Four-minute bursts of effort could help you build cardiovascular fitness without spending hours on the treadmill. What if four minutes of hard running could do more for your stamina than a long, comfortable jog? That is the thinking behind the Norwegian 4×4, an interval-training method designed to challenge the heart and lungs in a surprisingly … Continue reading The Norwegian 4×4 Workout: Can 40 Minutes Help Improve Your Stamina?