| Factor | Slow/Easy Running | Interval Training |
|---|---|---|
| Intensity | Zone 1-2 (conversational) | Zone 4-5 (hard effort) |
| VO2 max improvement | Slow and steady | Fast |
| Aerobic base | Primary builder | Maintains, doesn't build |
| Recovery needed | Minimal (24h) | 48-72h |
| Injury risk | Low | Higher |
| Calorie burn/hour | Lower | Higher (with EPOC) |
| Weekly volume | 80% of runs | 20% of runs (elite model) |
Choose Slow/Easy Running when…
You're building your aerobic base, recovering between hard sessions, targeting long distances like a marathon, or following an 80/20 training approach (most of your weekly mileage).
Choose Interval Training when…
You want to improve VO2 max and running speed, are preparing for shorter race distances, have an established aerobic base and want to add speed, or have limited time and need efficient training.
Gear for both
GPS Running Watch
Track pace and heart rate zones for both easy and interval sessions.
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FAQ
Should I always run slowly?
No — a mix of easy and hard is optimal. Elite runners do roughly 80% of their mileage at easy/conversational pace and 20% at threshold or faster. All-easy running stagnates; all-hard leads to injury and burnout.
What pace is 'easy' running?
Easy pace is conversational — you should be able to speak in full sentences without gasping. It feels almost too slow. On heart rate, this is roughly 65-75% of max HR (Zone 2). Many runners run their easy days too fast.
What is 'junk miles' in running?
Junk miles is a contested term describing easy running at a pace that is too fast to provide genuine recovery benefits but not hard enough to generate significant fitness adaptations — essentially time in the 'grey zone' of moderate effort. Whether junk miles exist is debated: some coaches argue all running provides some benefit; others argue that an undifferentiated mix of paces leads to chronic fatigue without clear aerobic development. The polarised training model specifically targets this by discouraging moderate-intensity running in favour of clearly easy or clearly hard sessions.