Alternate one kilometre hard with one kilometre steady aerobic float. The structure is the useful part: effort can change with terrain, weather and the point of the training week without changing the identity of the session.
Exact workout
[1 km Zone 5 effort → 1 km steady aerobic Zone 2 float] × 4
The on kilometre is Zone 5 by feel. The float is steady aerobic Zone 2 rather than easy recovery. Zones are guidance only. Garmin steps remain open.
Use the zones as broad effort guidance, not enforced watch targets.
Longer option: Repeat five times for 10 km.
Build it in Garmin Connect
Create a 1 km Run step named On and a 1 km Run step named Float. Repeat the pair four times for 8 km. Leave both targets open.
Start it on the watch
Sync the workout to the watch. Open the Run activity, then Training or Workouts, select the workout and choose Do Workout. Menu wording varies by model.
Optional warm-up: 2 km at conversational effort. Optional cool-down: 1–1.5 km at conversational effort. Adjust or stop when pain changes movement, conditions become unsafe or the planned effort is clearly wrong for the day. Completing the saved file is never more important than preserving the purpose of the week.