In addition to the energy systems, “alternates” also takes into account how you address this system based on what training stage you are in. As an example, yesterday I needed to change my 90 min O/U Threshold wo to a 60 minute wo. At the requested PL I could only select Picket Guard-2 as O/Us are typical threshold intervals in SSBI. However, if you look in the library there are options in the threshold category at 60 minutes and the same PL. But they are either pure threshold (i.e. intervals at FTP) or suprathreshold (i.e. intervals slightly above FTP). Depending on your discipline these are more likely to be on your plan during build or specialty.
