The 4x4 timer
Four minutes hard, three easy, four times. Full screen, a beep before every change, your own heart rate band, and the session drawing itself as you go.
Your hard minutes
156 to 164beats a minute, from a max of 173 at 50
43 minutes: a 10-minute warm-up (our default, not the trial's), four rounds of 4 hard and 3 easy minutes, a 5-minute cool-down.
What your result means, and what to do next
- The fourth round was hard to finish at the first round's pace. That's the right effort.
- You couldn't finish. Start a little slower next time, or do three rounds and build to four.
- It felt easy. Go faster or steeper in the hard minutes. You should be breathing too hard to talk.
- Do one or two a week. The trial ran 24 sessions over eight weeks. Keep steady cardio on most other days. The week around it
- Retest the same way in 8 to 12 weeks. Same test, same route or same watch. Believe a change of more than 2 to 4 points.
The session behind it
In the 2007 trial, 40 healthy, moderately trained men did one of four programs three times a week for eight weeks, all matched for total work. The group doing four 4-minute efforts at 90 to 95 percent of max heart rate, with 3 minutes at 70 percent between, raised VO2 max 7.2 percent, from 55.5 to 60.4. The two groups doing the same work at a steady pace did not improve significantly, and the heart pumped about 10 percent more blood per beat after the intervals only. These men were already fit, so the trial says more about the session than about how much a beginner gains.
Steady training still builds most of it. Across 28 trials, steady endurance training raised VO2 max 4.9 points and interval training 5.5, so do both: cardio most days and one or two of these a week.
The warm-up and the counter
The warm-up length is ours, not the trial's: 10 minutes by default, 5 for a quick one. The session counter runs to 24 because the trial ran three sessions a week for eight weeks. In Generation 100, people in their 70s did two a week for five years and held their fitness.
On a beta blocker, the timer shows effort numbers instead of beats: about 16 out of 20 for the hard minutes and 13 for the easy ones. Ask your doctor before hard sessions.
4 sources
- Helgerud J and others, Aerobic high-intensity intervals improve VO2max more than moderate training, 2007europepmc.org
- Milanović Z and others, Effectiveness of high-intensity interval training and continuous endurance training for VO2max improvements, 2015europepmc.org
- Stensvold D and others, Effect of exercise training for five years on all cause mortality in older adults (Generation 100), BMJ, 2020pmc.ncbi.nlm.nih.gov
- Tanaka H and others, Age-predicted maximal heart rate revisited, 2001europepmc.org
