What is the Norwegian 4x4?
The 4x4 is a high-intensity interval workout developed and tested by the exercise research group at the Norwegian University of Science and Technology (NTNU) in Trondheim. It became famous because it improves VO2 max, one of the strongest markers of heart health and longevity, in about 40 minutes:
| Part | Time | Intensity |
|---|---|---|
| Warm-up | 10 min | 60–70 % of max heart rate |
| Interval × 4 | 4 min each | 85–95 % of max heart rate |
| Active recovery × 3 | 3 min each | 60–70 % (easy jog or walk) |
| Cool-down | 5 min | 60–70 % |
Heart rate lags behind effort, so it is normal to take 1–2 minutes of each interval to reach the target. Aim to be at about 90 % by the end of each interval: hard, but steady enough to hold for the full four minutes.
Norwegian 4x4 heart rate chart by age
Estimated with the Tanaka formula (maximum heart rate = 208 − 0.7 × age). If you know your real maximum, use the calculator instead.
| Age | Max HR | Intervals (85–95 %) | Recovery and warm-up (60–70 %) |
|---|---|---|---|
| 20 | 194 bpm | 165–184 bpm | 116–136 bpm |
| 25 | 190 bpm | 162–181 bpm | 114–133 bpm |
| 30 | 187 bpm | 159–178 bpm | 112–131 bpm |
| 35 | 184 bpm | 156–174 bpm | 110–128 bpm |
| 40 | 180 bpm | 153–171 bpm | 108–126 bpm |
| 45 | 176 bpm | 150–168 bpm | 106–124 bpm |
| 50 | 173 bpm | 147–164 bpm | 104–121 bpm |
| 55 | 170 bpm | 144–161 bpm | 102–119 bpm |
| 60 | 166 bpm | 141–158 bpm | 100–116 bpm |
| 65 | 162 bpm | 138–154 bpm | 98–114 bpm |
| 70 | 159 bpm | 135–151 bpm | 95–111 bpm |
| 75 | 156 bpm | 132–148 bpm | 93–109 bpm |
| 80 | 152 bpm | 129–144 bpm | 91–106 bpm |
What the research shows
In the study that made the protocol famous, 40 moderately trained men trained three times a week for eight weeks with one of four programmes matched for total work. The 4 × 4-minute intervals raised VO2 max by 7.2 % and the heart's stroke volume by about 10 %, while long slow running (70 % of max heart rate) and threshold running (85 %) did not raise VO2 max significantly (Helgerud et al., 2007). NTNU's researchers have since used the same format in patients with heart disease and in older adults, and recommend 2–3 sessions a week to improve fitness.
Running, treadmill, bike or rower
- Running: the classic version. Hills help: reaching a high heart rate is easier uphill and gentler on the joints.
- Treadmill: set an incline of 3–6 % so you can hit the target heart rate at a manageable speed. The calculator shows speeds for flat and 5 % incline.
- Walking uphill: a steep treadmill incline at brisk walking speed works well for beginners and older adults.
- Bike, rower, ski erg: use the same heart-rate targets; your maximum may be 5–10 beats lower than when running.
Check with your doctor first if you have a heart condition, high blood pressure that is not controlled, or have been inactive for a long time. Stop if you feel chest pain, dizziness or unusual breathlessness.
- Helgerud J, Høydal K, Wang E, Karlsen T, Berg P, Bjerkaas M, et al. (2007). Aerobic high-intensity intervals improve VO2max more than moderate training. Medicine & Science in Sports & Exercise 39(4): 665–671.
- NTNU Cardiac Exercise Research Group (CERG). Exercise advice and 4x4 protocol — ntnu.edu/cerg/advice.
- Tanaka H, Monahan KD, Seals DR (2001). Age-predicted maximal heart rate revisited. Journal of the American College of Cardiology 37: 153–156. Gulati M et al. (2010), Circulation 122: 130–137.
- Pace estimates use Daniels' VDOT equivalents and the ACSM running equation for incline; they are starting points, and heart rate is the target. Last reviewed October 2026.
Last reviewed: September 2026 · Health disclaimer