Zone 2 Training for Hyrox: How Many Hours a Week and Why (Training Science, Part 2)
Zone 2 is the unglamorous foundation of Hyrox performance. Here is what it does at the cellular level, how much you need, what pace and heart rate it corresponds to, and why most Hyrox athletes do far too little of it.
What Zone 2 actually is
Zone 2 is the exercise intensity where the body primarily uses fat as fuel, lactate is produced but cleared at the same rate it is generated, and the demand can be sustained for extended periods without accumulated fatigue. In practical terms: the pace where you can hold a full conversation in complete sentences, your breathing is elevated but easy, and the effort feels almost too easy to be doing anything useful.
That last part is why most Hyrox athletes do too little of it. It does not feel like training. It feels like jogging, and Hyrox is not a jogging event.
This is the error.
The full 5-part Training Science Series
New parts drop every 2nd day. Bookmark the Training Science hub to follow along.
- Part 1 — Concurrent Training for Hyrox: How to Run and Lift Without Sabotaging Either
- Part 2 — Zone 2 Training for Hyrox: How Many Hours a Week and Why (you are here)
- Part 3 — How to Peak for a Hyrox Race: The Final 4 Weeks
- Part 4 — VO2max Training for Hyrox: Intervals That Actually Transfer
- Part 5 — Deload Weeks in Hyrox Training: When to Back Off and What to Do
What Zone 2 does at the cellular level
Zone 2 training drives three key adaptations:
1. Mitochondrial biogenesis. Zone 2 is the primary stimulus for growing new mitochondria — the organelles in muscle cells that produce ATP aerobically. More mitochondria means more capacity to generate energy without relying on anaerobic pathways and the associated lactate and fatigue.
2. Increased fat oxidation rate. Training in Zone 2 increases the muscle cell’s capacity to use fat as fuel — sparing glycogen. A well-trained Zone 2 athlete burns more fat at a given intensity than an untrained one, which means glycogen reserves last longer and the “wall” at the end of a Hyrox is delayed.
3. Elevated lactate clearance capacity. Zone 2 is the zone where lactate is produced and cleared in rough equilibrium. Training this balance increases the body’s ability to shuttle and metabolise lactate, raising the threshold at which it begins to accumulate — which is what the “lactate threshold” training concept actually refers to.
The practical result: a well-developed Zone 2 base means the pace at which you can sustain high-intensity work (like the runs in a Hyrox) is faster, and the pace at which your stations begin to feel unmanageable is higher.
How much do you need?
The general recommendation from the polarised training research (Seiler, Laursen, et al.) is that approximately 80% of training volume should be at or below Zone 2, and 20% at high intensity (Zone 4–5). This is the 80/20 rule.
For a Hyrox athlete training 6–8 hours per week, this means:
- 5–6.5 hours per week at Zone 2 or below
- 1–1.5 hours per week at high intensity (intervals, race-pace station circuits)
Minimum effective dose: Approximately 3 hours per week of Zone 2 training (running, rowing, SkiErg, cycling — all count) to see meaningful adaptation over an 8–12 week block.
Ideal dose: 5–7 hours per week for an athlete training seriously for Hyrox performance.
Most recreational Hyrox athletes are getting 1–2 hours per week of Zone 2 (if that), and filling the rest of their training time with moderate-intensity sessions — too hard to be Zone 2, too easy to drive VO2max adaptations. This “moderate intensity trap” is one of the most common training errors.
What Zone 2 feels like and how to stay in it
The talk test
The most practical field test: Zone 2 is the pace where you can speak in full, complete sentences without gasping between words. If you find yourself needing to catch your breath mid-sentence, you are above Zone 2.
Heart rate targets
Heart rate Zone 2 is approximately 60–70% of maximum heart rate. To find this:
Maximum heart rate estimate: 220 minus age (rough, but useful for calibration).
Zone 2 target heart rate for a 35-year-old: Max HR = 185 Zone 2 = 185 × 0.60 to 0.70 = 111–130 bpm
For a 45-year-old: Max HR = 175 Zone 2 = 105–123 bpm
Important caveat: The 220-age formula is highly imprecise. Individual max HR can vary by 20+ bpm from the estimate. If you have done a genuine max heart rate test (either in a race or a specific field test), use that number.
The most common Zone 2 mistake
Athletes set out at what they think is Zone 2 pace and are actually in Zone 3 (70–80% of max HR). Zone 3 is uncomfortable enough to feel like real training but provides inferior adaptation to either Zone 2 or Zone 4+. It also requires more recovery, crowding out the high-intensity work.
Signs you are above Zone 2:
- Heart rate above 75% of max (with accurate max HR)
- Cannot speak in full sentences
- Breathing through the mouth predominantly
- Rate of perceived exertion above 5/10
If this describes your “easy” runs, slow down. The ego cost is real but the adaptation benefit is significant.
Zone 2 across modalities
Running is the most specific Zone 2 modality for Hyrox (since the race involves 8km of running). But any aerobic modality at Zone 2 intensity drives the mitochondrial adaptations. Options:
SkiErg: Excellent Zone 2 option that also builds SkiErg-specific technique. A 30–45 minute moderate SkiErg session at Zone 2 HR develops both aerobic base and station capacity.
Rowing: Similar to SkiErg. Good for developing the aerobic base while also training rowing mechanics. A 40-minute row at Zone 2 is a high-quality training session.
Cycling (indoor or outdoor): Zero impact, excellent for athletes managing knee or ankle issues. Does not transfer to running economy, but builds the aerobic system.
Walking (brisk): Often dismissed, but brisk walking at Zone 2 HR (which many recreational athletes hit at 6–7 km/h) is a legitimate training stimulus. Good for recovery days or when time is limited.
Building Zone 2 into a Hyrox training week
A sample week that achieves adequate Zone 2 volume for a 6-hour training week:
Monday: Zone 2 run, 40 min (HR 120–135 bpm, conversational pace) Tuesday: Heavy strength session (not Zone 2 — this is the high-intensity day) Wednesday: Zone 2 row or SkiErg, 35 min + light mobility Thursday: Interval run — 4 × 1km at race pace (this is the ~20% high-intensity day) Friday: Rest Saturday: Long Zone 2 run, 60–70 min (this is the most important Zone 2 session) Sunday: Rest or 20 min very easy walk
Zone 2 volume: approximately 2.5–3 hours (Mon + Wed + Sat). This is the minimum effective dose. Add more Zone 2 on Wednesday or add a Tuesday evening short Zone 2 session as fitness improves.
Why Zone 2 is specifically important for Hyrox
Hyrox is not a Zone 2 event — you will race at Zone 4–5 for most of it. But the aerobic base built by Zone 2 training determines how high your Zone 4 ceiling is.
Think of it as building the bottom of the pyramid. The higher you want to go (faster race pace), the wider the base needs to be. Athletes who only do high-intensity work have a narrow, brittle fitness. They can perform one hard effort but cannot maintain it over 8 runs and 8 stations. Athletes with a large Zone 2 base recover between efforts faster, maintain pace later in the race, and burn glycogen more slowly — extending performance through the back half.
What’s next
Part 3 covers the most specific preparation phase: the final 4 weeks before your Hyrox race, and how to taper without losing fitness.
→ Part 3: How to Peak for a Hyrox Race
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