Contrast

Resting heart rate

EstablishedMeasured the same way in published research, with results you can compare against.
How Resting heart rate is measuredno differenceclearabout the samenot enough nights yet
How a difference is reported: the estimate, and the 90% range it likely falls in. Crossing zero is not called clear.
What it is
Apple Watch's daily resting heart rate: your 28-day median and how it has moved, and whether it differs on days after a session.
How it is measured
Read from Apple Health. The median of your last 28 days is set against the 28 days before and, when there's a year of data, the same weeks last year, because resting heart rate is seasonal. Changes under 2 bpm are shown as steady. Days after a session are compared with other days once each has at least 5 in the last 90 days.
How to read it
For most adults, 60–100 bpm is normal, and very active people can sit well below 60. In large studies, each 10 bpm higher was associated with about 9% higher risk of death from any cause.
What it cannot tell you
Fitness, sleep, stress, illness, alcohol, the season and medication all move resting heart rate, and one person in five has a week that swings by 10 bpm. A change while using Contrast doesn't show that contrast therapy caused it; a review found little evidence either way.

Sources

Every one of these ships inside the app, with the finding written out so you do not have to open the paper to know why it is there.

  1. Zhang D, Shen X, Qi X. Resting heart rate and all-cause and cardiovascular mortality in the general population: a meta-analysis. CMAJ, 2016.

    46 studies of about 1.25 million people: each 10 bpm higher resting heart rate was associated with 9% higher all-cause and 8% higher cardiovascular mortality.

    doi.org/10.1503/cmaj.150535

  2. Quer G, Gouda P, Galarnyk M, Topol EJ, Steinhubl SR. Inter- and intraindividual variability in daily resting heart rate. PLoS One, 2020.

    Resting heart rate is lowest in July and highest in January, and 20% of people had at least one week that swung by 10 bpm or more.

    doi.org/10.1371/journal.pone.0227709

  3. American Heart Association. All about heart rate (pulse).

    A resting heart rate of 60 to 100 bpm is normal for most adults; active people can be as low as 40.

    www.heart.org/en/health-topics/high-blood-pressure/the-facts-about-high-blood-pressure/all-about-heart-rate-pulse