Easy
What it trains: your aerobic engine: more capillaries, more mitochondria, better fat burning, stronger tendons. It is the bulk of marathon training and the pace of every long run.
How fast: 15 to 27% slower than marathon pace. For a 4-hour marathoner that is about 6:30 to 7:15 per km. You should be able to hold a conversation.
The trap: running easy days too fast. It feels productive, but it leaves you tired for the sessions that matter and adds little fitness.
Marathon pace
What it trains: the exact rhythm of race day: running economy at that speed, fuelling on the move, and the feel of a pace you must hold for hours.
How fast: your goal time divided by 42.195 km. In Run 42 plans it appears in the peak phase, as runs of 8 to 12 km and as 2×5 km blocks at the end of long runs.
Threshold
What it trains: the speed you can sustain before fatigue builds up quickly. Raising it makes marathon pace feel easier.
How fast: the pace you could race for about an hour: “comfortably hard”, where you can say a short sentence but not a paragraph. Typical sessions: 3×8 min, 3×10 min, then 2×15 min with short jogs between.
VMA
What it trains: VMA (vitesse maximale aérobie, maximal aerobic speed) is the speed at which you reach your maximum oxygen uptake. Short repeats near it improve your top-end aerobic capacity and running form.
How fast: about your 3 km race pace. Typical sessions: 6×400 m, 8×400 m, then 5×800 m, with a minute or so of jogging between. Fast but composed: form first, speed second.
Why zones come from race equivalents
Many plans set zones as a fixed offset from marathon pace, say “threshold is 20 seconds faster”. That is too aggressive for slower runners and too soft for faster ones. Run 42 works each zone out as an equivalent race performance using Riegel’s formula, so the gaps scale with you: a 3-hour marathoner’s threshold sits about 15 s/km faster than marathon pace, a 5-hour marathoner’s about 35 s/km. Both bands lean slightly to the slow side, because running hard sessions too fast is the usual mistake.
Find your numbers in the marathon pace chart or from a recent race with the race time predictor.
