Aerobic Decoupling (also known as Cardiac Decoupling) is a measure for how much your heart rate drifts (known as cardiac drift) over time. To calculate the value, the ratio of power or pace to heart rate of the first and second half of the activity is compared.
For Premium users, this calculation is now available as a time course for a single activity – any sections can also be compared.
The tool is linked at the magic icon in the activity view:
