Today I planned to do a 2hr indoor workout. The previous day rode in ERG mode for 2 hrs at a fixed power of 181 W. It was pretty boring. To alleviate the boredom, I thought I could do with a workout that had variable levels of intensity and duration. I had a quick look in my workout library in Training Peaks and couldn’t immediately find anything that fit my requirements. Then I wondered whether I could use AI to design a workout for me 🤔

When I prescribe myself workouts, I use intervals.icu. Their workout builder works perfectly for my software engineer mind. Conveniently, workouts are automatically synced to Garmin. There’s no GUI; workout creation is driven by lines of text. This is what a basic 3-step workout might look like:

- 10m 50-60%
- 20m 70%
- 10m 40-60%

The format is - <duration> <intensity>, duration almost explains itself. Intensity can be a percentage of FTP or zones or ranges thereof e.g., Z1-Z2 or 60-70%

My next step was to find some AI to create my workout. I use Kagi and it comes with an AI assistant. Perfect. The default AI was Claude 3.5 Sonnet. Not sure how GPT 4o would have fared.

The first step is to give the AI some basic background info about how to create an Intervals.icu work:

You are a workout creator for indoor bike workouts. Bike workouts are specified using bullit points, using time in the format of duration followed by h for hours, m for minutes or s for seconds, the second value is percentage of FTP e.g., - 10m 65-75%.

The AI response was:

Claude 3.5 Sonnet I'll help you create indoor bike workouts. I understand you want the format to be: - Duration (using h/m/s) - Intensity (as % of FTP)

Would you like me to create a specific type of workout (endurance, intervals, threshold, etc.) or would you like me to specify the intended duration of the workout? This will help me create a more appropriate training session.

For reference, typical intensity zones for cycling are:

• Recovery: 45-55% FTP
• Endurance: 56-75% FTP
• Tempo: 76-87% FTP
• Threshold: 88-95% FTP
• VO2 Max: 96-105% FTP
• Anaerobic: 106%+ FTP

Please let me know your preferences and I’ll create a structured workout accordingly.

Now to tell it what sort of workout I want:

I want a 2hr workout at an endurance level. My FTP is 272. Total TSS should be no more than 100. Intervals should be of variable length, and variable intensity.

The response was:

Claude 3.5 Sonnet I'll create a 2-hour endurance workout with variable intervals while keeping the TSS under 100. Since your FTP is 272W, I'll focus on the endurance zone (56-75% FTP) with some tempo work mixed in to add variety while maintaining the TSS target.

Workout Structure:

• 10m 55-65% (Warm-up)
• 15m 65-70%
• 8m 75%
• 12m 65%
• 20m 70-75%
• 5m 60% (Recovery)
• 15m 75%
• 10m 65%
• 12m 72%
• 8m 60% (Recovery)
• 10m 75%
• 5m 65%
• 5m 60% (Cool-down)

Total time: 2 hours (120 minutes) Primary intensity: Endurance zone (56-75% FTP) Power ranges:

• 55% = 150W
• 75% = 204W

This workout maintains a predominantly endurance-focused structure with varying intervals to keep engagement while preventing monotony. The intensity changes are gradual to maintain aerobic development, and recovery periods are strategically placed. The TSS should fall between 85-95 depending on how closely you stick to the prescribed power ranges.

That looks pretty good but when I pasted it into intervals.icu I noticed the intensity was slightly higher than I wanted:

Can you reduce the overall intensity from 68% to 65%?

The adjusted workout was perfect. Loaded it into [intervals.icu](https://intervals.icu), it sync’d to Garmin and I used my Garmin Edge 840 to control my trainer.

Claude 3.5 Sonnet I'll adjust the workout to average around 65% FTP instead of 68%, which means working primarily in the 60-70% range with fewer periods at 75%.

Workout Structure:

• 10m 55-65% (Warm-up)
• 15m 60-65%
• 8m 70%
• 12m 65%
• 20m 65-70%
• 5m 60% (Recovery)
• 15m 70%
• 10m 65%
• 12m 65%
• 8m 60% (Recovery)
• 10m 70%
• 5m 65%
• 5m 60% (Cool-down)

Total time: 2 hours (120 minutes) Primary intensity: Lower endurance zone (60-70% FTP) Power ranges:

• 55% = 150W
• 70% = 190W

This revised version maintains the same structure but reduces the overall intensity by:

• Lowering the 75% intervals to 70%
• Reducing some of the 65-70% ranges to 60-65%
• Keeping recovery intervals the same for adequate rest

The TSS will now be lower, approximately 75-85, making it a more moderate endurance-building session.

I see lots of people struggling to set their HR zones on their Garmin watches and this leads to all manner of weird issues. Setting zones should be simple.

First off, what not to do? I would caution against using 220-age to find your max HR. I think that formula may work well for studying large groups of individuals but I suspect doesn’t work well for individuals. Much like BMI.

Max HR or Lactate threshold HR? I think finding max HR is problematic. Max HR will change depending on your training status. If you’re at the end of a heavy block of training, you may not be able to achieve max HR. Finding your max HR isn’t pleasant either. I think it’s better to use LTHR, in my experience, it doesn’t vary much. Most importantly, I think LTHR is more useful, it’s the threshold beyond which your rate of fatigue increases.

Step 1 — determine your LTHR

Joel Friel provides good advice for establishing your LTHR.

To find your LTHR do a 30-minute time trial all by yourself (no training partners and not in a race). Again, it should be done as if it were a race for the entire 30 minutes.

at 10 minutes into the test, click the lap button on your heart rate monitor. When done, look to see what your average heart rate was for the last 20 minutes. That number is an approximation of your LTHR.

This weekend I ran the Leeds Half-Marathon. My average HR for the 85 minutes was 161bpm. I could use that as my LTHR or I could let intervals.icu tell me, which it did. I think either value would work fine.

Step 2 — personalise your zones

Then I use Garmin Connect to set my zones in my device’s user profile.

My zones happen to be:

• Z1 -73%
• Z2 74-86%
• Z3 87-97%
• Z4 98-100%
• Z5 101-

Zone 2 is where I spend most of my training time and is the most important one for me. I did tweak my Z2 range from the defaults. 74-86% of 163 is 120-140bpm and I know I’m still able to breathe easily and have a conversation in this zone.

That’s all there is to it when setting heart rate zones.

Circuito Chico is a ~20km road that is ~20km from downtown Bariloche. It is one of the main attractions in the area and offers spectacular scenery and it’s from there that you can access Colonia Suiza. A picturesque Swiss-style village. Cycling the Circuito Chico is often suggested as the best way to experience it as opposed to driving. My wife and I recently visited Bariloche and completed the Circuito Chico on bikes but it ended up being a day of frustration rather than one of relaxing in a gorgeous location.

Don’t cycle from Bariloche to Circuito Chico! It’s a ~40km round trip from downtown Bariloche and is not worth the time and effort. You might think, like I did, what could ruin a 40km ride near the banks of the nearby lake?

1. The vast majority of bikes available for hire are mountain bikes. The bikes are heavy, the tires are slow MTB tires. A gravel bike would have been ideal. An e-gravel bike would have been better. I didn’t spot either of those along the way.
2. You can’t see much of the lake along the way, so the ride isn’t very interesting.
3. Worse. The road is busy. The good news is that the cars give you space. The bad news is that the buses don’t, they expect you to ride in the dirt. One bus passed me so close that I could touch the side of the bus.

It took us almost 2hrs to cycle 20km to Circuito Chic and by then we felt like we’d had enough. The stiff headwind didn’t help either

My advice would be to drive or grab a public bus to Circuit Chico. Then hire an e-bike at the start point. Circuito Chico is not flat! It has numerous short climbs with some tough gradients. Yes, we had a tailwind on the way back but by then we were too spent to enjoy it.

Check my ride on Strava