Holmer flags WHOOP data where sleep regularity moved the numbers
Resting heart rate fell and HRV rose across 38,838 app users, and sleep duration did not change at all.
Brady Holmer flagged a WHOOP study in which 38,838 users of the wearable did four habits for 31 days. The habits were morning light, a 12 hour eating window, zone 2 exercise (easy aerobic running, the conversational stuff) and five minutes of breathwork.
Sleep duration (how long people slept) didn’t change at all!
the thing that best explained these physiological benefits was an improvement in sleep consistency/ regularity
Across that month, resting heart rate fell and HRV rose. HRV is heart rate variability, the beat to beat variation that wearables use as a rough marker of recovery. Holmer writes that the thing which best explained those changes was an improvement in sleep consistency, meaning how regular the sleep and wake times were rather than how much sleep people banked.
And the number that gets the attention is the one that did not move. Sleep duration stayed flat.
What it actually means
Our read is to treat this as a signal, not a finding. It is one company's app data on people who opted into four habits at the same time, which means there is no way to separate the morning light from the zone 2 work from the breathwork from the earlier bedtime. If someone tells you this study proves morning sunlight lowers your resting heart rate, the study cannot say that. It also cannot say that sleep length does not matter, only that in this group sleep length did not change while other things did.
The people who sign up for a 31 day habit challenge inside a recovery app are also not a random sample of runners. They are already motivated, already tracking, and already paying attention to their numbers.
What is useful for a runner here is the framing Holmer leads with. When you do things matters. Going to bed and waking at roughly the same time is free, it does not add training stress, and it is the one variable in that list of four that most people in marathon build could actually fix this week without changing a single session.
So if your resting heart rate has been creeping up and your HRV has been ugly through a big block, the honest version of this is that the fix may not be more hours in bed. It may be the same hours, at the same time, every night. That is a hypothesis worth testing on yourself, and it is not proof.
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