Your FTP is limited by the ceiling above it. That ceiling is your VO2max — the maximum amount of oxygen your body can process into usable energy. When the ceiling goes up, everything below it has room to follow.
VO2max intervals are the sessions that push that ceiling higher. They're hard. They're uncomfortable. And they're the most efficient way to improve your aerobic capacity in the shortest time.
The Science in 30 Seconds
VO2max represents the maximum rate at which your body can deliver and utilise oxygen during intense exercise. It's determined by three things:
- How much oxygen your lungs can absorb (pulmonary function)
- How much your heart can pump (cardiac output)
- How much your muscles can use (mitochondrial capacity + capillary density)
VO2max intervals work by forcing your body to operate at or near this maximum for sustained periods. The stress signal tells your body to improve all three links in the chain.
The Protocols
The Classic 4x4 (Norwegian Model)
This is the protocol that Professor Seiler's research has validated most extensively.
- 4 minutes at 106-120% FTP (RPE 8-9/10)
- 4 minutes easy spinning recovery
- Repeat 4 times
- Total session: ~40 minutes including warm-up/cool-down
The key: you should barely be able to complete the last rep. If the fourth rep feels manageable, increase the power for next time.
The 5x3 (Short/Sharp)
Better for riders who struggle to maintain focus for 4-minute efforts.
- 3 minutes at 110-125% FTP
- 3 minutes recovery
- Repeat 5 times
The shorter duration allows for slightly higher intensity, targeting VO2max from a different angle.
The 6x5 (Extended)
For advanced riders with a strong base, this protocol provides the most time at VO2max.
- 5 minutes at 105-115% FTP
- 5 minutes recovery
- Repeat 4-6 times (build up over weeks)
This is harder to sustain mentally but provides the longest exposure to high oxygen demand.
How to Execute Them
Pacing is everything. Start 5% below your target power for the first 30 seconds, then settle into your number. Starting too hard means dying in the final minute.
Recovery between reps matters. Keep pedalling during recovery — don't stop. Easy spinning at 40-50% FTP keeps blood flowing and clears lactate faster.
Frequency: 1-2 VO2max sessions per week is enough. More than that and you're accumulating fatigue faster than you're adapting. Allow at least 48 hours between VO2max sessions and any other quality work.
Duration of the VO2max block: 4-8 weeks of consistent VO2max work produces measurable results. After 8 weeks, either move to a different stimulus or take a recovery week before continuing.
When NOT to Do VO2max Intervals
- During your base phase (they compromise the aerobic adaptations you're building)
- When you're fatigued or under-recovered (you won't hit the target power, making the session pointless)
- More than twice per week (diminishing returns + overtraining risk)
- Without an aerobic base (you need the foundation before pushing the ceiling)
Key Takeaways
- VO2max is the ceiling that limits FTP — push it higher and everything improves
- The 4x4 protocol (4min on / 4min off) is the most research-validated
- Target 106-120% FTP depending on interval length
- 1-2 sessions per week for 4-8 weeks produces measurable results
- Start conservatively — if the 4th rep is easy, increase power next time
- Don't do VO2max work during base phase or when under-recovered
- Use our FTP Zone Calculator to find your exact Zone 5 power targets
- If your VO2max is low, read our 7 fixable reasons guide for the full diagnostic
- Recovery between VO2max sessions is critical — allow 48+ hours
- For how VO2max fits into the annual plan, see periodisation
