Understand what each of Fitbit's health and fitness measurements and scores means.
There are so much fitness and health measurements going on in today’s Fitbits and other activity trackers and smartwatches that you need to be a medical practitioner or personal trainer to understand what these statistics and metrics all mean.
This is especially interesting as Fitbit has now given free access to its Health Metrics dashboard (see below) to all owners of its Sense, Versa 3, Versa 2, Inspire 2 and Charge 4. Previously, this was available only to Fitbit Premium subscribers. Free access is now for 7-day trends, while all Premium members with compatible devices have access to the 7-day and 30-day views.
More than just steps
Long gone are the days when trackers just counted your steps through the day. Quickly new measurements were added, such as floors climbed, distance, and calories burned.
Today, though, fitness trackers and smartwatches have a virtual doctor’s laboratory of tests and health metrics as well as a fitness instructor’s database of your exercise and workout statistics.
Fitbit is keen to point out that its health features “are not intended to diagnose or treat any medical condition and should not be relied on for any medical purposes”, and if you have any concerns about your health, you should talk to a healthcare provider, or, in extreme circumstances, call the emergency services.
Your Fitbit is not your doctor, but you can share its data with your medic.
Instead, Fitbit’s measurements are intended to provide information that can help you manage your general health and well-being.
Many of these Fitbit measurement explanations also work for other fitness trackers and smartwatches, such as those from Apple, Samsung and Huawei.
The top-end Fitbit smartwatches have more health features than the lower-end trackers, but as all the current Fitbits now have a heart-rate sensor there are plenty that apply to all.
To help you choose the right Fitbit, we have rounded up tests and reviews of all the current and recent Fitbits.
First, let’s start with the basics.
Fitbit Steps count
Available on: All Fitbits
The most basic of all activity tracker measurements, Steps are just that: how many steps are you doing each day. From this metric, Fitbit also calculates the Distance you have travelled on foot, if you prefer to set this as your target. 10,000 steps is roughly equal to 4 miles or 7km, depending on the length of your stride.
A Fitbit device uses a 3-axis accelerometer to count your steps, determining the frequency, duration, intensity, and patterns of your movement.
When you track an activity with GPS, your tracker calculates your distance using GPS data rather than steps.
Why it matters: Walking is considered light to moderate exercise, depending on how you do it. It’s a more realistic way to begin getting fitter compared to immediately starting training for a marathon, and it’s easy to motivate yourself to walk more without the need for a personal trainer shouting at you. It’s also cheaper than signing up for 12 months at the gym.
Expected range: The magic number is 10,000, but that doesn’t come from medical analysis but actually dates back to a marketing campaign for a pedometer sold before the 1964 Tokyo Olympic Games. The pedometer was called the Manpo-kei: “man” meaning 10,000, “po” meaning steps and “kei” meaning metre, and 10,000 steps just stuck after that.
What’s really important is setting yourself a realistic target and then incrementally increasing that as you progress.
Also, counting steps isn’t the end goal. Getting fitter involves pushing yourself, and especially your heart, further than you would in a normal day - see later for more on going further than steps.
Actually, the best way I use steps is via the Reminders To Move feature, which motivates you to get up and move every hour for at least 250 steps. Staying sat down is not good for you, and of course you can set the hours you want to be reminded in.
Floors Climbed count
Available on: All Fitbits except the Inspire family
Most Fitbits and activity trackers feature an altimeter that records how high you climb during the day. This needn’t involve a mountain or even a hill, and it’s recorded by Fitbit as “Floors Climbed” as for most of us it will involve using the stairs more than getting in a lift or standing on an escalator.
The altimeter detects when you go up in elevation, registering one floor when you climb about 10 feet or 3 metres. The tracker uses changes in barometric pressure combined with the steps you take to calculate floors climbed.
Why it matters: Taking a hilly route on a walk or run is going to exercise your heart more than on the flat, so it’s an extra motivator to improve your fitness.
What we are looking out for is arrhythmia, which means any change from the normal sequence of the heart’s electrical impulses - which may happen too fast, too slowly, or erratically.
Your pulse is one of the body’s four vital signs, and Fitbit’s heart monitor uses it to gather much information about your level of fitness and wellbeing.
How to read Fitbit's Resting Heart Rate (RHR)
Available on: All Fitbits except Ace 2
Resting Heart Rate is the number of times your heart beats per minute (bpm) when you are still and rested - not to be confused with your heart rate during exercise.
Why it matters: RHR can be an important indicator of your level of fitness and cardiovascular health.
Bradycardia is a heart rate that is too slow: below 50bpm. It can be caused by a number of factors, including: problems with the sinoatrial (SA) node or in the conduction pathways of the heart that don’t allow electrical impulses to pass properly from the atria to the ventricles; low thyroid hormone; or damage from heart disease or heart attack.
A too-slow heart rate can cause insufficient blood flow to the brain, so you might suffer fatigue, dizziness that can lead to fainting (or near-fainting) spells, and shortness of breath.
Tachycardia refers to a resting heart rate that’s too fast: above 100bpm. Remember, this is your resting heart rate - you will likely exceed 100bpm when exercising vigorously, and this is quite different to having a high resting heart rate.
A rapid heartbeat keeps the heart’s chambers from filling completely between contractions, which compromises blood flow to the rest of the body.
Symptoms of tachycardia are, strangely, similar to those of bradycardia, including: fainting, dizziness, shortness of breath, and fatigue. But also palpitations and chest pressure are signs of a too-high resting heart rate.
Expected range: RHR usually ranges from 60-100bpm, but varies according to your age and fitness level. Generally, the lower the better - although too slow is as big a problem as too fast. Current medical advice is that between 50-100bpm is healthy. Physically active adults, such as athletes, often have a resting heart rate slower than 60bpm.
What can help: Factors such as alcohol and caffeine intake, smoking and stress levels, can affect your resting heart rate. Getting fitter should improve your RHR, and, armed with a fitness tracker, you are already equipped to start improving your general heart health.
But you should certainly consult a doctor if you think that your heart rate is too fast or slow, or you are experiencing any of the symptoms listed above.
Available on: Fitbit Sense only
Your heart rate is a key indicator of your health, and Fitbit can keep you informed when it's above or below your threshold when rested or inactive for at least 10 minutes.
When the Fitbit detects your heart rate above or below your personal threshold, you receive a notification on the device (at the moment, just the top-end Sense).
By default, the threshold is between 44 and 120, but you can customise this range in the Fitbit app.
How to read Fitbit's Heart Rate Zones (HRZ)
Available on: All Fitbits with a heart-rate sensor
During workouts, you can get real-time stats on your tracker’s screen to see whether you’re in one of three Heart Rate Zones: starting with Fat Burn, moving to Cardio, and, at best, Peak.
Your target heart rate zones are personalised using your fitness level and your age.
How to read Fitbit's Cardio Fitness Score (VO2 Max)
Available on: All Fitbits with a heart-rate sensor
Fitbit uses a bunch of its and your stats - resting heart rate, weight, age, gender - to give you a Cardio Fitness Score, also known as VO2 Max.
It’s a measurement of your cardiovascular fitness, or how well your body uses oxygen when you are working out at your hardest. The higher your score, the more fit you are.
Traditionally, VO2 Max was measured in a lab as you ran on a treadmill or rode a stationary bike with a mask strapped onto your face gauging the amount of air you inhale and exhale.
Fitbit’s measurement is not going to be as accurate as that method, but it is certainly easier and more comfortable
That you can compare to people of the same age range and gender. You can then use it to motivate yourself to improve your score.
The score can be made more accurate by using either the GPS on your Fitbit (Charge 4, Versa 3, Sense) or connected to your phone on other Fitbits.
Why it matters: The more stationary your lifestyle, the lower your score will be, and the higher your risk of developing high blood pressure and coronary heart disease.
Expected range: Your score is set in six cardio fitness levels from Poor to Excellent.
What can help: Get moving and exercise more. Healthy weight loss – lowering your body fat percentage – will also lower your score. Moderate exercise is a great start, but moving onto interval training will really boost your score.
How to read Fitbit's Active Zone Minutes (AZM)
Available on: Sense, Versa series, Ionic, Charge 4, Inspire 2
Active Zone Minutes replaced Fitbit’s Active Minutes by combining with the Heart Rate Zones. The tracker will buzz your wrist when you enter each personalised target heart rate zone, and add up your AZM per day and per week. You earn 1 zone minute in the Fat Burn zone, but 2 in Cardio or Peak zones, so turn that brisk walk into a run to earn more AZM.
Why it matters: You will get fitter if you exercise your heart harder, so these are more meaningful targets to set yourself.
Expected range: The World Health Organization and the American Heart Association recommend 150 minutes of moderate activity or 75 minutes of vigorous activity per week. You can adjust your weekly goal in the Fitbit app.
How to read Fitbit's Heart Rate Variability (HRV)
Available on: All Fitbits with a heart-rate sensor.
Requires Fitbit Premium
Heart rate variability is the variation of time between each heartbeat. Even if your heart rate is 60bpm, it doesn’t mean that your heart is beating in a regular pattern each second.
It is a measure of your autonomic nervous system - widely considered one of the best objective metrics for physical fitness.
Two branches of the nervous system compete by sending simultaneous signals to the heart. The parasympathetic branch (“rest and digest”) handles inputs from internal organs, and causes a decrease in heart rate. The sympathetic branch (“fight or flight”) responds to stress and exercise, and increases your heart rate.
If your nervous system is balanced, your heart is constantly being told to beat slower by your parasympathetic system, and beat faster by your sympathetic system. This causes a fluctuation in your heart rate: HRV.
You can view your nightly average (in milliseconds) and trends over time in the Health Metrics dashboard, but this is available only to Premium subscribers.
Why it matters: A higher HRV is seen as healthier, while a drop in HRV could indicate that you are experiencing stress or showing potential signs of illness.
What can help: You can improve your HRV through hydration, a healthier diet, and quality sleep.
How to read Fitbit Sleep Score and Sleeping Heart Rate (SHR)
Available on: All Fitbits with a heart-rate sensor
SHR displayed only via Fitbit Premium
Your heart rate should slow down during sleep, except when you are having a bad dream – or maybe a very good one.
Fitbit uses your Sleeping Heart Rate as part of its Sleep Score in the Restoration section (rating how peaceful or agitated you were during sleep). Sadly, only Premium subscribers can see SHR in detail, although the total Sleep Score is available to all.
Fitbit’s Sleep Score measures not just the duration of your sleep but the sleep quality, and also shows you how much time was spent in the three Sleep Stages: Light, Deep and REM.
Fitbit splits your scores into three groups, totalling 100: Time Asleep gets up to 50 points; Time in Deep and REM sleep gets a possible 25 points; and Restoration another 25 points.
Why it matters: Poor sleep is linked to higher body weight, and sleep is involved in healing and repair of your heart and blood vessels, and improving your immune system. Sleep deficiency is linked to an increased risk of heart disease, kidney disease, high blood pressure, diabetes, and stroke - as well as depression. Was we all know, a good night's sleep can improve concentration and productivity the following day. Deep and REM sleep can help you unlock the restorative power of sleep.
What can help: As with improving your resting heart rate, exercising more, reducing stress and losing weight are helpful. Fitbit helps here with mindfulness tools and help in weight loss programs through exercise and calorie counting. But swap exercise for a guided breathing session just before bed, as exercise will increase your body temperature, which isn’t great for improving your sleep.
Increase the duration of sleep by going to bed earlier. Limit alcohol three hours before bedtime since it can suppress REM sleep.
How to read Fitbit's Estimated Oxygen Variation
Requires Fitbit Premium
You find this graph under the Restoration tab in your Sleep Score.
It is normal for blood oxygen saturation to fluctuate, but high variations can suggest breathing issues. Factors that affect blood oxygen saturation include altitude, heart and lung health and breathing disturbances during sleep.
Why it matters: Look out for symptoms such as excessive tiredness, loud. snoring, and gasping during sleep.
How to read Fitbit's Breathing Rate (BR)
Available on: All Fitbits with a heart-rate sensor
Requires Fitbit Premium
Breathing Rate - also known as Respiratory rate - is one of the body’s vital signs. It is different from Resting Heart Rate. It’s the number of breaths you take each minute in order to get enough oxygen into your body.
Fitbit automatically measures your breathing rate while you sleep. It’s looking for signs of significant changes.
You can view your nightly average and trends over time in the Health Metrics dashboard, but only if you subscribe to the Fitbit Premium service.
Why it matters: Breathing rate can be affected by your weight, lung and heart conditions, anxiety and fever. Among the conditions that can change a normal respiratory rate are asthma, anxiety, pneumonia, congestive heart failure, and lung disease.
Expected range: Typical breathing rate is 12-20 breaths per minute. A respiration rate under 12 or over 25 breaths per minute, while resting, is considered abnormal.
What can help: Regular exercise can increase the strength and function of your muscles, which will then require less oxygen to move and will produce less carbon dioxide. This will reduce the amount of air you need to breathe in and out.
Also helpful: breathing exercises, increasing your vitamin D intake and singing. And see if you can improve the air quality in your home by keeping house plants.
How to read Fitbit's Skin Temperature
Available on: Fitbit Sense (with or without Premium) and Ionic and Versa series smartwatches; Charge 4 "coming soon".
The top-end Fitbit smartwatches feature a sensor that tracks your skin temperature each night to show how it varies from your personal baseline (set over three nights when you first setup the watch), so you can be aware of your trends over time.
Why it matters: Variation is normal from night-to-night, and can be caused by changes in room temperature, bedding and a woman’s menstrual cycle. But it can also be an indication of the onset of fever.
The temperature reading doesn’t show on the watch itself, only in the Fitbit app - and it displays only variation, not your actual temperature.
Fitbit Sense users can see their Skin Temperature variation on the Today screen of the Fitbit app. Other Fitbit smartwatch users need to subscribe to Fitbit Premium to see the data in the Health Metrics dashboard (see later).
How to read Fitbit's Oxygen Saturation (SpO2)
Available on: Any Fitbit smartwatch and the Charge 4.
Your bloodstream must be able to carry oxygen throughout the body. SpO2 is the level of oxygen in your blood.
SP stands for serum pressure and O2 is oxygen. It is a measure of the amount of oxygen affixed to hemoglobin cells within the circulatory system.
You can see your SpO2 nightly average and range on wrist with a special SpO2 clock face on your Fitbit smartwatch, and view trends over time on the app with Fitbit Premium.
Also see Estimated Oxygen Variation aove.
Why it matters: Our body needs oxygen to obtain energy to fuel all our living processes, and 90% of our energy comes from oxygen. Oxygen is the most important nutrition of our cells, every function in our body is dependent on oxygen, and it is the power for our body and muscles.
A low score may be an indication of important changes in your fitness and wellness. Hypoxaemia is an abnormally low amount of oxygen in the blood. Symptoms include headache, shortness of breath, rapid heartbeat, coughing, and confusion.
Expected range: Fitbit measures SpO2 above 80%, and a healthy score would be above 95%.
What can help: Get more fresh air, drink more water, eat more iron-rich food, exercise more, and train your breathing using Fitbit's guided breathing sessions.
How to read Fitbit's Electrodermal Activity Scan (EDA)
Available on: Fitbit Sense only
Only Fitbit Premium members see their score breakdown.
During high levels of 'emotional arousal' such as stressful states, sweat secretion is intensely activated, which can be measured. The Sense uses a multi-path electrical sensor to detect electrodermal activity responses on your skin that may indicate your stress levels.
Fitbit adds in other physiological measurements such as skin temperature and HRV to create an algorithm that can distinguish a negative from a positive response.
The EDA Scan app measures this while you are doing an EDA mindfulness session.
See Stress Management below.
How to read Fitbit's Stress Management Score
Available on: Fitbit Sense only
Why it matters: Stress is how your body and mind react to various situations - positive and negative - caused by hormones released from your autonomic nervous system (ANS). The stress responses that result from ANS activity can show up as physical signs of stress. Chronic stress over time can harm your mental and physical health.
Expected range: Fitbit Sense users see a daily Stress Management Score in the Fitbit app ranging from 1 to 100 - where a higher number means you’re showing fewer physical signs of stress. It’s calculated based on three metrics: your Responsiveness (score out of 30), Exertion Balance (score out of 40) and Sleep Patterns (score out of 30).
To understand ANS and Responsiveness, Fitbit looks at: Heart Rate Variability (HRV), Elevated Resting Heart Rate (RHR), Sleeping Heart Rate above RHR, and Electrodermal Activity (EDA).
On Exertion, Fitbit takes into account: Daily Steps, Weekly Activity, and Fitness Fatigue Score.
For Sleep Patterns, Fitbit scores you for: Sleep debt over time, Restlessness, and REM and Deep Sleep duration the night before.
What can help: Clinical studies show that mindfulness-based practice, such as meditation, is effective at reducing stress. Fitbit has several mindfulness tools, such as guided breathing sessions, and other Premium-only programs and content.
How to read Fitbit's Electrocardiogram (ECG)
Available on: Fitbit Sense only
The ECG app on the Fitbit Sense can assess your heart for atrial fibrillation (AFib), a heart rhythm irregularity.
You place your index finger and thumb on the sensors hidden in corners of the watch for less than a minute.
The app cannot detect your heart rhythm when not in use.
Why it matters: During AFib, the upper chambers of the heart contract irregularly, increasing the risk of heart attack, blood clots, stroke and other heart conditions.
AFib can be difficult to detect, so having the Fitbit ECG app to test your heart rhythm from your wrist gives you a better chance of spotting it.
What can help: While Fitbit’s ECG assessment can’t diagnose AFib on its own, you can share its results with your doctor.
How to use Fitbit's Menstrual Health Tracking
Available on: All Fitbits with a heart-rate sensor, except the Ace 2
You can use the Fitbit app to log periods, record symptoms, predict future periods, estimate your fertile window and ovulation day, and other information related to your cycle.
This isn't automatic, and requires you to log most of the data yourself.
The predictions are estimated using an algorithm that includes the period and cycle length information provided by the user. If you don’t provide some of the information about your cycle, Fitbit uses a 28-day cycle and 5-day period as a starting point for estimations.
Why it matters: By having all of your health and fitness data in one place and looking at it over time, you can discover the impact your menstrual cycle has on your overall health, and better understand connections between your activity, sleep, and cycle symptoms.
It can help you recognize any recurring irregularities and help you identify menstrual patterns linked to everyday activities like sleep and exercise.
Fitbit is keen to highlight that this feature is not intended to be used for contraceptive or other medical purposes.
Fitbit Weight measurement
As clever as your Fitbit tracker is, strapped to your wrist it cannot weigh you. But it is a major weapon in your weight-loss program - motivating you in your exercise regime and informing you as you reach your movement and heart-rate targets.
But on your Fitbit app’s Today screen is a card for Weight. You can manually log your weight, or save yourself the effort by investing in the Fitbit Aria air scales (£49.99 / US$49.95) that sync with the app.
The Aria Air measures just your weight and, synced, lets the Fitbit app calculate your Body Mass Index (BMI). If you want more metrics, you need a smarter scale - such as Fitbit’s previous scale, the Aria 2, which measured your body fat percentage using bioelectrical impedance analysis.
As the Aria 2 is no longer available, you could get a lot more weight-related stats by buying a smarter set of digital scales, such as the Withings Body Cardio that measures your weight and a bunch of body composition stats (body fat, water percentage, muscle and bone mass).
For fuller explanations of all these body/weight measurements (BMI, Body Fat, etc), read our feature on the best digital smart scales.
How to read Fitbit's Health Metrics Dashboard
Requires Fitbit Premium for full 7-day trend and 30-day trend access; free dashboard access for 7-day trends for Sense, Versa 3, Versa 2, Inspire 2 and Charge 4.
Fitbit's Health Metrics dashboard is available to Premium subscribers only, although it shows some for non-Premium users. It displays five health metrics so you see the trends in your overall wellbeing.
After wearing a Fitbit tracker or smartwatch during sleep, Premium members will see nightly averages and graphs on there.
It's strangely dull in colour compared to some of the graphs on the Fitbit app, and we'd prefer Fitbit to show all these stats to non-Premium users, too.
If you aren't subscribed to Fitbit Premium, Versa 3 users can still see their SPO2 and Resting Heart Rate data, but not Breathing Rate, Heart Rate Variability or Skin Temperature.
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