What is easy pace running?
Easy pace is the speed at which you can hold a full conversation — not fragments of sentences, but complete, unhurried sentences. If you're gasping between words, you're running too fast. This is the operational definition, and it's more useful than any heart rate zone because it doesn't require a device.
For most half marathon runners, easy pace is meaningfully slower than you might expect: 6:30–8:00 min/km depending on fitness. Runners targeting sub-2 hours often have an easy pace of 6:30–7:00 min/km. Runners targeting 2:30 are closer to 7:30–8:00 min/km.
The reason this surprises people is that easy running feels almost embarrassingly slow. You feel like you're not working hard enough for it to count. That feeling is wrong. At easy pace, you are training the aerobic system responsible for 80% of your race day energy output — and you're doing it without accumulating the fatigue that makes your next hard session worse.
What does zone 2 training actually do?
Zone 2 (roughly 60–70% of maximum heart rate, or easy conversational pace) primarily stimulates mitochondrial biogenesis — the creation of new mitochondria in your muscle cells. Mitochondria are the cellular machinery that convert fat and oxygen into energy. More mitochondria means more aerobic capacity.
It also improves fat oxidation — your body's ability to use fat as fuel rather than relying entirely on glycogen (stored carbohydrate). Runners with better fat oxidation can maintain race pace longer before depleting their glycogen stores, which delays the fading that happens in the final 5 km of a half marathon.
These adaptations happen at easy pace specifically. Running harder than zone 2 does not stimulate them more — it primarily stimulates different, anaerobic adaptations. Running your easy runs too hard doesn't make you fitter in the right way; it just makes you more tired.
The 80/20 principle: what it means in practice
Sports scientist Stephen Seiler's research on elite endurance athletes found that they consistently spend about 80% of training time at easy intensity and 20% at hard intensity — with very little in between. This distribution produces better results than polarising differently or spending most time at moderate intensity.
Most amateur runners accidentally train at moderate intensity for most of their runs — too fast to be genuinely easy, too slow to be genuinely hard. This grey zone produces some fitness improvement but is suboptimal for both aerobic base development and anaerobic threshold improvement.
Applying 80/20 to a four-day training week looks like this: three runs are genuinely easy (conversational pace), one run is genuinely hard (tempo or intervals at significant discomfort). The hard run is possible and productive because the easy runs didn't accumulate fatigue.
- →80% of weekly mileage at easy/conversational pace
- →20% at quality pace (tempo, intervals, or race pace)
- →Nothing in the 'medium' zone — medium is neither recovering nor adapting
- →The hard sessions are hard because the easy sessions are genuinely easy
How to find your easy pace
The talk test: if you can't speak a complete, unhurried sentence, slow down. This is the simplest and most reliable method. It doesn't require a heart rate monitor and it adjusts automatically for weather, terrain, and daily fatigue.
Heart rate method: for most runners, easy pace corresponds to 60–70% of maximum heart rate. Your maximum heart rate is roughly 220 minus your age (a rough estimate — individual variation is significant). For a 35-year-old, maximum heart rate is approximately 185 bpm, making zone 2 roughly 111–130 bpm.
Pace calculator method: if you know your recent race time, you can calculate easy pace. For a runner with a 2:00 half marathon time, easy pace is typically around 6:30–7:00 min/km. For a 1:45 runner, around 5:50–6:20 min/km. These ranges exist because easy pace depends on daily conditions, not just fitness.
What happens if you run easy runs too fast?
You arrive at your quality sessions — tempo runs, interval sessions — already carrying fatigue. The session feels harder than it should for the pace you're running, so you either slow down (reducing the training stimulus) or push through (accumulating more fatigue). Neither outcome is good.
Over several weeks, this pattern creates a training plateau. Your easy runs feel like moderate effort rather than recovery. Your hard sessions feel unsustainably hard. Your race times stop improving even as your training volume increases. This is the grey zone — and easy pace discipline is the exit.
The counterintuitive fix: slow your easy runs down significantly for 4–6 weeks. Your hard sessions will start feeling genuinely productive rather than survival mode. Within 6–8 weeks, your race paces will improve not because you trained harder, but because you recovered better between the sessions that actually mattered.