What your training numbers actually mean.

Wearables hand you a dashboard and no instructions. Here is which numbers carry information, which are noise, and what beats all of them.

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Trends, not readings

Almost every mistake people make with a wearable comes from reading one day as a verdict. These numbers move with sleep, alcohol, a late meal, a hot room, a cold coming on and where the strap sat. A single figure tells you close to nothing. Fourteen days of the same figure drifting one way tells you a great deal. Judge everything below on its own trend, against your own baseline, and ignore other people entirely.

Heart rate variability, honestly

HRV is the variation in time between heartbeats, and higher generally reflects a nervous system in a recovered state. The catch is that healthy values span roughly 20 to 200 milliseconds between individuals, and depend on the device, the algorithm and the time of night measured. There is no good number to hit. Comparing your HRV to a friend is meaningless; comparing this week to your own last month is not. A sustained drop alongside heavy training, poor sleep or illness is the signal worth acting on.

Resting heart rate, the most useful number on the watch

It is simple, it is measured well even by cheap devices, and it moves with fitness. Trained endurance athletes commonly sit in the 40s. What matters more than the absolute figure is the jump: a resting heart rate 5 to 10 beats above your own baseline for a couple of mornings usually means illness, poor sleep, alcohol, or accumulated training you have not recovered from, and it often shows up before you feel it.

Readiness and recovery scores

These are proprietary blends, usually of HRV, resting heart rate, sleep and recent load, and no two companies compute them the same way. Treat one as a prompt to check in with yourself, not as a verdict on the day. If the score is poor and you feel fine, train and see. If the score is poor and you also feel heavy, unmotivated and sore, that agreement is worth respecting.

What a wrist can and cannot tell you about sleep

Total sleep time from a wrist tracker is reasonably close for most people. The stage breakdown, the deep and REM percentages people fret over, is an estimate from movement and heart rate and it is the weakest part of the report. Use the total and the consistency of your bedtime; do not chase a deep sleep percentage. Sleep is also the largest single lever on everything else here, which is why it appears first in the next section.

What beats every number on the dashboard

In roughly this order: sleep, enough total food, protein spread through the day, gradual increases in training load, and iron status if you are menstruating or training heavily. Unexplained fatigue with dropping performance is worth a blood test before it is worth a supplement, because low ferritin and thyroid problems both present exactly that way. No tub of powder outperforms sleeping an hour more.

When a number means see a doctor

Chest pain, chest pressure or tightness during effort, fainting or near-fainting while exercising, breathlessness out of proportion to the work, or a heart rate that races or stays high long after you stop. None of these are training problems. Stop and get assessed rather than adjusting your program around them.

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If you are buying a fitness tracker

Step count and resting heart rate are the two numbers that matter, and any major-brand band tracks both well. You do not need the expensive model to walk more.

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Common questions

What is a good HRV?

There is no universal good value. Healthy people span roughly 20 to 200 milliseconds depending on age, genetics, the device and the algorithm, so a number that would be excellent for one person is unremarkable for another. What is meaningful is your own trend over two weeks or more, measured the same way each night. A steady drift down alongside hard training, short sleep or a run-down feeling is the signal; one low morning is noise.

Is a low resting heart rate always a good sign?

Usually it reflects fitness, and a trained endurance athlete sitting in the 40s is expected. It is not automatically good, though. A low rate combined with dizziness, fainting, unusual breathlessness or fatigue can point to a conduction problem and deserves a doctor. Context decides: low and feeling strong is fitness, low and feeling faint is a symptom.

Are sleep trackers accurate?

Partly. Total sleep time and bedtime consistency are reasonably reliable on modern wrist devices. The stage breakdown is an estimate built from movement and heart rate, and it disagrees with laboratory sleep studies often enough that chasing a deep sleep percentage is not a good use of your attention. Use the total, use the consistency, ignore the pie chart.

Should I skip training when my readiness score is low?

Not automatically. Treat the score as a prompt to check in rather than an instruction. If you feel fine, start the session and judge it in the first ten minutes. If the score is low and you also feel heavy, unmotivated, sore beyond normal or are sleeping badly, that agreement between the number and your body is worth respecting with an easier day.

What is VO2 max, and does the estimate on my watch mean anything?

VO2 max is the maximum oxygen your body can use during hard effort, and it is one of the strongest single predictors of long-term health. The figure on a watch is an estimate from your heart rate and pace, so the absolute number can be several points off a laboratory test. As a trend over months, in the same conditions, it is genuinely useful for seeing whether your training is working.

Why has my performance dropped for no reason?

The common causes are unglamorous: not enough sleep, not enough total food, too fast an increase in training load, or an unaddressed iron deficiency, which is particularly common in menstruating and endurance athletes. Thyroid problems and recent viral illness also fit the picture. Sustained unexplained decline with fatigue is worth a conversation with a doctor and a blood test, not a new supplement.

Written by the AskDoc Medical Team and reviewed under our Medical Director, MBBS. Health education, not a personal prescription.