VO2 Max Protocol

For you, I’d make the incline treadmill the default, not the bike and definitely not flat-out running.

The original Helgerud study used interval running: 4 × 4 minutes at 90–95% HRmax, separated by 3 minutes of active recovery at ~70% HRmax, 3×/week for 8 weeks. But 4×4 also works very well on a cycle ergometer; studies have successfully produced the intended 85–95% HRmax stimulus that way. Recent cross-training evidence also doesn’t show a clear large disadvantage of cycling versus running for VO₂max improvement, although running remains more specific to running performance.

What I’d have you do

Incline treadmill Norwegian 4×4, 1×/week initially:

1. 10 min warm-up — easy walk/jog, progressively increasing effort.
2. 4 min hard — incline + speed sufficient to get you toward the high aerobic range.
3. 3 min easy — keep walking, don’t stop.
4. Repeat that 4 times.
5. 5–10 min cooldown.

Total = about 40 minutes, but only 16 minutes are hard.