How come your graphs do not go below a resting heart rate of 70? If you look at <a href="http:&#x2F;&#x2F;www.cdc.gov&#x2F;nchs&#x2F;data&#x2F;nhsr&#x2F;nhsr041.pdf" rel="nofollow">http:&#x2F;&#x2F;www.cdc.gov&#x2F;nchs&#x2F;data&#x2F;nhsr&#x2F;nhsr041.pdf</a>, about half the population should be below that.<p>The only explanations I can think of are either that Apple Watch owners are a non-representative sample (possibly true. But _that_ non-representative?) or that you do not manage to measure resting heart rate that well (how good is the Apple Watch at measuring heart rate?)