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Cardio zones aren’t real—not in the way your fitness app makes them sound, anyway. Yes, heart rate zones are a way to describe how hard you’re working during a cardio workout, like running or cycling. But the cardio zones everyone’s always buzzing about are just a way of bucketing exercise intensity into digestible categories. They’re a useful shorthand, but there are no physiological lines in the sand where your body suddenly switches from “zone 2” to “zone 3.” It’s a spectrum, and the specific cutoffs vary depending on who you ask (or what app you’re using), what formula they rely on, and whether they measured your lactate threshold in a lab or just guessed based on your age.
So when “zone zero” started circulating in wellness circles, my instinct was to roll my eyes. Relying on the zone framework in this way
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