Birmingham, Oct 12 (The Conversation) Imagine if your smartwatch didn’t just tell you how many steps you’ve walked or calories you’ve burned, but how many heartbeats you’ve “spent” each day.

According to a recent study, that number might one day become another marker of health – a “heartbeat budget” that could, in theory, tell you if you’re overspending your most vital resource.

The idea of a lifetime heartbeat limit has floated around for decades. It’s based on an old myth that the heart comes with a fixed number of beats, often said to be about 2.5 billion, so every extra one you use brings you closer to running out. Thankfully, that’s pretty roundly accepted now to be untrue.

Exercise doesn’t shorten your life by making your heart beat faster. If anything, people who exercise tend to

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