My weekly Norwegian 4x4 on the treadmill is one of my favorite ways to improve my cardiovascular fitness.

It’s quick, simple, and one of the most well-known interval methods for improving VO₂ max, which is one of the best markers of cardiovascular fitness.

The structure is simple: 4 minutes of intensity, followed by 3 minutes of recovery, repeated 4 times. In my case, I do high-paced treadmill running for the harder intervals.

And if you’re new to it, you can always ease in with 2 minutes of intensity first and build up from there. The beauty of it is that it doesn’t take long, but it really challenges your heart, lungs, and endurance.