Power meters changed cycling training. But somewhere along the way, a lot of riders decided that heart rate was outdated and stopped paying attention to it. That is a mistake.
Power tells you what your legs are doing. Heart rate tells you what your body is paying for it. You need both numbers to understand what is actually happening inside your physiology.
The most useful thing you can track with dual metrics is aerobic decoupling. Go out and ride at a steady power — say eighty percent of FTP — for ninety minutes. Compare your average heart rate in the first half to the second half. If heart rate climbed by more than five percent while power stayed flat, your aerobic system is not yet efficient at that intensity. Repeat the test a month later after consistent base work and you should see that drift shrink. That is fitness improvement that the power number alone would never show you.
The reverse is equally valuable. If you hop on the bike for an easy spin and your heart rate is ten beats higher than usual at the same low power, your body is waving a flag. You are under-recovered, dehydrated, fighting off something, or carrying stress. A power-only rider would see normal watts and push on. A dual-metric rider would recognise the signal and adjust.
Heart rate does have limits. It responds slowly, which makes it poor for judging short VO2max intervals or sprints. For anything under two minutes, trust power. But for steady-state rides, tempo efforts, and long endurance days, heart rate adds a layer of insight that power alone cannot provide.
Track both. Compare them regularly. The gap between the two metrics — and how that gap changes over time — is where the real information lives.
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