Norwegian 4x4 Protocol

Norwegian 4x4 HIIT Timer — Interval Training & VO2 Max BOOST VO2 MAX WITH NORWEGIAN 4X4 PROTOCOL WORKOUTS Train smarter with the Norwegian 4x4 protocol, one of the most studied HIIT methods for improving cardiovascular performance and endurance. A precise, distraction-free timer guides every interval so you can focus on the effort. KEY FEATURES: - Norwegian 4x4 Timer - Precision 4min work / 3min rest cycles - Heart Rate Training - Track 90-95% max HR zones - VO2 Max Improvement - Scientifica