Deep Dive: Unpacking My Lactate Bike Test With Gordo Byrn

And exposing some mistakes made this year

On Dec. 8th, I did an in-person blood lactate bike test with endurance legend Gordo Byrn.

Gordo was insanely generous with his time during the test and even gave a full video and written report of the results, which you can access HERE.

In this write up, I’m going to share…

1. what is lactate? and why does it matter?

2. my 2 goals going into the test

3. test setup

4. my results, key takeaways and zone application

5. my #1 lesson learned

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1. What Is Lactate? And Why Does It Matter?

Lactate is a byproduct of the body using significant glucose (carbs) for fuel.

When lactate in the blood rises significantly, it means the body has switched from using mostly fat as it’s primary source of fuel to using carbs instead.

Lactate is measured in mmols. A baseline lactate reading will generally be 1.2 to 1.5 mmol.

An initial rise of 0.3 mmol (or higher) OR rising above 2.0 mmol is a sign of 2 things:

1. you’ve switched from fat burning to carb burning

2. you’ve moved from low intensity (Z2) to moderate intensity (Z3)

If I can understand where my lactate jumps (and at what Heart Rate), I can build up my endurance capacity by training below it.

And I can be more dialed with fueling and intensity when I train above it.

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2. My 2 Goals going Into The Test

1. Better understand the top of my Zone 2, so I can avoid drifting over it in training (when I’m not supposed to)

2. Better understand my higher intensity zones, so I can train smarter within them (and get faster)

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3. Test Set Up

Equipment:

• my TT bike

• Garmin HR chest strap

• Wahoo Kickr Core trainer

• Gordo’s Garmin Edge bike computer to control the Kickr (on ERG mode)

• Nova Biomedical Lactate Plus Meter

Test set up:

We started by taking my baseline lactate off the bike (1.5 mmol). Then I hopped on and began riding at 120 WATTS.

We ramped up with 20 WATT steps (controlled via Garmin Edge) and took lactate at the end of each step duration.

Gordo has a great video breaking down test set up HERE.

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4. My Results, 6 Key Takeaways, Zone Application

Charted Results:

Graphed Results:

Cadence Data: 83 avg. RPM

My 6 Key Takeaways:

1. My lactate dropped by 0.4/0.5 once I got warmed up. I see this as a sign that once I got moving (while maintaining very low intensity), my fat burning ramped up. According to this Peter Attia podcast, this is common in well trained athletes.

TAKEAWAY 1: After completing 3 Ironmans, I’ve built a strong aerobic base.

2. My lactate jumped significantly (0.3+ and 0.5+)at the 200W and 220W steps. This aligns with what I’ve felt in training. I have struggled to hold that power steady in long training sessions (3+ hours).

TAKEAWAY 2: This jump indicates my Gray Zone 1 (above Z2) is 200W to 220W. I am not getting much bang for my buck here.

*** More below on me training precisely in this zone earlier this year ***

3. My first deepening of breath happened somewhere between the 180W and 200W steps. This also marked my first rise in lactate (0.3+)

   1. 180W HR max = 127, HR avg = 119

   2. 200W HR max = 136, HR avg = 129

TAKEAWAY 3: My Aerobic Threshold (boarder between Z1/Z2) is around 180W and the Top of my Z2 is around 200W.

Using past data below in Section 5, I think the Top of my Z2 Heart Rate is ~125 bpm.

4. 280 est. FTP (lactate approaching 4.0) is aligned with my 285 Field Test FTP. I think two wildly different tests having very comparable results validates them both.

TAKEAWAY 4: My Heavy Domain is 225W to 250W

We get this using the top of my Gray Zone 1 and Threshold Minus (boarder between Z3/Z4). Training here is how I will get faster.

Standard Heavy Domain lactate reading is ~2.5 to 3.0 and aligns with my results.

5. My lactate jumped 1.1 mmol (3.0 to 4.1) from 260W to 290W as I approached FTP

TAKEAWAY 5: This indicates my Gray Zone 2 as I approach FTP. Gordo charts this at 250W to 285W, which is the top of my Heavy Domain to FTP.

6. Gordo Equation: Severe Domaine = FTP to 6 minute best (per Training Peaks)

TAKEAWAY 6: My Severe Domain is 285W to 325W. When Base Training, this can be capped at 305W.

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Zone Application:

1. My Z1/Z2 boarder is 180W

2. My Z2 ceiling is 200W and mid/high 120s bpm HR (Moderate Domain is below this point)

3. My Gray Zone 1 is 200W to 225W and low 130s bpm HR

4. My Heavy Domain is 225W to 250W and high 130s to mid 150s bpm HR

5. My Gray Zone 2 is 250W to 285W

6. My Severe Domain is 285W to 325W (capped at 305 in Base Training)

BOOM! Kona has never felt more within reach!!! 🌺🔥🪓

Reminder: human physiology is fluid and these are not exact switches.

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2022 Race Results & Field Tests:

1. Ironman Texas (April 23, 2022) * at sea level

178 avg. Power // 194 Normalized Power // 120 avg. HR // 82 RPM

2. Patriot Half Ironman (June 18th, 2022) * at sea level

223 avg. Power // 231 NP // 134 avg. HR // 97 RPM

3. Outdoor Threshold Test (September 3, 2022) * in Boulder

30 minutes // 297 avg. Power // 303 NP // 153 avg. HR // 89 RPM

4. Ironman Florida (November 5, 2022) * at sea level

179 avg. Power // 188 NP // 133 avg. HR // 91 RPM

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5. My #1 Lesson Learned

1. I spent too much time riding in my Gray Zone 1 this year

This is based on my feel out on the road, the results of this test and my Ironman Florida performance.

It was my first year riding with a power meter and I definitely chased WATT averages. After averaging 178W at IM Texas, I wanted 200W. Badly.

I pushed my ~90 minute Z2 rides too hard and probably missed out on some fitness adaptions that could have made me more aerobically fit.

Here are 6 rides from May/June where I rode directly in my Gray Zone 1:

I finished all these rides knowing I would have had to GRIND to hold that effort for a 70.3 bike leg. And I knew I couldn’t hold it for an Ironman.

There is good news though: I reeled this in as the year progressed.

Even though I may have missed out on aerobic fitness riding too hard in May/early June, I did get great tactical practice on the bike that 100% carried over to having my best ride of the year at Patriot Half Ironman.

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Looking Ahead:

I’ll be more disciplined to keep Z2 rides conversational and be more intentional to slot harder efforts within my Heavy Domain.

And I’ll avoid that oh-so-tempting Gray Zone 1!

I feel I just unlocked a ton of opportunity to improve.