Resting Heart Rate: What Moves It

Resting heart rate is the oldest fitness number there is, and a wearable now measures it every night without anyone counting a pulse. Most of what moves it comes down to two things: how much blood the heart moves with each beat, and how hard the nervous system is leaning on it.

What lowers it

Aerobic training makes the heart a bigger, stronger pump. Each beat moves more blood, so fewer beats are needed at rest. At the same time the parasympathetic side of the nervous system, the brake, gains the upper hand over the accelerator. The result is a resting heart rate that drifts down over months of consistent training. It commonly falls by several beats within a few months of starting, and endurance athletes commonly sit in the 40s and 50s.

The general adult range is about 60 to 100 beats per minute. In large cohorts a resting heart rate above about 80 goes with higher rates of heart disease and death than one in the 60s. That is an association, not proof, but the fitness that lowers it is protective.

What raises it

Anything that puts the body under load tends to show up here early.

• Illness. A fever raises resting heart rate by roughly 10 beats for each degree Celsius, often before symptoms start.
• Alcohol. A few drinks in the evening raise overnight heart rate by several beats, in proportion to how much was drunk.
• Poor sleep. A short or broken night leaves the accelerator engaged, and the next night's number tends to run high.
• Hard training without enough recovery. Several days in a row above baseline, with legs that feel flat, is the pattern of someone who needs an easier week.
• Heat, dehydration, a late large meal, caffeine late in the day and stress all nudge it up as well.

Less commonly, a resting heart rate that climbs and stays up with no obvious reason points at something medical: an overactive thyroid, anemia, or an infection that has not declared itself. That is worth a lab draw, not a bigger training load.

Trends, not nights

A single night tells you very little, because the number moves with every item on that list. The useful reading is your own baseline, the average over the last few weeks, and how far tonight sits from it. One night 5 beats high after a late dinner is noise. Three nights in a row 5 beats high with no drinks involved is information.

Over months the direction of the baseline is the report card. A line that drifts down across a training block says the heart is adapting.

We read members' overnight heart rate alongside their labs, their training plan and their VO2 test, because the trend in that one number often shows whether the plan is working before anything else does.

This article is educational and is not medical advice.

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