Training with heart-rate zones during interval work

Zones are proportions of your maximum heart rate: roughly under 60 percent for zone one, then 60 to 70, 70 to 80, 80 to 90, and 90 and above for zone five. Pair a standard Bluetooth chest strap and the run screen shows which zone you are in as you work.

Interval training does not sit in one zone the way steady cardio does. Heart rate climbs during a station, falls during rest, and climbs again — so an average across the session can land in zone three while you barely spent a minute there. Time in zone is the more useful number: it tells you how the session was actually distributed.

That distribution is what makes rest a programming decision rather than an afterthought. Long rest lets heart rate drop far enough that the next effort starts fresh, which keeps power high but pulls total time in the upper zones down. Short rest keeps heart rate elevated throughout and shifts the session toward conditioning at the cost of output per station.