Get started with Norwegian 4x4 interval training. Norwegian 4x4 Protocol: Boreas makes it easy to get started with the Norwegian 4x4 protocol. Just select warm-up and cooldown duration, and the app handles the rest. You can connect an Apple Watch to track your heart rate and calories. The app supports voice guidance to let you know when the interval is about to end and when the next interval starts. Features: • Perform Norwegian 4x4 workouts. • Know when the next interval starts while the ap