HRV is a readout of how recovered your body is, so you improve it by recovering better, not by chasing the number. Here is what moves it, roughly in order of how much and how well it is documented.
1. Sleep, at a consistent time
Nothing else comes close. Short sleep lowers next day HRV, and inconsistent bed and wake times lower it even when the total is fine, because the body’s clock never settles. Target a bedtime that varies by less than an hour across the week. Sixteen scores consistency separately from duration for exactly this reason.
2. Alcohol
Alcohol in the evening is the most reliable single way to lower overnight HRV, and the effect is dose dependent. Many people first see it in their own data as the pattern: Friday drinks, Saturday red. The fix is the obvious one. Even moving the last drink earlier helps, because the body has more of the night to clear it.
3. Training load, in the right dose
Easy aerobic exercise raises baseline HRV over weeks. Hard sessions lower it for a day or two, and that is normal; it is the adaptation happening. The problem is stacking hard days without the easy ones. Plews and colleagues describe using the seven day rolling HRV average to steer training: when the average sits in or above your normal band, push; when it drops below, back off. Sixteen does this by turning recovery into a strain target each morning.
4. Slow breathing
Breathing at around six breaths a minute, for five to ten minutes, raises HRV acutely and, practised daily, appears to raise the resting baseline in several trials. It is the one lever you can pull on demand. Sixteen’s breathe session is built around this, and it doubles as the way to unlock a short break from your app locks.
5. Evening light and screens
Bright light and stimulating content late in the evening delay sleep onset and shorten sleep, which drags HRV the next morning. It is an indirect effect, but a reliable one. A fixed screen curfew is one of the highest return habits for the effort, which is why Sixteen can lock distracting apps on your sleep schedule.
6. Heat, hydration, illness
Dehydration and heat lower HRV. Illness lowers it before you feel symptoms, which is one of the more useful things a nightly reading tells you. Neither is a training problem; treat them as what they are.
How to know it is working
Ignore single days. Watch the seven day average and the normal band around it. A change that works shifts the average up and narrows the band over three to four weeks. Log the change in your journal so you can see it against the trend rather than guess.
What not to do
Do not chase HRV with cold plunges, supplements or gadgets before you have fixed sleep timing and alcohol. Do not compare your number with anyone else’s. And do not use it to decide anything medical.
Sources
- Plews DJ, Laursen PB, Stanley J, Kilding AE, Buchheit M. Training adaptation and heart rate variability in elite endurance athletes. Sports Medicine, 2013.
- Lehrer PM, Gevirtz R. Heart rate variability biofeedback: how and why does it work? Frontiers in Psychology, 2014.
- Shaffer F, Ginsberg JP. An overview of heart rate variability metrics and norms. Frontiers in Public Health, 2017.
