Norwegian 4x4 for crossfit
Written by Conquer Athlete Head Coach, Jason Leydon, CSCS
In mixed-modal sports like CrossFit, everyone talks about strength and skills, but the real limiter for most athletes is their engine. When the loads are reasonable and the skills are well within your comfort zone, the athletes who win are usually the ones who can hold a higher pace for longer and repeat that effort with less drop-off. That capacity isn’t random, it’s a function of your energy systems, your VO₂max, and where your thresholds sit relative to that VO₂max. The Norwegian 4x4 method is one of the most effective, structured ways to push those qualities upward.
Energy systems 101 for mixed modal work
Every WOD pulls from all three energy systems, but the emphasis changes with the task:
ATP–PCr (phosphagen):
Fuels maximal efforts up to ~10 seconds, heavy singles, short sprints, explosive efforts.Anaerobic glycolytic (glycolytic):
Dominant from about 20 seconds to 2 minutes of hard work, think sprint intervals, nasty openers in classic CrossFit pieces. High power, but high by-product accumulation.Aerobic (oxidative):
Dominant as duration extends beyond ~2 minutes, and crucial for recovery between repeated bouts of higher-intensity work. It keeps you moving and clears fatigue between efforts.
In a typical mixed-modal session, you’re constantly sliding along this continuum. The athlete with a robust aerobic system doesn’t just pace better in a 20-minute AMRAP, they also recover faster between heavy sets, between metcons in a training day, and even between days of competition. That’s why building the “engine” is not optional; it’s the platform everything else sits on.
VO₂max and thresholds: why they separate athletes
VO₂max is the maximum rate at which you can take in and use oxygen during intense exercise. It sets the upper ceiling for aerobic power. You can’t sustain work for long above 100% of your VO₂max, so a higher VO₂max gives you a higher ceiling for sustainable work.
But VO₂max alone doesn’t explain performance. Two other key pieces matter:
Aerobic (first) threshold (LT1 / VT1):
The intensity where lactate and ventilation start to rise above resting but are still manageable. Below this, you can go for a long time with minimal fatigue.Anaerobic (second) threshold (LT2 / VT2):
The intensity just below the point where lactate accumulation and ventilation spike sharply. This is often called “lactate threshold” or “functional threshold” in endurance circles.
In trained endurance athletes, the second threshold typically sits around 75–90% of VO₂max. The closer that threshold is to your VO₂max (i.e., the higher your fractional utilization), the harder you can work aerobically before you’re forced to “pay” heavily with glycolytic contribution and fatigue.
For competitive CrossFit athletes, research shows that those at the top level tend to have higher VO₂max and better aerobic capacity than recreational athletes and active adults. Studies looking at physiological predictors of CrossFit performance consistently find that aerobic markers (VO₂max and thresholds) are important contributors alongside strength and power.
So when strength and skills are roughly equal, the separator is often:
How high your VO₂max is (your ceiling), and
How high your thresholds are relative to that ceiling.
For CrossFit, a practical target is to push your anaerobic threshold toward 85–90% of VO₂max, and your aerobic base strong enough that a lot of your “easy” training sits well below that threshold without excessive fatigue. That’s where methods like the Norwegian 4x4 come in.
What is the Norwegian 4x4 method?
The Norwegian 4x4 is a high-intensity interval protocol developed and validated by physiologists in Norway, particularly at the Norwegian University of Science and Technology. The classic format is:
Warm up for 8–10 minutes.
4 × 4 minutes at ~90–95% of HRmax (or an RPE ~8–9/10).
3 minutes of active recovery between intervals at an easy pace (~60–70% HRmax).
Cool down for a few minutes.
What makes it powerful is the time spent near VO₂max. Helgerud et al. showed that 4×4-minute intervals at this intensity produced significantly larger increases in VO₂max than long slow distance or classic threshold training, with improvements of ~7–13% in just a few weeks in trained individuals.
Mechanistically, these intervals:
Stress the heart enough to drive increases in stroke volume and cardiac output.
Provide a large oxygen demand to stimulate mitochondrial adaptations in working muscle.
Accumulate a lot of high-quality work around VO₂max, rather than a few short brutal sprints or long slow miles.
To perform it well:
The hard intervals are not all-out sprints; they’re a hard, steady effort you could maybe sustain for 8–10 minutes if you had to.
The recoveries are genuinely easy but not complete rest—you keep moving.
You control the pace or power so that your heart rate climbs into the target zone and stays there for most of each 4-minute block.
Done 1–2 times per week, this becomes a very efficient way to raise VO₂max and the intensity you can sustain before hitting your anaerobic ceiling.
Why the Norwegian 4x4 matters for CrossFit—and how to use it
For CrossFit, the method is valuable, but how you apply it matters even more than the protocol itself.
1. Exercise selection to drive systemic, not local, fatigue
If you use the 4×4 format with mixed-modal pieces, you must select movements that let you stay in the desired heart rate and breathing zones without failing locally.
Good options for “engine-focused” 4-minute blocks:
Monostructural: row, bike, ski, running.
Simple mixed pieces: light thrusters, burpees, box jump-overs, KB swings.
Movements that are too heavy, too grip-dominant, or too skillful (e.g., max-weight snatches, high-volume HSPU, complex gymnastics) will cause local muscular failure or technical breakdown before you create the central aerobic stress you’re after.
2. Rep scheme and structure; continuous work at the right intensity
Within each 4-minute block, structure the work so the athlete can keep moving at a steady, hard pace:
Example: 4 minutes of
8 cal row
6 barbell thrusters
4 burpees
The goal is to move continuously at a repeatable effort that lands around 90–95% HRmax or an RPE of 8–9, not to sprint the first round and hang on.
If you’re using pure machines, that might look like 4 minutes at a prescribed wattage/pace that corresponds to that intensity.
3. Respect individual differences
Two athletes will hit 90% HRmax at very different wattages, paces, and loads. To get the intended adaptation:
Adjust load (lighter or heavier barbell weights).
Adjust movement choice (bike instead of run for someone with beat-up knees).
Adjust target pace or reps per minute based on the athlete’s current VO₂max and thresholds.
Masters athletes and newer members may need to start with 2–3 intervals or slightly lower intensity (e.g., high Zone 3 / low Zone 4) and progress over time.
4. Integrate with the rest of the week
Norwegian 4x4 work is demanding. In a CrossFit training week, you’d typically:
Place it on a day that is not already loaded with high-CNS strength work.
Limit it to 1–2 sessions per week, paired with lower-skill accessory or tempo work.
Maintain other engine pieces (longer easy aerobic work, threshold sessions) so the 4x4 sits in a broader progression, not as a random “smash yourself” day.
The takeaway
An efficient engine for CrossFit means:
A high VO₂max (big ceiling),
Thresholds that sit at a high percentage of that VO₂max, and
The ability to express that capacity in mixed-modal settings without breaking down.
The Norwegian 4x4 method is a simple, research-backed way to spend large amounts of quality time near VO₂max and push those ceilings and thresholds upward. When you apply it with intelligent exercise selection, appropriate rep schemes, and individual scaling, it becomes a powerful tool, not just for runners and cyclists, but for CrossFit athletes who want to separate themselves when everyone else already lifts heavy and moves well.
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