Level 6 Valued Member
I believe this is the study used. Not sure if it's similar/same as Norway or not...I think this study must be based on the Trondheim Protocol from Norway. The Dept of Sports Science there has been working on 4*4 mins with 3 mins rests for a good number of years, on regular people, and the obese, and has a good number of studies on it.
It's not quite a brutal as it sounds. For the first few weeks you are only doing 1x4 min session, then 2x4 min session, then three min session, then you work up to doing 4x4 mins session, with 3 mins rest.
Even the >90% of max is a little misleading. In the first few weeks, you hit >90% only in the final minute of the 4 mins. In the last few weeks, you only hit >90% of max for the last two mins or each 4 mins interval. Challenging, but doable and sustainable. Not as hard as you might think.
I've done the program in the past for 16 weeks on the treadmill. It's not super arduous. It led to significant gains in my 1 mile time, my 1.5 mile time (per the US Secret Service fitness standards, placing me in the top 'Excellent' category for my age -- FYI, I'm not in the Secret Service). My 5 k time also improved, despite not running for a continuous 5 k for the 16 week period.
One of the key benefits of the program was that people who don't like to exercise enjoyed it, as it felt quick and invigorating, and stuck to it. There was also a two day a week, mild, strength training component.