THE 4 X 4 EXERCISE METHOD The 4x4 aerobic exercise method—also known as 4x4 interval training—has been gaining popularity in gyms and research labs for years, and for good reason. It’s a go-to form of high-intensity interval training (HIIT), loved not just for the serious fitness gains, but also for its flexibility. So, what makes this Scandinavian-born protocol so popular, and why do experts keep coming back to it? What’s the 4x4 Method, Actually? At its core, 4x4 interval training is simple: four bursts of high-intensity aerobic exercise (think 90 to 95% of your maximum heart rate), each lasting four minutes. Between these intervals, you catch your breath with three minutes of active recovery at a gentler 60-70% of your maximum heart rate. Start with a warm-up, finish with a cool-down, and the whole thing takes just 30 to 40 minutes. That’s part of its appeal. You can do it on a treadmill, a stationary bike, or even outdoors. It scales to your fitness level, too, which is why y...