Zone 2 Training: Why More Isn’t Always Better for Age-Group Athletes

William Horkoff
Aug 25
3 min read

In recent years, Zone 2 training has become the hot buzzword in endurance sport. Scroll through YouTube or Instagram and you’ll hear that it’s the “superpower” behind world-class athletes. But is Zone 2 really as magical as it sounds or is the story more nuanced?

Let’s break down what Zone 2 actually is, what the science says, and why pros spend so much time there.

Defining the Training Zones

To understand Zone 2, we need to revisit how training zones are structured. True training “zones” aren’t arbitrary they’re anchored to physiological thresholds:

Zone 2 → Zone 3 benchmark: around the first lactate or ventilatory threshold (LT1 / VT1)
Zone 4 → Zone 5 benchmark: around the second lactate threshold or critical power (LT2 / CP), often approximated by FTP

Zone 2 is typically described as “easy” or sustainable. That’s not just perception at this intensity, your body shows minimal metabolic disruption (low lactate, stable ionic balance, preserved phosphocreatine). Almost all energy comes from aerobic metabolism, making it the foundation for endurance fitness.

Why Pros Spend 80–90% Below Threshold

Multiple studies have shown that elite endurance athletes from Tour de France podium finishers to Olympic skiers and triathletes spend the majority (80–90%) of their training time below LT1.

For example:

Case studies of Giro d’Italia and Tour de France top-5 finishers showed that most training time was kept under ~80–85% of FTP, which aligns with Zone 2.
Norwegian coaches (the same group behind Olympic champions and world-record holders) prescribe similar distributions across sports: high volumes of low-intensity work, with just 10–20% at moderate-to-high intensity.

The logic? Low-intensity training allows massive volume accumulation without overloading the body, creating the aerobic “base” needed for top-level performance.

But Here’s the Question: Is Zone 2 Intrinsically Better?

The hype around Zone 2 often suggests it’s the best stimulus for aerobic development. But what happens when we compare Zone 2 with higher-intensity training if we match the total energy expenditure?

That’s exactly what a 2024 study from the University of Calgary set out to test.

The Study: Zone 2 vs Higher Intensities

Inglis and colleagues (2024) recruited 84 recreationally active men and women (~26 years old, VO₂max ~42 ml/kg/min) and split them into 6 training groups over 6 weeks:

Zone 2: 3 × 50 min at ~65% FTP (below LT1)
Zone 3: 3 × 41 min at ~80% FTP (just above LT1)
Zone 4: 3 × 30 min at FTP (critical power)
Zone 5: 5–6 × 4 min intervals at ≥120% FTP
Zone 6: 3–6 × 30 sec all-out sprints with long recovery
Control: no training

Importantly: total work was matched across groups (except Zone 6 and control), meaning the calorie/energy expenditure was the same.

What They Found

VO₂max Improvements

Zone 2: +1.8 ml/min/kg
Zone 3: +3.3
Zone 4: +5.4
Zone 5: +6.2
Zone 6: +4.7
Control: no change

First Threshold (LT1) Gains

Zone 2: +16 W
Zone 3: +25 W
Zone 4: +26 W
Zone 5: +24 W
Zone 6: +25 W

Second Threshold (LT2/CP) Gains

Zone 2: +11 W
Zone 3: +19 W
Zone 4: +20 W
Zone 5: +28 W
Zone 6: +16 W

Key Takeaways

Higher intensity = greater aerobic adaptations (when work is matched).
VO₂max and threshold improvements increased progressively from Zone 2 → Zone 5. Zone 5 (hard intervals) delivered the most robust gains.
Zone 2 isn’t “magical.”
It’s effective, but not intrinsically superior to other zones for building VO₂max or thresholds.
Why pros still do so much Zone 2:
The secret isn’t that Zone 2 is better per calorie spent. It’s that you can do a lot more of it. High-intensity work comes with greater fatigue, recovery demands, and injury risk. Zone 2 allows huge training volumes without breaking the system.
For time-crunched athletes:
Copying the 80–90% distribution of pros doesn’t make sense. You’ll likely see better returns by focusing on 2–3 key interval sessions per week (Zones 3–5), with additional low-intensity work if your schedule allows. As always, appreciate anyone who takes the time to read these blogs! Shoot me a message via the contact form, instagram DM, etc. If there is anything you would like me to dive into next.