IntervalPro
The Norwegian 4x4 Protocol
4 min hard (90-95% max HR), 3 min active recovery, repeated 4 times.
Developed in Norway, this protocol is scientifically proven to significantly improve VO2 max and cardiovascular fitness. It's a highly effective endurance-building workout favored by elite athletes.
- Increases VO2 max by 10-15% in 8-12 weeks
- Improves stroke volume and cardiac output
- Enhances lactate threshold and clearance
- Builds mental toughness and pacing awareness
- Gold standard for improving cardiovascular fitness