If you choose “Options” on the /power page you can choose one of 3 models and an explanation with reference link appears further down the page in the “Power profile” section:
The default model is:
Estimated FTP is calculated using power curves from FastFitness.Tips and Morton’s 3 parameter critical power model (ref). The algorithm requires just 1 maximal effort of between 180 seconds and 30 minutes.
Essentially it is a generalisation of the 95% of 20m power rule of thumb to all durations from 3 minutes up. This is very much more robust than the other models which require good inputs or you get wild results. If you do have the correct inputs then Mortons 3P will give you a more personalised curve with your own W’ value.
Morton’s 3 parameter critical power model (ref). The algorithm requires 3 maximal efforts, one of 5s, one of 3-5 minutes and another of between 10 and 30 minutes.
Monod & Scherrer’s 2 parameter critical power model (ref). The algorithm requires 2 maximal efforts, one of 3-5 minutes and another of between 10 and 30 minutes.