In the most recent hiking training video from Outdoor Adventure Training, Mikey Bell broke down all five heart rate training zones. Zone 2 training, which dominates fitness podcasts and wearable marketing, builds an aerobic base but does nothing to raise your cardiovascular ceiling. Zones 3, 4, and 5 are required for that, but calculating the zones themselves can be quite a problem on its own.
Most smartwatches calculate maximum heart rate using the formula 220 minus your age, an equation dating back to the 1970s with a standard error of plus or minus 12 beats per minute. Research from Norway’s HUNT Fitness Study, which tested more than 3,000 adults, found the formula can miss a person’s actual maximum by up to 40 beats per minute in older demographics, an error that cascades across every training zone.
Bell recommends the HUNT formula instead: 211 minus 0.64 multiplied by your age. A 55-year-old gets a maximum heart rate of 176 rather than 165, pushing every zone boundary meaningfully higher.
Wrist-based heart rate monitors can push the problem even further, with research showing they can be off by 10 to 15 percent and accuracy dropping as intensity rises. Chest monitors, which read electrical heart activity directly, are accurate to within one to two beats.
