VO2 Max 4x4 — Free Zwift Workout
(.zwo Download)
Four 4-minute reps at 110-115% FTP with 4 minutes easy between. The Norwegian 4x4 protocol — the engine-builder for crit and road-race fitness.
Built by Jim Camut. JB Cycling Academy 2004–09 · PCS-verified · Cyclingnews diarist alumnus.
Where are you in your riding?
Trains consistently — doesn't race
What do you want from this workout?
110–120% FTP — engine-builder intervals
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Free .zwo file. Drop it in your Zwift workouts folder — it shows up under Custom Workouts the next time you launch the app.
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VO2 Max 4x4: prescription + science
Four 4-minute reps at 110–115% FTP with equal recovery — the Norwegian engine-builder. Here's why long VO2 reps raise your ceiling faster than steady riding ever will.
Why 4×4 works
Aerobic high-intensity intervals near 90–95% of max heart rate raise VO2 max more than the same time spent at moderate intensity [1]. Four-minute reps are long enough to drive oxygen uptake to its ceiling and hold it there — which is where the adaptation happens.
Why 4 minutes, not 8
Time near VO2 max is the currency, and intensity trades off against rep duration — shorter-harder and longer-easier reps can deliver a similar dose [2]. Four minutes at 110–115% FTP is the sweet spot for most riders: hard enough to pin VO2, repeatable enough to land four quality reps.
Even inside the work interval, varying the power with short surges can push more time above 90% VO2 max than holding a flat wattage [3] — a refinement once you've mastered the steady version.
How to use it
One VO2 session a week is enough when you're also riding easy volume. The recoveries are easy on purpose — the 4 minutes between reps clears fatigue so the next rep is high quality, not a second-rate effort.
Peer-reviewed sources
- 01Helgerud et al. 2007. Aerobic high-intensity intervals improve VO2max more than moderate training. Medicine & Science in Sports & Exercise, 2007.
- 02Seiler et al. 2013. Adaptations to aerobic interval training: interactive effects of exercise intensity and total work duration. Scandinavian Journal of Medicine & Science in Sports, 2013.
- 03Bossi et al. 2020. Optimizing Interval Training Through Power-Output Variation Within the Work Intervals. International Journal of Sports Physiology and Performance, 2020.
VO2 Max 4x4: common questions
What power should a VO2 4×4 be?
Around 110–115% of FTP — a hard, sustainable 4-minute climb effort (about 9/10). The generator sets the watts from the FTP you enter.
How many VO2 sessions per week?
One is plenty for most riders. Two only in a dedicated VO2 block, and only if your easy volume is high enough to recover between them.
4×4 vs 30/30s — which should I do?
4×4 is the bigger single-rep stimulus and a classic ceiling-raiser; 30/30s let you bank more total time near VO2 max with less rep-to-rep breakdown. Rotate them rather than grinding one.
Why are the recoveries so easy?
Between long reps your VO2 drops regardless, so the recovery's only job is to clear fatigue for the next rep. Riding it hard just steals quality from the reps that matter.
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