Norwegian 4x4 vs HIIT | Why Some Athletes Get SLOWER From Interval Training
Norwegian 4x4 and HIIT both improve VO2max, but there's a second adaptation hiding in these intervals that can actually decrease endurance performance. It's the glycolytic training stimulus, and most coaches completely miss it.
Norwegian 4x4 and HIIT both improve VO2max — but there's a second adaptation hiding in these intervals that can actually decrease endurance performance. It's the glycolytic training stimulus, and most coaches completely miss it.
Sebastian Weber (INSCYD founder, WorldTour cycling coach, 9x World Championship titles) explains why two athletes with the same VO2max can have completely opposite responses to the same interval session — and how VLamax (glycolytic power) decides everything.
What you'll learn:
- Why HIIT can increase VLamax in endurance athletes — and why that tanks threshold, fat burning, and race performance
- Why Norwegian 4x4 is glycolytically "safe" for some athletes but risky for others
- The 10% VLamax utilization benchmark: the line between building and destroying glycolytic power
- How to prescribe intervals based on %VLamax (not threshold) to control BOTH the aerobic and glycolytic stimulus
- The Training Zones Builder: how to set VLamax as the constraint and optimize duration for VO2max gains
📖 Read the full article: https://inscyd.com/article/hiit-and-norwegian/
CHAPTERS: 0:00 — Introduction 0:14 — HIIT 40/20: Glycolytic Stimulus for Sprinter vs Endurance Athletes 2:17 — The 10% VLamax Benchmark Explained 4:25 — Norwegian 4x4: Why It Works for Some and Not Others 6:40 — Why This Explains Norwegian Training's Origin 8:50 — The Solution: Prescribing Intervals Based on %VLamax 10:30 — Training Zones Builder Demo: VLamax as the Master Metric
🏔️ 4-Day Hands-On Camp with Sebastian Weber: https://inscyd.com/coaching-testing-camp/ 🧪 See INSCYD in action: https://inscyd.com/demo
Subscribe for more exercise science from the coach behind 9 World Championship titles → https://www.youtube.com/@INSCYD?sub_confirmation=1
So, here we are looking at the hit training 40 seconds on at 130% of threshold, 20 seconds off at 50% of threshold. And on the Y axis, you do see the percentage utilization of VLA max. Basically, the demand relative to VLA max that we're putting in during the on phase.
Here we have an athlete with a VLA max of 0.4 millimoles per liter per second. This is a relatively high VLA max athlete. So the demand during the on phase relative to their V-max is around, let's say, 65 to 70%, which is a very high relative demand.
The off phase at 50% threshold is a very low relative demand on the glycolytic system, maybe 5 to 10%. So what we're saying here is that this athlete is spending a lot of time in very high demand of the glycolytic system and very little time recovering the glycolytic system. So the net effect of this training on VLA max is neutral or potentially lowering.
Now contrast that with Norwegian 4x4. Four minutes at 90% VO2 max, four minutes at 50 to 60% threshold. On the Y axis again, the demand relative to VLA max.
During the four minutes at 90% VO2 max, the demand on the glycolytic system is around 30 to 40% of VLA max. That's moderate. Not low, not extreme.
And during the recovery, 4 minutes at 50 to 60% threshold, essentially zero glycolytic demand. So the ratio of glycolytic stress to glycolytic recovery is much more favorable for improving VO2 max without negatively impacting VLA max. And this is the fundamental reason why Norwegian 4x4 tends to increase VO2 max more reliably than HIIT protocols that use very short intervals at very high intensities.
Because the short high-intensity intervals keep pushing the glycolytic system to its limits during each rep, and the short recovery periods don't fully restore it, so the net signal over many sessions is a downward pressure on VLA max. Whereas Norwegian 4x4 provides enough of a stimulus to drive VO2 max adaptations while preserving or even slightly reducing VLA max, which for endurance athletes is often desirable. So the takeaway from this simulation is not that HIIT is bad.
It's that the specific protocol matters enormously. And understanding the glycolytic demand relative to VLA max is what allows coaches to predict whether a training protocol will actually improve the metrics their athlete needs for their specific event.
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