Explained by the originators of the Norwegian Protocol
4x4 Strength Training is a simple yet effective method for building muscle strength, function, and resilience. It’s based on the principle of doing:
- 4 repetitions
- in 4 sets
- using a heavy load
This approach targets the nervous system as much as the muscles. It's designed to challenge your brain to send stronger signals to your muscles, triggering adaptation — in both strength and coordination.
The method is recommended and scientifically validated by Professors Jan Hoff and Jan Helgerud, creators of the Myworkout app and world-leading experts in exercise physiology. With over 200 peer-reviewed studies, their research shows that 4x4 strength can increase muscle force by 2% per session — with just one focused exercise per session.
✅ Efficient: 2% stronger with just one exercise per session.
🦵 Functional: Improve walking, balance, and strength in daily life
🧠 Brain-powered: Trains your nervous system to send stronger signals
🧓 Age-friendly: It's never to late to start, and it helps you stay mobile and independent as you get older.
🏃 Performance-enhancing: Boosts running economy and mechanical efficiency
🩺 Clinically tested: Proven as an effective treatment for Parkinson’s, stroke, COPD, multiple sclerosis, Hypertension, and both pre- and post-surgical recovery.
Muscle strength plays a vital role in disease prevention of several inactivity-related diseases, including type 2 diabetes and certain cancers.
We recommend focusing on major muscle groups — especially the legs — because function matters. Whether you're training for performance (like improving running economy) or simply want to stay steady and strong as you age, leg strength is key. Staying on your feet is what keeps you out of the sick bed — it’s that simple.
Prioritize exercises like:
Legs: Leg press, squats, one-legged squats
Back: Pull-ups or rows
Chest & shoulders: Bench press or push-ups
Muscle strength is primarily dependent on an active nervous system. The brain must be challenged to produce powerful nerve signals that are transmitted to the muscle, which adapts to the demands of great resistance by changing the composition and size of the muscles. Heavy loads and mobilization of power are crucial to create change.
You don’t need endless variations. Just target one exercise per large muscle group (like legpress for the legs), train heavy, and repeat consistently.
Reps: 4
Sets: 4
Intensity: High enough to be challenging but with control and good form
If your goal is health and function, one well-chosen exercise is enough.
You don’t need a complicated routine or endless variations. Just choose one effective exercise per large muscle group — that’s enough to trigger meaningful strength gains. Keep it simple. Train heavy. Repeat consistently.
Each session can improve your strength by up to 2%, which becomes noticeable over time. Not a long time — but don’t expect more than that in a single workout. Pushing beyond won’t give you extra gain, and can even reduce recovery quality.
Rest is a critical part of the 4x4 principle — both in intervals and in strength. It allows your muscles and nervous system to recharge, especially for generating maximal force.
4x4 Strength and 4x4 Intervals together give you the ideal balance of cardiovascular capacity and muscular strength — a proven formula for performance, prevention, and longevity.
Combining these two pillars of training lowers blood pressure: Combined 4x4 intervals and strength training can reduce hypertension by up to 18/12 mm Hg, while improving VO₂max, leg strength, and overall cardiovascular health.
This is quite simply, the Fountain of Youth.
Track your progress in the Myworkout app
Why does strength matter so much as you get older? Because function is everything. Your ability to:
- Get up from a chair
- Climb stairs
- Catch your balance after a stumble
...all depend on strong leg muscles. Lose strength — and you risk losing independence.
4x4 Strength Training focuses on functional muscles that support daily life. By targeting large muscle groups (especially in the legs) with heavy resistance, your body becomes more efficient, resilient, and capable.
Did you know strength training improves both your muscles and your brain function When you lift heavy, your nervous system is forced to activate more muscle fibers by sending stronger, faster signals from the brain to your muscles. This is called efferent neural drive, and it's key to both movement and coordination. Research on patients with conditions like Parkinson’s, stroke, and multiple sclerosis — shows that maximal strength training improves neural efficiency. In practice, this means better balance, faster reaction times, and more confident movement.
The 4x4 interval method is one of the foundational pillars of our app, Myworkout GO, and it serves as a tool to improve your quality of life and measure your health status with scientific accuracy.
The Myworkout technology and its precision in measuring VO2max and biological age comes from robust scientific research. The published study "Prediction of VO2max from Submaximal Exercise using the smartphone application Myworkout GO" by Jan Helgerud, Håvard Haglo, and Jan Hoff, demonstrated the app's accuracy.
The conclusion that Myworkout GO accurately calculates VO2max and is a practical tool for health risk estimation, potentially increasing physical activity and improving exercise habits in the general population.
With the published study “Smartphone-Assisted High-Intensity Interval Training in Inflammatory Rheumatic Disease Patients - Randomized Controlled Trial” by Jan Helgerud, Håvard Haglo, Eivind Wang, and Jan Hoff, demonstrated that Myworkout GO has the same follow-up effect as a therapist.
The app estimates VO2max and biological age by assessing your performance during a standard 4x4-minute high-intensity interval session.
The app's margin of error is 4.5%, which means that it is very close to the direct measurement of VO2max. Furthermore, the app compares your VO2max and biological age to the average values for your gender and age group, and shows you how you can improve them over time. This approach is safer and more accessible than direct measurements, even for those with health concerns.
When the app knows your VO2max, it can subsequently understand when you're in the right intensity zone for all types of activities. We call this zone HIT (high-intensity training).
You earn HIT points by staying in the correct intensity zone during the intervals, which is based on your capacity and heart rate. You only need 32 HIT points per week to keep your streak, making it an achievable goal for everyone. The app also tracks your progress, rewards your achievements, and motivates you to stay consistent and challenge yourself.
By engaging in our methods, we assure you that you can achieve a biological age of 20 even as your physiological age approaches 70.
For outdoor exercise, the app uses the sensors in the smartphone, GPS and DEM-technology to capture barometer data to calculate your speed and incline. Indoors, on a treadmill, it uses the recorded incline and speed. For devices like rowing machines, bikes, and ellipticals, you can enter your watt level.
No special equipment is needed—just a smartphone. However, if you already use wearables, you can integrate them with our app.
Want to experience this for yourself? Start with just one 4x4 strength session per week.
Choose a leg exercise, go heavy, and track it in the Myworkout app.
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