Dr. John Davis just posted a new LT1 calculator based on 5K time. It suggests upper limits for easy runs. Some folks might find it useful. It's here:
https://apps.runningwritings.com/lt1-zone2-calculator/
The data are most reliable for runners with a 5k time between 14:30 and 22:00. He plans to expand the dataset which would help a slower runner like me. He has several other calculators that might be of interest.
I've been running vanilla NSM since mid-January and started using intervals.icu around the same time. For context, I'm 71 years old and have been running regularly since age 60, so my max HR will be lower than someone in his 30s. I run with a chest strap HR monitor. Where I live tends to be hilly so I rely on HR rather than pace for my workouts.
Garmin estimates my lactate threshold at 154 bpm so I've used that for max HR during ST workouts. I ran a hilly 5K race yesterday during which my average HR was 159 and max was 169. Afterword, intervals.icu told me: "Threshold HR +4 to 159 bpm from 98% of 20m at 162 bpm."
Based on this, I plan to update my ST workouts with a 159 bpm upper limit. Does this seem reasonable?
Thanks!