (July 17th) with zero mile-specific training.

@Alan_Couzens @feelthebyrn1 It has also allowed me to lift heavy 3-4 days per week and maintain the strength to total (bench + squat + deadlift) 1200 pounds.

My last total (June 2024) was 290# BP, 400# BS, and 510# DL.

*Currently about 10% weaker on all lifts due to greatly reduced lifting frequency. 😂

@Alan_Couzens @feelthebyrn1 Lastly, here's a comparison between a January, April, and September Z2 run:

First, they are on the same exact running trails in fairly similar weather.

My goal with all was to keep my HR 140-145.

@Alan_Couzens @feelthebyrn1 As you can see, huge difference.

Mile 1 pace is ~1 min faster each run, but HR is significantly lower each time.

And I'm running 7:30 pace the last 3 miles at ~143 HR in Sept and 9:30+ at 149 HR in April.

Pretty crazy.

@Alan_Couzens @feelthebyrn1 Lastly, a couple of quick disclaimers:
-I’m not saying everyone should train this way.
-I’m not saying Zone 1 biking is superior to running for improving running performance.
-I’m not saying Zone 3 is bad and should be avoided.

For my goals then, keeping almost all of my training either in Z1/2 or in Z4/5 worked very well.

And keeping the majority of my low-intensity training on the bike allowed me to continue to lift heavy and stay strong.

But goals change.

I'm currently doing mostly Z1 for easy and mostly Z3/low Z4 for high intensity.

@Alan_Couzens @feelthebyrn1 Although I had great results, if I could go back in time, I would do it a bit differently.

In short, I would run more frequently (3-4 days per week) from the start, BUT much slower and much shorter at first.

More walk/runs and more very slow running to let my body adapt.

@Alan_Couzens @feelthebyrn1 Well, if you're still reading, I hope my story has convinced you lose some weight and to give Z1 training a try!

Please drop any comments or questions below!