This is the most important thing to track when you run, according to an expert running coach

Woman looks at her watch. She is outside with trees overhead.

Forget pace, cadence, training load and, to a degree, even distance. If there’s one thing you should track above all other metrics when you run, it’s heart rate.

“Heart rate is one of the most important metrics for most runners, and certainly for an all-round audience,” says certified running coach James Stirling—aka London Fitness Guy.