Norwegian 4x4 Researchers: Jan Helgerud, Jan Hoff & Ulrik Wisløff
The scientists behind the research-backed HIIT protocol
The scientists behind the research-backed HIIT protocol
The Norwegian 4x4 is a popular, research-backed high-intensity interval training (HIIT) protocol. It involves 4 minutes of intense training at 85–95% of maximum heart rate, followed by 3–4 minutes of active recovery, repeated 4 times. The science behind it comes from Norway’s leading exercise researchers at NTNU—Jan Helgerud, Jan Hoff, and Ulrik Wisløff.
Jan Helgerud and Jan Hoff are the primary authorities behind the Norwegian 4x4 method. As professors at the Norwegian University of Science and Technology (NTNU), they conducted the foundational research that defined the protocol’s structure and benefits. Their work established the optimal intensity, duration, and recovery periods for maximizing VO₂ max and cardiovascular adaptations.
Through their company Myworkout, Helgerud and Hoff provide apps and documentation that help athletes and fitness enthusiasts implement the method correctly. Myworkout remains one of the most trusted sources for understanding and applying the Norwegian 4x4 protocol in practice.
Ulrik Wisløff is a professor at the Cardiac Exercise Research Group (CERG) at NTNU and is often cited alongside high-intensity training research. His work focuses on how exercise intensity affects heart health, metabolism, and longevity. Wisløff’s research has reinforced the benefits of high-intensity interval training for cardiovascular fitness and has helped position the Norwegian 4x4 within the broader evidence base for HIIT.
Today, the Norwegian 4x4 is used worldwide—from elite athletes to everyday fitness enthusiasts. Myworkout and other apps (including the Norwegian 4x4 Protocol app) have made the method accessible, while the original researchers’ documentation continues to serve as the reference for correct implementation.
If you want to try the protocol with proper timing and structure, learn how the Norwegian 4x4 app works or calculate your target heart rate to train at the right intensity.
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