Running in winter: cold, dark, ice and the 5 °C rule
Winter is the season of spring preparations: Paris, London, Seville, Barcelona are won in January. Cold, darkness and ice change the sessions. Here is the 5 °C rule your AI coach applies, what it moves and what it keeps, and how it reads your winter runs on Garmin.
Last updated: 2026-09-19
The 5 °C rule
Below 5 °C, the warm-up goes from 15 to 20 minutes, with strides placed at the end of the warm-up, never at the start. Cold muscles get hurt on short intervals: below 0 °C or on frozen roads, the short VMA session is replaced by threshold or medium hills.
Pace targets stay the same: moderate cold does not slow you down, it cools you. Heat changes paces, winter does not.
Darkness and ice
Quality sessions are preferably run at the weekend in daylight, or on a lit, familiar route during the week. The plan places them according to the days you indicate; tell it you run at night and it will avoid long intervals on weekdays.
Ice: the long run is moved by 48 hours rather than run on frost. The coach accepts it without penalty, it is the only session it has you make up.
Reading winter runs
Heart rate is slightly lower at equal pace in cold weather: it is not a sign of fitness, it is thermoregulation. The coach compares sessions in comparable conditions and points it out in the review.
- Below 5 °C: 20-minute warm-up, strides at the end.
- Below 0 °C or frost: no short VMA, threshold or hills.
- Ice: long run shifted 48 h, never run on frost.
The watch sometimes loses the optical heart-rate signal in deep cold, fingers and wrist being less perfused. A chest strap fixes it for sessions with an HR target.
Frequently asked questions
Should you run slower in winter?
No, except in icy wind or on frozen ground. Moderate cold does not slow you; heat is what requires reducing paces.
Does the treadmill replace winter runs?
For quality sessions, yes, at 1% incline. The long run stays outdoors as much as possible: it is mental training too.
How should I dress?
As if it were 10 °C warmer than forecast, with a layer you can remove. Test the race kit on a long run before a winter race.
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