Why track anything at all
Numbers can make an invisible habit visible. If you walk more this month than last month, a record shows it, even when it does not feel like much has changed. Numbers can also help you notice patterns, such as poor sleep after late workouts or a week where everything slipped.
They also have limits. A metric is a measurement of one narrow thing, often an estimate, and it is easy to start chasing the number instead of the thing it stands for. The goal of this guide is to help you pick a few metrics that serve you and to read them with reasonable skepticism.
If you have a heart condition, are pregnant, are recovering from an injury, or have any other health concern, it is sensible to talk with a doctor or other qualified professional before changing your activity level. They can also tell you which numbers matter in your situation.
Steps and daily activity
Step counts are the most familiar number because almost every phone and wearable provides one. They are a rough way to see how much you moved through an ordinary day, including the movement that is not exercise.
A few things are worth knowing:
- The round figure of 10,000 steps is a popular target, but it is a convenient round number rather than a threshold where health suddenly changes. Many people benefit from moving more than they currently do, whatever their starting point.
- Counts differ between devices. A wrist device can register steps when you gesture, and can miss steps when you push a stroller or carry something.
- Steps say little about intensity. A slow stroll and a brisk walk can produce similar counts over a day.
A more practical approach is to find your typical week and nudge it upward gradually. Our piece on daily steps goes into setting a sensible target.
Heart rate
Heart rate is how many times your heart beats per minute. Your resting heart rate, taken when you are calm, tends to vary from person to person for many reasons, including genetics, fitness, medications, caffeine, stress and illness. During exercise it rises with effort.
Many devices estimate heart rate with light sensors on the wrist. These are usually reasonable at steady effort and less reliable during fast changes, such as intervals, or when the band is loose. Chest straps are generally considered more accurate, but they are another thing to wear.
Heart rate becomes more useful when connected to effort. Heart rate zones divide your range into bands, from easy to hard. A common rule of thumb for estimating a maximum is subtracting your age from 220, but this is only an average-based estimate and can be off by a lot for an individual. If a zone number conflicts with how you feel, trust the feeling and consider a simpler check such as the talk test or a scale of perceived exertion. Neither requires a device.
Sleep
Sleep tracking is popular and also among the least precise features on consumer devices. Wearables usually infer sleep from movement and heart rate, so their estimates of sleep stages, in particular, should be treated as rough guesses.
What tends to be more dependable is the broad picture: roughly when you went to bed, when you got up, and how consistent that was across the week. Most adults need somewhere in a typical range of hours, though the right amount varies, and we discuss sleep duration separately. If a tracker tells you that you slept poorly but you feel fine, there is no need to worry. If you feel unwell or exhausted for weeks regardless of the numbers, that is a reason to talk to a doctor, and persistent fatigue is worth taking seriously.
Workout totals and training logs
A different kind of metric is the one you record yourself: how long you exercised, how far you walked, the weight you lifted, how many repetitions you completed. These are often more meaningful than automated estimates because you know exactly what they represent.
Two warnings apply. First, “calories burned” figures from devices and gym machines are estimates and commonly differ from real expenditure, so they are poor guides for deciding how much to eat. Second, more is not always better. If your totals climb every week without any rest days, a number going up may simply mean you are accumulating fatigue.
Body measurements and weight
Body weight, waist and other measurements are slower-moving metrics. Weight can fluctuate by a surprising amount within a single day because of fluid, food and timing, so a single reading says little. Looking at the trend over weeks is generally more informative. Whether to track body measures at all is personal. Some people find them motivating; others find them stressful, and it is fine to skip them. We compare these and other options in the piece on measuring progress.
How to read the numbers sensibly
- Prefer trends to single days. One odd reading is usually noise.
- Pair a number with how you feel. Energy, mood and how hard a session felt are data too.
- Choose a few. Two or three metrics that match your goal beat a dashboard of twenty.
- Stay with one method. Switching devices or methods makes comparisons unreliable.
- Take breaks. If tracking makes you anxious or obsessive, stepping away for a while is reasonable.
Your goal determines your metrics. Someone building a walking habit may only need daily steps, while someone starting a lifting program might do best with a simple log of weights and repetitions. Sorting out what you are trying to achieve first, perhaps using the idea of smart goals, makes the choice of numbers much easier.
A brief summary of limits
No metric measures your health, fitness or worth in full. Devices estimate, bodies vary, and the same number can mean different things for different people. Used lightly, tracking is a helpful mirror. Used rigidly, it can become a source of pressure. Start with the smallest set of numbers that helps you stay consistent, and let the rest go.