If you know your maximum heart rate—not estimated, but your actual maximum, the highest number you’ve ever seen on a heart rate monitor—your zone 2 will correspond to between approximately 70 and 85 percent of that peak number, depending on your fitness levels. That’s a big range, so when starting people out, I prefer they rely on their rate of perceived exertion, or RPE, also known as the “talk test.” How hard are you working? How easy is it to speak? If you’re at the top of zone 2, you should be able to talk but not particularly interested in holding a conversation. If you can’t speak in
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