The Science of Sport • Training
Easy, Lactic, VO2: The Simple 3-Zone Guide to Training Smarter
Five training zones sound scientific. Three are far easier to use. Here's how the zones work, why they need each other, and how much time CrossFit, HYROX, marathon and Ironman athletes typically spend in each.
Why zones exist
Training is a dose. The same session can be a gentle top-up or a big hit depending on how hard you do it, and different intensities train different parts of your body. Zones are simply a way of labelling intensity so you can put the right dose in the right place, instead of going medium-hard on everything.
The classic 5 zones
Most watches and coaches use five zones, based on a percentage of maximum heart rate (or threshold). Exact numbers vary by system and athlete, so treat these as a guide.
| Zone | Roughly | Feels like |
|---|---|---|
| Zone 1 Recovery | 50 to 60% max HR | Very gentle. You could chat all day. |
| Zone 2 Aerobic base | 60 to 70% max HR | Easy and conversational. Breathing through the nose is possible. |
| Zone 3 Tempo | 70 to 80% max HR | Comfortably hard. Short sentences only. |
| Zone 4 Threshold | 80 to 90% max HR | Hard. A few words at a time. Burning builds. |
| Zone 5 VO2 max and above | 90 to 100% max HR | Very hard. Only sustainable for minutes. |
Why we prefer 3 zones
Five zones are useful for data, but they create two problems. First, the lines between them are blurry: heart rate lags, drifts with heat and fatigue, and the boundaries differ between athletes and between systems. Second, zones 3 and 4 tempt people into the grey area, where sessions feel productive but are neither easy enough to recover from nor hard enough to drive big change.
A 3-zone model fixes that by tying zones to what actually changes in your body. There are two clear thresholds: the point where breathing and effort start to step up, and the point where effort stops being sustainable for long. Between them you get three simple buckets.
Zone 1: Easy (the engine)
Covers: old zones 1 and 2. Feels like: conversational, relaxed, finishing feeling like you could do more.
What it builds: aerobic base. More capillaries, more mitochondria, better fat use and a stronger heart. It's also where most recovery happens, because it is hard enough to help but gentle enough not to cost you tomorrow's session.
Zone 2: Lactic (the ceiling you can hold)
Covers: old zones 3 and 4, around threshold. Feels like: hard but controlled. You can hold it for roughly 20 to 60 minutes, and you're counting down the time.
What it builds: the ability to clear and tolerate lactate while sustaining a high pace. Raising this threshold lifts the pace you can hold in a race, whether that's a 10 km, a HYROX or the run leg of a triathlon.
Zone 3: VO2 (the top end)
Covers: old zone 5 and above. Feels like: very hard, in intervals of roughly 2 to 5 minutes with proper rest.
What it builds: your maximum oxygen uptake, the size of the engine. It also trains power, running economy and the ability to tolerate discomfort.
Simple rule of thumb: easy should feel easy, lactic should feel controlled and hard, VO2 should feel very hard and short. If a session lands in the murky middle, it usually pays to push it clearly to one side or the other.
How the zones support each other
Think of a house. Easy work is the foundation, lactic work is the structure and VO2 work is the roof height. You can't build a tall roof on a weak foundation.
- Easy supports lactic. A bigger aerobic base means more of your work at threshold is powered aerobically, so you clear lactate more efficiently and hold the pace longer.
- Easy supports VO2. A strong base helps you recover between hard intervals, so you can repeat them with quality, and recover from the sessions themselves.
- VO2 supports lactic. Raising your top end lifts the ceiling. If your maximum goes up, the pace at your threshold usually goes up with it.
- Lactic supports everything on race day. It's the pace you can actually sustain, so it connects fitness to performance.
- Easy protects the hard. Keeping most sessions truly easy leaves you fresh enough to do the hard sessions properly. Hard days hard and easy days easy is the pattern behind most good training plans.
Why train all three
Each zone fixes a different limit. Train only easy and you build a big engine with no top gear. Train only hard and you burn out, plateau or get injured, because the foundation isn't there to absorb it. Training all three covers the full range: capacity, sustainability and speed. It also keeps training varied and gives your body different signals to adapt to.
How much time in each zone?
The most-quoted standard is the 80/20 or polarised approach: roughly 75 to 80% of training time easy and 20 to 25% hard (lactic plus VO2 combined). Research on elite endurance athletes keeps finding this kind of pattern. How the hard share is split depends on the sport and the phase of training.
The numbers below are typical starting points based on common coaching practice, not rules. Adjust for your experience, how close your event is, and how you're recovering.
| Sport | Easy | Lactic | VO2 |
|---|---|---|---|
| CrossFit | 50 to 60% | 15 to 25% | 20 to 30% |
| HYROX | 60 to 70% | 20 to 30% | 10 to 15% |
| Marathon | 75 to 80% | 15 to 20% | 5% |
| Ironman | 80 to 85% | 10 to 15% | 3 to 5% |
Approximate share of weekly endurance training time. Strength work and skill sessions are in addition.
CrossFit
CrossFit is high on intensity by nature, so the risk is doing everything too hard. Add easy aerobic work (bike, run, row) to build the base and improve recovery between rounds. Keep a couple of lactic and VO2 days for the metcon-style work the sport demands.
Example week (about 6 hours of conditioning): 2 easy 45 to 60 minute sessions; 1 lactic session such as 3 x 10 minutes at threshold on a bike or rower; 1 VO2 session such as 5 x 3 minutes hard with equal rest.
HYROX
A HYROX race is about an hour of running broken up by eight stations. It lives near threshold, so the lactic zone is the star, and you need a strong base so the running holds up across 8 km. A little VO2 sharpens the top end.
Example week (about 7 hours): 3 easy runs or bike sessions; 1 lactic run such as 4 x 8 minutes at threshold; 1 compromised session of run, sled and wall balls at threshold effort; 1 short VO2 session such as 6 x 2 minutes hard; plus strength work.
Marathon running
Marathon pace sits at the top of the easy zone and the lower end of lactic, so most of the work is easy volume with a weekly session around threshold or marathon pace. Short VO2 efforts keep speed and economy topped up.
Example week (about 5 to 6 hours): 3 to 4 easy runs, one of them long; 1 lactic session such as 3 x 10 minutes at threshold; 1 short VO2 session such as 5 x 3 minutes hard (an optional extra).
Ironman triathlon
Ironman is the most base-heavy of the four. Race day is a long, controlled effort across 8 to 17 hours, and the volume across three sports means recovery is the limiter. Nearly everything is easy, with a small amount of threshold and a pinch of VO2.
Example week (about 12 to 15 hours): swim, bike and run mostly easy, including a long ride and a long run; 1 to 2 lactic sessions such as 3 x 15 minutes at tempo on the bike; 1 short VO2 session in the build phase only.
Common mistakes
- Easy days that aren't easy. If you can't chat, slow down.
- Living in the grey zone. Medium-hard everything feels productive but is hard to recover from.
- Too much hard, too soon. Build the base first, then sharpen.
- Ignoring recovery. Sleep, food and fuelling decide how well you absorb the work.
Fuel and recover to match the zone
- Hard days: Athletic Energy before, and Sonic Energy for carbohydrate and electrolytes on longer sessions.
- After training: Phyto-Fusion plant protein to support recovery.
- Every day: Gut Guardian to support the gut, which gets stressed when intensity and volume go up.
The takeaway
You don't need five zones to train well. You need three: easy to build the engine, lactic to raise the pace you can hold, and VO2 to lift the ceiling. Spend most of your time easy, a deliberate slice at threshold, and a small dose at the top end. Keep the hard days hard, the easy days easy, and let each zone do its job.
This article is for educational and informational purposes only and is general in nature. Training percentages and examples are typical starting points, not individual advice. Speak with your doctor or a qualified coach before starting or changing a training program, especially if you have a medical condition. These statements have not been evaluated by the TGA. Supplements are foods / complementary medicines and are not intended to diagnose, treat, cure or prevent any disease. Always read the label.
