Computed activity fields

Yes both of those are easy. I started with ActivityJsData from the server side data model and then looked at JsHRCurve and JsPowerCurve.

Best 20m power:

{
  icu.powerCurve.getWatts(20 * 60)
}

Best 20m HR:

{
  icu.hrCurve.getBpm(20 * 60)
}