Boost your VO2 Max and fitness with the N4x4 app. The Norwegian 4x4 is the best High Intensity Interval Training (HIIT) protocol to increase your VO2 Max. It has nothing to do with cars. :-) This app is set and forget. You press start when your training session begins, and you don't need to mess around with timers until you're done. It will give you visual and audible indications at the start of each high intensity and rest interval.

This app helps you increase your VO2 Max – a key metric for longevity and cardiovascular health. With customizable settings for both beginners and advanced users, N4x4 guides you through:

• 5-minute warm-up
• 4 rounds of 4-minute high-intensity intervals with 3-minute recovery

The benefits of an increased VO2 Max have been confirmed by experts like Dr. Peter Attia and Dr. Rhonda Patrick on their respective podcasts (no association with this app). 

This no-frills app is completely free, with no sign-ups, ads, or in-app purchases. Start building a stronger heart today.