within the research, how is "per week" consistently defined?

I have always assumed it is Monday to Sunday as a 7 day calendar week. However, a non-specific twice per week, could also be a 7 day rolling period from when a muscle or movement was last performed.

A-rest-B-rest-A-rest-rest

B-rest-A-rest-B-rest-rest

A-B-rest-A-B-rest-rest

A-B-rest-A-B-rest-rest

Both of those scenarios could be 2x per week from a 7 day rolling week. They could also be viewed as 2x per calendar week vs 1.5 per calendar week.

edit - the pelland meta doesn't as far as i can see on a mobile, say how exactly it decides frequency per week. there are fractional numbers implied on this graph. how are they being worked out?