Admittedly I skimmed through it with a preconceived notion, but the research seems to by convenience target endurance runners, but I don't see where it has to be specifically running, or endurance. Why not interval runners, bikers, swimmers, rowers, Tabata interval trainers, any aerobic training?

Specifically since research I've read suggests that VO2 improvments is more efficient with interval training than with endurance training [*].

https://www.ncbi.nlm.nih.gov/pubmed/26243014