4x4 Interval Training
The 4x4, also called the Norwegian 4x4, is four 4-minute intervals at a hard effort of about 85 to 95% of your max heart rate, each followed by about 3 minutes of easy active recovery, with a warmup before and a cooldown after. It is one of the most studied ways to raise your VO2 max.
4x4 at a glance
- Format
- 4 x 4 min hard / 3 min easy
- Work intensity
- 85 to 95% max HR
- Recovery
- 60 to 70% max HR
- Total time
- about 40 minutes incl. warmup and cooldown
- Frequency
- 1 to 3 hard sessions per week
- Trains
- VO2 max and aerobic power
What 4x4 interval training is
4x4 interval training is a high-intensity aerobic workout built around four hard intervals of 4 minutes each. During each interval you work near the top of your aerobic range, around 85 to 95% of your max heart rate, which feels hard but is sustainable for the full 4 minutes. Between intervals you drop back to easy active recovery, roughly 60 to 70% of max heart rate, for about 3 minutes so you can recover enough to attack the next one.
The point of the long, near-maximal intervals is to spend real time with your heart and lungs working close to their limit. That is the part of the session that drives the adaptation. The recoveries are not rest for the sake of rest; they let you keep the work intervals genuinely hard rather than fading into a steady, moderate slog.
How to do a 4x4 session
- Warm up. About 10 minutes of easy effort to raise your heart rate gradually and get ready to work.
- Interval 1. 4 minutes hard at 85 to 95% of your max heart rate. It should feel like you could not hold this pace for much longer than the interval.
- Recover. About 3 minutes easy at 60 to 70% of max heart rate. Keep moving; do not stop completely.
- Repeat for 4 intervals. Alternate hard and easy until you have done all four 4-minute work intervals with a recovery after each of the first three.
- Cool down. A few minutes of easy effort to bring your heart rate back down.
One thing to expect: heart rate lags behind effort. In the first minute of a hard interval your number will look lower than the work feels, because it takes time for your heart rate to climb. Trust the effort early in the interval and let the number catch up, rather than pushing too hard just to hit a target on the screen.
Why it works (the evidence)
The 4x4 format is popular because it reliably improves VO2 max, the maximum rate at which your body can use oxygen and a strong marker of aerobic fitness. Research on long, near-maximal intervals, including work by Helgerud and colleagues in 2007 and Wisloff and colleagues in 2007, found that 4x4 style training produced larger gains in VO2 max than steadier, moderate continuous exercise of similar or greater volume.
The practical takeaway is measured but real: spending time close to your aerobic ceiling is an effective way to raise it. Individual results vary with your starting fitness, how consistent you are, and how hard you actually work the intervals, so treat the 4x4 as a proven tool rather than a guarantee of a specific number.
How often should you do 4x4 intervals
For most people, 1 to 3 hard 4x4 sessions per week is the right range. One session a week is enough to make progress if you are also doing other training; two to three is a strong dose if you recover well. Doing hard intervals every day is usually counterproductive, because the quality of each session drops when you are not recovered.
Fill the rest of your week with easier aerobic work at a conversational pace. This polarized idea, a small amount of genuinely hard work plus a larger base of genuinely easy work, lets you hit the intervals hard on the days that matter while still building aerobic volume the rest of the time.
4x4 interval training for beginners
If you are new to high-intensity intervals, you do not have to do the full four straight away. Start with 2 to 3 intervals and build up to four over a few weeks as the effort starts to feel more manageable. You can also begin at the lower end of the hard range and work toward 90% and above as you adapt.
Focus on effort rather than chasing an exact heart-rate number, especially early on. The intervals should feel hard and leave you breathing heavily, but you should be able to complete all of them. Build gradually, give yourself easy days in between, and stop if anything feels wrong.
Make it easier to run with Ramp4x4
Ramp4x4 is a free Apple Watch-first app that sets up all of the phases for you, calculates your target zones from your heart rate, and cues each transition with haptics on your wrist. You feel when to push and when to ease off, so you can keep your eyes up and just train instead of watching a clock and counting intervals in your head.
Keep going
Run your 4x4 intervals with Ramp4x4
Ramp4x4 is a free guided Norwegian 4x4 timer for iPhone and Apple Watch. It builds every phase, calculates your target zones, cues each transition with haptics, shows live heart-rate feedback, and tracks your progress so you can focus on the work.
4x4 interval training FAQ
What does 4x4 interval training mean?
4x4 interval training means four 4-minute intervals at a hard effort, around 85 to 95% of your max heart rate, each followed by about 3 minutes of easy active recovery. You add a warmup before the first interval and a cooldown after the last one. It is also known as the Norwegian 4x4.
How long is a 4x4 workout?
A full 4x4 session is about 40 minutes. That is roughly 10 minutes of warmup, four 4-minute hard intervals with three 3-minute recoveries between them, and a few minutes of cooldown. The four hard intervals themselves total 16 minutes.
How many times a week should I do 4x4 intervals?
For most people, 1 to 3 hard 4x4 sessions per week is plenty. Keep the rest of your week as easier aerobic work so you can recover and still push hard on interval days. Even one quality 4x4 session a week can raise VO2 max over time.
References
- Helgerud J, Hoydal K, Wang E, et al. Aerobic high-intensity intervals improve VO2 max more than moderate training. Medicine and Science in Sports and Exercise. 2007;39(4):665 to 671.
- Wisloff U, Stoylen A, Loennechen JP, et al. Superior cardiovascular effect of aerobic interval training versus moderate continuous training in heart failure patients. Circulation. 2007;115(24):3086 to 3094.