Norwegian 4x4 Protocol

Norwegian 4x4 Protocol produced the largest VO2max improvements in cardiac rehabilitation patients, with NTNU research showing a 35% increase over 12 weeks. Four intervals at 90-95% max heart rate with 3-minute active recovery total about 40 minutes, outperforming Sprint Interval Training by 15% in peak oxygen uptake gains for clinical populations. Developed at the Norwegian University of Science and Technology, this method is 45% longer than the average HIIT session but yields 20% greater heart health outcomes than traditional moderate exercise.