The Idle

Every engine has an idle – that’s the speed an engine runs at when it’s standing still, doing no additional work. Yours is your resting heart rate, the number your watch hands you each morning, and it has more to say than you might think.

Resting heart rate (RHR) is a tug-of-war between your nervous system's gas pedal and its brake. Adaptation to training pulls this number down over months. Almost everything else nudges it up overnight: a hard workout, a short night of sleep, heat, stress, a cold that hasn't announced itself yet.

Two large wearable studies recently put numbers on this. One followed nearly 15,000 people and found that hard efforts ending within four hours of bedtime were linked to a higher overnight heart rate. Sessions that wrapped up earlier showed no effect. Another, covering about 21,000 people, found that having one drink more than your usual (versus one fewer) was tied to an overnight heart rate roughly 2.5 beats higher. Drinking earlier (and less) and sleeping longer softened the hit.

Illness shows up, too. During COVID, wearable data often showed resting heart rate climbing days before people felt sick.

A few ways to use your number:

• Compare you to you. Your baseline over weeks matters, not your riding buddy's number.

• One morning of high RHR is weather. Three in a row is a forecast.

• When RHR is up and your legs feel like junk, make it a recovery day.

Before you go full-gas, listen to your idle. It might know something before you do.

See you next week,

Steve