I’ve posted these in other topics but it’s useful to have them both here.
Here is a link ti Seiler’s paper “Adaptations to aerobic interval training: Interactive effects of exercise intensity and total work duration” which is the research which defines the 4 x 8 minute protocol.
This is the presentation by Prof. Bent Rønnestad which highlights the study into the 2:1 shorter intervals.
Unfortunately the paper isn’t freely available.
Mike