If you’re among the one in five Americans who wears a fitness-tech device, you’re carrying a veritable gold mine of data on your wrist. As easily as checking the time, it’s possible to record and retrieve just about anything you might want to know about your workouts, activity level, and fitness progress — plus some fitness markers you’ve probably never heard of.
With all this information an arm’s length away, it’s possible to become overwhelmed (or obsessed) with the numbers — and potentially disconnected from your own intuition.
Moreover, these numbers aren’t guaranteed to be accurate. Some markers require more sophisticated technology than is currently offered in most wrist-based wearables. And several investigative news stories and studies have found that wearables’ optical sensors and software algorithms may not provide proper readings from darker skin tones, making some data unreliable for people of color.
Still, it is possible to have a healthy relationship with your wearable device by learning which data markers are most beneficial, what their shortcomings and limitations are, and how they can support — and not supplant — your intuition about your body.
“I think it’s good to look at the data as ‘interesting’ information,” says Christopher Lundstrom, PhD, MEd, lecturer in the University of Minnesota’s School of Kinesiology. “Don’t assume that there’s a problem if, for example, you have walking asymmetry. If you have no pain, no injuries, and you feel fine, then you don’t have a problem, so don’t stress about it.”
“Same goes with your activity level. If your energy is good and you like your routine, that’s great.”
To help you decide what to pay attention to and what to tune out, our experts break down several of the most common fitness markers into three categories.
- Great to know: markers that are the most accurate and can offer important insights for most exercisers.
- Good to know: markers that are less accurate or apply to fewer people.
- Can live without: information that is interesting and potentially promising in future iterations of the technology but is currently less helpful for fitness progress.
That said, it’s up to you to recognize what matters to you individually, based on your unique body and goals.
“My advice is not to let the data become the goal,” Lundstrom adds. “The goal is feeling good and improving your health. This information can help support that, but don’t let the data become too important, or too much of a driver for you.”
Great to Know
Heart Rate
This simple data can tell you how hard you’re working during exercise and daily activities, as well as offer a snapshot of overall cardiovascular health while at rest. “Generally speaking, the more fit you get, the lower your resting heart rate gets,” explains Lundstrom.
Checking heart rate during physical activity can help you gauge whether you need to increase or decrease intensity.
Heart-rate measurements from wearables are pretty accurate, though the data may be less accurate as your heart rate increases, says researcher Michael Snyder, PhD, a genetics professor at the Stanford School of Medicine.
Standing Breaks
Some devices track the number of hours in which you stand and move for at least one minute. This may be a helpful marker, especially if you tend to sit at a desk all day. Certain wearables will even remind you to get up and move around, breaking up long sessions in front of the computer or TV.
Standing still for long periods of time can be just as problematic as sitting, according to a 2015 University of Michigan study. So don’t reduce the goal to just standing still — think of it as moving your body to break up monotonous and sedentary activity. Switch between sitting, standing, and walking around over the course of an hour to avoid prolonged time in any one position.
Active Energy
This measures the calories you burn via daily activity. Many people assume the primary benefit of this marker is to help achieve a calorie deficit for weight loss, but tracking energy offers broader health benefits as well.
Knowing how much energy you’re using can aid you in fueling your body. It can also help you learn how your activity levels vary on different days, in different seasons, and even year over year.
And tracking energy expenditure can connect varying activity levels to other markers like fatigue, hunger, mood, and overall energy, as well.
Many wearables estimate active energy based on your heart rate (a higher heart rate means more energy), weight, age, sex, height, and movement. Accuracy varies by device and activity, according to an analysis.
Good to Know
Heart-Rate Variability
Tracking the time between heartbeats measures your heart-rate variability (HRV). The more variation there is, the greater your fitness and resilience to stress; less variation can signal low fitness, high stress levels, and illness.
HRV measurements from wearables are pretty accurate, according to Snyder, and this data can help you track changes in fitness and stress. A gradual increase indicates improvements, whereas a decrease could mean you’re overworking or ailing, Lundstrom explains.
Steps
Tracking the number of steps you walk may help you increase your physical activity beyond structured workouts. But instead of aiming for a specific number, “look at the trends and see where you feel good,” Lundstrom says. Find that sweet spot and aim to meet it as often as possible.
Many wearables register steps as your arms swing, so step counts can be off by as much as 20 percent, Snyder notes: An activity that involves your arms (like brushing your teeth) can add extra steps.
Conversely, you may miss out on steps if one arm doesn’t swing while you walk — as with pushing a stroller or shopping cart.
Average Walking Speed
Fitness devices use your step length to calculate how long it took you to travel a set distance. This is otherwise known as your average walking speed.
Tracking your average walking speed over time can help you gauge fitness improvements. For example, if it takes you 20 minutes to cover a mile one week and only 18 minutes at the same intensity a few weeks later, you’ve progressed.
Can Live Without
VO2 Max
This measure of the maximum amount of oxygen your body uses during intense exercise is considered the best indicator of cardiovascular fitness, Snyder says.
Unfortunately, wearables can only estimate based on other markers, such as age, heart rate, and activity levels. To get an accurate reading, visit a lab or health club equipped to analyze the air you exhale during exercise.
Step Length
Stride or step length is a measure of the distance you cover with every step. Tracking this can aid runners trying to keep their strides at an optimal length, Lundstrom says. It can also be a helpful long-term marker to track age-related mobility changes.
That said, there’s no such thing as a perfect step length, and wrist-based devices may lack accuracy, says Snyder.
Rather than worry about this data, it’s more useful to consistently train balance, leg strength, and core stability that will ultimately help you take full, confident steps that suit your body.
Double Support Time
This is the percentage of time you spend with two feet on the ground while walking: A lower double support time number generally means you walk more with your weight on one foot instead of two, signaling an imbalance.
A higher percentage is preferable, but — as with step length — rather than worry about numbers, it’s more helpful to put your energy and attention toward training activities that support and boost balance.
Walking Asymmetry
A measure of balance and coordination, walking asymmetry reveals the percentage of time that your steps with one foot are faster or slower than the other foot. If you have a healthy walking pattern, the timing of your steps will be similar.
Higher walking asymmetry can indicate limping, which may be a sign of injury, disease, or imbalance. But it usually won’t reveal a hidden condition; rather it will reflect one. Again, training balance and coordination can help maintain or improve walking symmetry.
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