As fitness trackers like the Fitbit Air become better and better, they are now remarkably good at finding new things to measure.
Open the companion app after a workout or a night’s sleep and you'll be greeted by a dizzying array of stats: steps, heart rate, HRV, sleep stages, VO2 max, calories burned, and many more besides.
Some of that information is genuinely useful, but a lot of it is better treated as (interesting) background noise.
The trick is knowing which numbers can tell you something meaningful about your activity or recovery — and, just as importantly, which ones you can actually do something with.
For most of us, though, that leaves a much shorter list than the dashboard might suggest.
Steps still matter
With all the newer metrics available, step count can feel almost quaint, but it remains one of the most useful numbers going, simply because it offers a clear picture of how much you’re moving during the day.
There’s no need to treat 10,000 steps as a magic target, either. Research suggests health benefits begin well below that figure, with more movement generally bringing greater benefits.
Your own baseline is the best place to start. If you typically manage, say, 4,000 steps per day, regularly getting closer to 6,000 is meaningful progress.
Step counting is also one of the things fitness trackers do reasonably well. It won’t tell you how hard you exercised, which we’ll come to next, but it’s an easy way to spot whether a desk-heavy week has turned into a sedentary one.
Track how hard you’re moving
Step count tells you how much you’ve moved, but it says little about intensity. A brisk walk can add the same number of steps as a much slower one while placing very different demands on your body.
Active minutes help fill in that gap. Most trackers estimate how much time you spend at moderate or vigorous intensity, giving you a clearer sense of whether your week includes enough purposeful exercise alongside general movement.
For reference, the World Health Organization recommends at least 150 minutes of moderate-intensity aerobic activity each week — or 75 minutes at vigorous intensity — with more activity bringing additional benefits.
Heart rate zones can also be useful during individual workouts, giving you a quick way to check whether an easy session stayed easy.
Watch your resting heart rate and HRV
Resting heart rate is one of the simpler recovery metrics to understand, showing how many times your heart beats per minute when you’re at rest. Regular aerobic training can gradually bring that number down over time.
Where fitness trackers excel is showing you the trend. A sudden rise above your usual range can sometimes line up with poor recovery or an illness, while a gradual decline can be a sign that your cardiovascular fitness is improving.
Heart rate variability, or HRV, adds more context by measuring the variation in time between heartbeats and can be useful for spotting changes in recovery. It's worth noting that HRV is highly individual, so try not to compare scores.
Focus on better sleep, not a better sleep score
Sleep tracking is most useful when you keep it simple: start with how long you’re actually sleeping and whether your bedtime and wake-up time are reasonably consistent from one day to the next.
Those numbers are easier to interpret than the detailed breakdowns many trackers now provide. Consumer wearables estimate sleep stages from signals such as movement and heart rate, so it’s worth being cautious about treating every minute of deep or REM sleep as exact.
The same goes for proprietary sleep scores; they can be handy as a quick summary, but the underlying habits are usually more useful to watch over time.
I've sometimes found that a low sleep score can trick my brain into thinking I had a bad sleep, which then makes me feel worse, whereas a similar sleep without a tracker leaves me feeling well-rested. Too much information can, in some cases, be a bad thing.
Use VO2 max to track the bigger picture
VO2 max gives you an estimate of how effectively your body can use oxygen during exercise, which makes it a useful shorthand for aerobic fitness.
Most watches calculate it from workout data rather than measuring it directly, so the figure on your wrist won’t be as precise as a laboratory test.
That doesn’t make it useless. If you keep using the same device, the direction of travel can still tell you plenty. For example, a VO2 max score rising over several months indicates improving aerobic fitness.
It’s another metric where the trend is more valuable than the exact number. Whether your watch says 45 or 47 matters less than where that figure is heading over time.
The numbers you can mostly ignore
Plenty of other fitness tracker stats can still be interesting, but they don’t all deserve the same attention.
Calories burned are a good example: estimates can vary considerably between devices, making them a shaky basis for deciding how much to eat or whether you’ve “earned” an extra snack.
Readiness, recovery, and sleep scores can be useful shortcuts, although they’re usually built from the underlying measurements we’ve already covered, so treat them as context rather than definitive judgements.
A good fitness tracker can measure an enormous amount. The trick is learning which numbers actually help you make better decisions – and letting the rest fade into the background.
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