If you've spent any time in wellness spaces lately - online or in real life - you've almost certainly heard someone talk about Zone 2 cardio. It's become the darling of the longevity crowd, praised for its benefits to metabolic health, endurance, and fat burning. The only problem? Ask five different apps what Zone 2 actually is, and you'll get five different answers.
It's all about heart rate - sort of
The zone system is built around heart rate. The basic idea is that different intensity levels of exercise correspond to different physiological states in your body, and by training in specific zones, you can target specific outcomes. Zone 2, in theory, is a moderate, sustainable effort - often described as the pace where you can hold a conversation but wouldn't exactly call it easy.
The catch, as Lifehacker points out, is that each platform has its own interpretation of where one zone ends and another begins. Your Garmin watch might tell you you're in Zone 2 while your Whoop app or Apple Watch disagrees entirely. Even fitness coaches and researchers don't all use the same definitions.
Why the confusion exists
Part of the issue is that heart rate zones were never standardized across the industry. Different models use different formulas to calculate your maximum heart rate, and the percentage ranges assigned to each zone vary depending on who developed the system. Some use a five-zone model, others use six or even seven. The math simply doesn't land in the same place.
There's also a meaningful difference between heart rate-based zones and zones determined by metabolic markers - like lactate threshold testing, which requires a lab and is far more precise but obviously not accessible to most people. The numbers on your phone are an estimate, and a rough one at that.
So should you even bother?
Honestly? Yes - with some perspective. The underlying principle of Zone 2 training is solid even if the exact numbers are fuzzy. Spending time doing moderate, sustained cardio where you're working but not gasping is genuinely good for you. The research supporting that kind of training for heart health and endurance is real.
The practical takeaway is to treat the zones on your device as a rough guide rather than gospel. Pay attention to how you feel - can you breathe through your nose? Could you sustain this pace for an hour? That lived experience might actually be more useful than chasing a specific number on a screen.
Fitness tech is incredible, but it's still an approximation of something happening inside your body. Use it as a starting point, not a rulebook.
