I was doing some research on training recently, and I came across a couple of new papers that I wanted to share with you. There’s been a lot of buzz about zone 2 — and plenty of myths floating around — so let’s clear a few things up. My goal here is to give you the facts, explain where the science is shifting, and show you how I use zone 2 in coaching so you can apply it to your own training.

Two recent papers — one published in Sports Medicine, June 2025 and another in Applied Physiology, Nutrition, and Metabolism, 2022 — reached very different conclusions, even though they shared an author! It’s no wonder athletes and everyday exercisers alike are confused.

---

What is Zone 2 (Aerobic Capacity)?

Zone 2 — sometimes called aerobic capacity training — is a steady effort just below your first lactate threshold. It feels “comfortably hard” — you can sustain it for a long time, but it’s not a relaxed recovery pace either.

In practice:

• Cycling: a steady wattage you could hold for hours while fuelling regularly.
• Running: a pace where breathing is controlled but purposeful — steady and durable.
• Swimming: long repeats (e.g. 200s or 400s) at a pace you could keep going for the session, maintaining good technique under controlled effort.
• Metrics: typically around 65–75% of max heart rate or FTP/power — but it’s highly individual.

The main point: zone 2 develops your endurance engine. It trains your body to burn fat efficiently, boosts mitochondrial density, and lays the foundation that makes higher-intensity training sustainable.

---

What’s Changed in the Research?

This is where it gets interesting.

• The 2025 paper argued that for the general population training only a few hours per week, zone 2 may not deliver as much as high-intensity training. It even suggested that high intensity could stimulate both of the main mitochondrial pathways, while zone 2 might not do much at all.
• The 2022 paper, however, took a more balanced stance — saying there’s not enough evidence on zone 2 to draw hard conclusions, and warning against over-selling high intensity.

So, do we ditch endurance work and just do intervals? Not so fast.

The truth, as always, is more nuanced.

---

The Nuance

Definitions and durations matter.

• In some of the research, what was labelled as “zone 2” was set so low it was more like recovery than purposeful endurance work.
• Many studies only lasted 30–90 minutes — too short to create the adaptations endurance athletes are chasing.

And here’s the key: a lack of evidence isn’t the same as proof that zone 2 doesn’t work.

---

Coach’s Corner

Many of my athletes come to me with very different needs. Some only have 3–4 hours a week and want to improve their general health. Others are building towards big goals like a triathlon or long cycling event. The balance looks different in each case — but the one constant is this: without an endurance base, the hard stuff just doesn’t stick.

If you’re short on time, I’ll often include a purposeful zone 2 session and then add a touch of intensity to give you that extra bang for your buck. But if you’re chasing endurance goals, zone 2 becomes the backbone. Those longer, steady efforts — on the bike, in the pool, or on the run — give you the durability to handle harder training later.

Here’s how I structure it across a season:

• Pre-season/Base: Zone 2 is king. Long, steady sessions build resilience, while I also weave in strength work — in the gym and on the bike/run/swim — so you’re building not just endurance, but durability.
• Build phases: Once the base is strong, we start layering everything else on top of endurance — strength, power, and speed. This is where high-intensity intervals sharpen you, but they only work because the endurance platform underneath can support them.
• In-season: The mix depends on your goal. For long triathlons or fondos, endurance still dominates, supported by strength and just enough intensity to race well. For criteriums or short-course triathlon, speed and power take a bigger role, but always laid on top of a strong aerobic engine.

The big lesson: zone 2 isn’t optional — it’s the enabler. It creates the platform that makes strength, power, and speed effective and sustainable. Without it, you’re stacking performance layers on shaky ground.

---

Let’s Make It Personal

Feeling lost in the zone 2 vs HIIT debate? Need clarity for your season?
👉 Book a free Peak Performance Strategy Session with me. Together, we’ll map out your goals and create a clear path forward so you know exactly how to train with purpose.

---

References

1. Storoschuk, K. L., Moran-MacDonald, A., Gibala, M. J., & Gurd, B. J. (2025). Much Ado About Zone 2: A Narrative Review Assessing the Efficacy of Zone 2 Training for Improving Mitochondrial Capacity and Cardiorespiratory Fitness in the General Population. Sports Medicine. SpringerLink
2. Granata, C., Jamnick, N. A., Bishop, D. J., & Gurd, B. J. (2022). Impacts of altered exercise volume, intensity, and duration on the activation of AMPK and CaMKII and increases in PGC-1α mRNA. Applied Physiology, Nutrition, and Metabolism, 47(9), 987–998. ScienceDirect