Here is some info from David T on how that chart is constructed:
Each ride has a power vs HR curve created by breaking the ride up into 1 minute segments, adjusting for HR lag and calculating average power and HR for each segments. These are the data points used for the decoupling related charts on the activity power page. Only segments with 100% moving time are kept.
The traces for the comparison chart are created by bucketing the power-HR segments for all matching activities into power buckets and averaging the HR.
Here is a chart showing my current z2-z3 border (7 zone model: endurance-tempo) and comparison to previous years:
notes, starting from left curve to right:
- 2019 was a year with detraining from May-August, followed by TR traditional base 1 and 2 and finishing with an attempt at polarized. Laid the foundation for 2020.
- 2018 was a mix of TR SSB early in the year, with outdoor riding and a short block of TR’s traditional base in Sept/Oct
- 2020 transitioned to more aerobic development
- 2021 continued the aerobic development
- 2017 was peak fitness with a lot of work in middle zone and anaerobic capacity, starts diverging from 2020-2021 around 82% HRmax
Will be interesting to compare once a full year of 2021 data is available.