What is Norwegian 4x4?
Norwegian 4x4
The Norwegian 4x4 is a high-intensity interval training (HIIT) protocol involving four 4-minute intervals at near-maximal effort, separated by 3-minute recovery periods, used to improve cardiovascular fitness and VO2 max.
How it developed
- Mar 2026 – Tim Ferriss said that doing the Norwegian 4x4 three times a week for 6 months can provide beneficial effects observable for about 5 years afterwards.
- Jun 2026 – Dr. Stephanie Estima noted that in a period of 8 weeks, practitioners were able to increase their VO2 max by 10% in 2 months.
- Jul 2026 – Tommy Wood reported that in a study, the high-intensity interval training group improved their fitness as well as a zone 2 group, but had much better improvements in hypocamp function and maintenance of hypocamp structure on MRI scans.
- Jul 2026 – Tim Ferriss described the Norwegian 4x4 as a type of interval training, reiterating that doing it three times per week for 6 months provided 5 years of benefits.
In the evidence
Every line below is attributed to a named speaker.
A 6-month Norwegian 4x4 HIIT intervention improved hippocampal function and structure more than zone 2 training in older adults, with hippocampal benefits persisting 5 years after the intervention ended.
“That highintensity interval training group, they improved their fitness just as well as the zone 2 group, interestingly, but they had much better improvements in hypocample function and maintenance of hypocample structure and MRI scan.”Tommy Wood · 20 Jul 2026
The Norwegian 4x4 interval protocol increased VO2 max by 10% in 8 weeks in postmenopausal women.
“In a period of 8 weeks, they were able to increase their VO2 max by 10% in 2 months.”Dr. Stephanie Estima · 29 Jun 2026
Norwegian 4x4 interval training done three times per week for six months produces beneficial effects observable for up to five years afterward.
“If you do it I think it's three times a week for 6 months, you can observe the effects, the beneficial effects, for like 5 years afterwards.”Tim Ferriss · 18 Mar 2026
Norwegian 4x4 interval training three times per week for 6 months is associated with roughly 5 years worth of cognitive benefits, per Tim Ferriss citing Tommy Wood.
“Doing something called the Norwegian 4x4, which is a type of interval training. Doing that, I want to say three times per week for 6 months, provided 5 years of benefits, something like that.”Tim Ferriss · 29 Jul 2026