As discussed in the introduction to this challenge (click the link in the Challenge box to the left if you want to see that), underlying the many variations of “HIIT” out there are two basic concepts.
There are Cardio Intervals. I.e, going fast enough for a short period to be uncomfortable/unsustainable, then a period of slower pace to recover, then repeat. And there’s Metabolic Conditioning. That is, doing strength move intervals at a pace and difficulty-level that brings high-intensity benefits of elevated heart rate and amped-up metabolism.
Which to choose? Here’s a point-of-view if you’re mainly a runner, a cyclist, a swimmer or a “cardio machine guy.” That is, if strength work is the “junior partner” in your exercise mix.
In this case, I urge you to bring HIIT into your life by having it be strength-focused, man. Here are three reasons why, with some curated best-of reading to expand on each point.