The heart rate zone formula is flawed, especially for women. Here's how to rethink your training.

That tension becomes especially clear with heart rate zone training, a popular five-tier system that endurance athletes use ...

Why zone 3 cardio is just as good as zone 2

Zone 2 is good for long sustained efforts. It's usually OK to do zone 2 in place of a rest day. Zone 3 helps you adapt to ...