VO[sub]2[/sub]max is an attribute of the user, not of a particular activity (during which an estimate of the user's VO[sub]2[/sub]max may be taken), so logically pbjorgen could not have been talking about a metric of that type. Training Effect (which is supported on the FR235), perhaps.
when looking at the description on the Polar pages and how it's explained I can't see that it can be anything else.