Recovery
Every article on this answers with the same undifferentiated list: stress, sleep, alcohol, overtraining, illness. True, and not much use. The causes are not equally likely, and each one leaves a different fingerprint in your data.
First, check it is actually low — low against your own baseline, not against a chart, and for more than one night. If it is, the answer is usually near the top of this list: a hard session in the last 72 hours, alcohol, a short or late night, an infection arriving, or a steep calorie deficit. One low morning is noise. A week below baseline with a rising resting heart rate is a message.
Most people who ask this question do not have low HRV. They have an ordinary value that looks low next to someone else’s, or one bad morning in an otherwise normal week.
Absolute HRV varies several-fold between healthy adults of the same age and sex. Genetics, resting heart rate, body position, breathing rate, measurement time and the algorithm your device uses all shift it. There is no number you should be hitting. The only meaningful question is how far today sits from your own 30 to 60 day baseline, and whether it has stayed there.
Two rules before you go looking for a cause:
By far the most common answer, and it is not a problem. A genuinely hard session — heavy lifting, intervals, a long run — suppresses HRV for one to three days. That is the adaptation happening. Fingerprint: the dip follows a session you can point to, and it recovers on its own.
The most reliable HRV killer there is. Even moderate drinking suppresses HRV and raises resting heart rate for 24 to 48 hours, and wrecks deep sleep on the night itself. Fingerprint: a sharp drop the morning after, both numbers moving together, and a clean recovery within two days.
Sleep is when the parasympathetic system does its work, so less of it means less variation. Going to bed two hours late does this even at normal duration. Fingerprint: the dip matches a short or late night, and a normal night fixes it.
HRV often falls a day or two before you feel ill, which is the one case where it genuinely earns its keep as an early warning. Fingerprint: a drop with no training or drinking to explain it, usually with resting heart rate clearly up and often respiratory rate too.
Widely missed, because no recovery wearable can see your food. Sustained under-eating is a real physiological stress: it raises resting heart rate and suppresses HRV in a pattern indistinguishable from overtraining. People in a hard diet phase routinely conclude they are overtrained when they are under-fuelled. Fingerprint: a slow, sustained decline over weeks rather than a sharp dip, in step with a diet that started around the same time.
Work pressure, an argument, a deadline, travel and anxiety all lower HRV, sometimes sharply. Fingerprint: a dip with no physical cause, often on a Monday or before something you are dreading.
Digestion and stimulants both keep the sympathetic system engaged into the night. Fingerprint: a modest dip after a late dinner or an evening coffee, gone the next day.
Real under-recovery is a sustained depression, not a single dip. Three to four weeks below baseline, with a resting heart rate that has drifted up and performance that has stopped improving, is the actual overtraining picture. Fingerprint: weeks, not days.
Before blaming your body, rule out the device. A different position, a different time of day, a loose strap, deeper breathing or switching between an overnight average and a two-minute seated reading will all change the number. Fingerprint: the dip coincides with something changing about how you measured, not how you lived.
Persistently low HRV is associated with sleep apnoea, thyroid problems, diabetes, cardiac conditions, depression and some medications including beta blockers and antidepressants. This belongs at the bottom of the list by frequency, not by importance.
Nothing here is exotic, and none of it works overnight:
See someone if your HRV has been well below baseline for several weeks with no training, alcohol or diet explanation, particularly alongside a resting heart rate that has climbed and stayed up, unexplained breathlessness, chest discomfort, dizziness, or heavy daytime sleepiness that suggests sleep apnoea. HRV is not a diagnostic instrument, but a persistent unexplained change is a reasonable thing to mention.
Most of the causes on this list are invisible to a recovery wearable, because they are things you did rather than things your pulse recorded. NutriMacro keeps your HRV and resting heart rate next to the sessions you logged and the calories you actually ate, so a two-week decline can be matched against the diet phase or the training block that produced it. It reads from Apple Health, Google Fit, Health Connect and Samsung Health.
Low means low against your own baseline, not against a chart. Healthy adults of the same age can differ several-fold, so there is no universal threshold. A useful working definition is several consecutive days more than about 10 to 15 percent below your own 30 to 60 day average, especially if your resting heart rate has risen at the same time.
A sudden single-night drop is almost always alcohol, a hard session in the previous 72 hours, a short or late night, or a late heavy meal. If none of those apply and your resting heart rate is up too, an infection is the next most likely explanation. A single drop with a flat resting heart rate is usually just noise.
Acute causes clear quickly: alcohol in one to two days, a hard session in one to three, a bad night in one. Raising your baseline is slower. Consistent sleep, sensible training load and adequate food typically show up over four to eight weeks, and there is no way to shortcut it.
Not on its own. HRV falls after any hard session, which is normal adaptation. What points to genuine under-recovery is a sustained depression of three to four weeks combined with a rising resting heart rate, stalled or declining performance, poor sleep and low motivation. A single metric cannot make that call.
Yes. A steep or prolonged deficit is a genuine physiological stress that raises resting heart rate and suppresses HRV, in a pattern that looks exactly like overtraining. It is frequently missed because recovery apps cannot see food intake. If your HRV has declined slowly over weeks and you are dieting hard, look at your calories before you cut training.
Yes. HRV reflects autonomic state generally, not just physical load. Work pressure, anxiety, travel and emotional stress all suppress it, sometimes as much as a hard session. If the numbers do not match anything physical, this is usually the explanation.
Half the causes of a low HRV are things a wearable cannot see — the session you did, the drinks on Friday, the deficit you have been running for a month. NutriMacro puts all of that on the same screen as the number itself.
NutriMacro is a nutrition and training tracker for iPhone and Android. It logs food by barcode, photo or search, counts food in slices and units rather than grams, and keeps strength training, GPS activities, sleep and recovery in the same daily view. It runs in the language of your phone across 108 countries.
Read next: What is a good HRV? HRV vs resting heart rate What is a recovery score?
