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Six ways your smartwatch is lying to you, according to science

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Six ways your smartwatch is lying to you, according to science

You check your smartwatch after a run. Your fitness score has dropped. You’ve burnt hardly any calories. Your recovery score is really low. It’s telling you to take the next 72 hours off exercise.

The worst bit? The whole run felt amazing.

So why is your watch telling you the opposite?

Ultimately, it’s because smartwatches and other fitness trackers aren’t always accurate.

Smartwatches can shape how you exercise

Using wearable fitness technology, such as smartwatches, has been one of the top fitness trends for close to a decade. Millions of people around the world use them daily.

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These devices shape how people think about health and exercise. For example, they provide data about how many calories you’ve burnt, how fit you are, how recovered you are after exercise, and whether you’re ready to exercise again.

But your smartwatch doesn’t measure most of these metrics directly. Instead, many common metrics are estimates. In other words, they’re not as accurate as you might think.

1. Calories burned

Calorie tracking is one of the most popular features on smartwatches. However, the accuracy leaves a lot to be desired.

Wearable devices can under- or overestimate energy expenditure (often expressed as calories burned) by more than 20 per cent. These errors also vary between activities. For example, strength training, cycling and high-intensity interval training can lead to even larger errors.

This matters because people often use these numbers to guide how much they eat.

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For example, if your watch overestimates calories burned, you might think you need to eat more food than you really need, which could result in weight gain. Conversely, if your watch underestimates calories burned, it could lead you to under-eat, negatively impacting your exercise performance.

2. Step counts

Step counts are a great way to measure general physical activity, but wearables don’t capture them perfectly.

Smartwatches can under-count steps by about 10 per cent under normal exercise conditions. Activities such as pushing a pram, carrying weights, or walking with limited arm swing likely make step counts less accurate, as smartwatches rely on arm movement to register steps.

For most people, this isn’t a major problem, and step counts are still useful for tracking general activity levels. But view them as a guide, rather than a precise measure.

3. Heart rate

Smartwatches estimate your heart rate using sensors that measure changes in blood flow through the veins in your wrist.

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This method is accurate at rest or low intensities, but gets less accurate as you increase exercise intensity.

Arm movement, sweat, skin tone and how tightly you wear the watch can also impact the heart rate measure it spits out. This means the accuracy can vary between people.

This can be problematic for people who use heart rate zones to guide their training, as small errors can lead to training at the wrong intensity.

4. Sleep tracking

Almost every smartwatch on the market gives you a “sleep score” and breaks your night into stages of light, deep and REM sleep.

The gold standard for measuring sleep is polysomnography. This is a lab-based test that records brain activity. But smartwatches estimate sleep using movement and heart rate.

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This means they can detect when you’re asleep or awake reasonably well. But they are much less accurate at identifying sleep stages.

So even if your watch says you had “poor deep sleep”, this may not be the case.

5. Recovery scores

Most smartwatches track heart rate variability and use this, with your sleep score, to create a “readiness” or “recovery” score.

Heart rate variability reflects how your body responds to stress. In the lab it is measured using an electrocardiogram. But smartwatches estimate it using wrist-based sensors, which are much more prone to measurement errors.

This means most recovery metrics are based on two inaccurate measures (heart rate variability and sleep quality). This results in a metric that may not meaningfully reflect your recovery.

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As a result, if your watch says you’re not recovered, you might skip training — even if you feel good (and are actually good to go).

6. VO₂max

Most devices estimate your VO₂max — which indicates your maximal fitness. It’s the maximum amount of oxygen your body can use during exercise.

The best way to measure VO₂max involves wearing a mask to analyse the amount of oxygen you breathe in and out, to determine how much oxygen you’re using to create energy.

But your watch cannot measure oxygen use. It estimates it based on your heart rate and movement.

But smartwatches tend to overestimate VO₂max in less active people and underestimate VO₂max in fitter ones.

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This means the number on your watch may not reflect your true fitness.

What should you do?

While the data from your smartwatch is prone to errors, that doesn’t mean it is completely worthless. 

These devices still offer a way to help you track general trends over time, but you should not pay attention to daily fluctuations or specific numbers.

It’s also important you pay attention to how you feel, how you perform and how you recover. This is likely to give you even more insight than what your smartwatch says.

Hunter Bennett is a lecturer in exercise science at Adelaide University. This piece first appeared on The Conversation.

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Fitness

How the 3-3-3 Rule Helped Me Stick to an Exercise Routine

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How the 3-3-3 Rule Helped Me Stick to an Exercise Routine

If you’ve ever started a new workout routine with the best intentions only to find yourself skipping sessions by week two, you’re not alone. I’m the type to get trapped in the same cycle of burnout, where I go hard for a couple of weeks, feel exhausted, feel guilty, and repeat. For me, what finally broke that cycle wasn’t a new gym membership or a fancy fitness app, but a simple scheduling hack: the “3-3-3 rule.” I’d seen this rule applied it to general productivity, and all the same principles can apply to your fitness habits, too. Here’s how you can use the 3-3-3 rules to structure your workouts and create a habit that sticks.

What is the 3-3-3 rule?

The 3-3-3 “rule” (or “method,” or “gentle suggestion”) is essentially a weekly workout framework built around three types of movement, each done three times per week:

  • Three strength training sessions. This includes lifting weights, bodyweight circuits, resistance bands, whatever builds muscle and challenges your body.

  • Three cardio sessions. This includes running, cycling, swimming, jump rope, a dance class—what counts as “cardio” is up for debate, but here, I think of it as anything that gets your heart pumping.

  • Three active recovery days. This includes light walking, yoga, stretching, foam rolling, and so on.

And yes, I realize this math adds up to nine intentional days of movement across a seven-day week. Here’s the thing: You do double duty some days, or skip workouts here and there, or adjust to a nine-day cycle, because the point isn’t rigid scheduling. The point is rhythm over a strict structure. For me, the 3-3-3 rule provides a sense of momentum that’s flexible enough to fit into real life, but consistent enough to actually stick to.

Why the 3-3-3 rule works for me

Before I get into how the 3-3-3 rule helped me specifically, let’s talk about why so many workout plans fall apart in the first place. I believe most of them make two classic mistakes. The first is doing too much, too soon. You go from zero to six days a week at the gym, you get burnt out, and the whole thing unravels. The second mistake is having no real structure at all—just vague intentions, like “I’ll work out when I can,” which never materializes into anything real for a lot of people.

For me, the 3-3-3 rule solves both of those problems. It gives me enough structure to build habit and momentum, but not so much intensity that my body and brain feel overwhelmed. I personally adore running, but I struggle to motivate myself to lift weights; the 3-3-3 rhythm here helped me find a middle ground between those two workouts. When I know I have three strength sessions to hit in a week (or nine-ish day cycle), I can look at my calendar and find three slots without too much drama or dread.

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There’s also plenty of breathing room built into the plan, which was the biggest game changer for me. I used to have the (toxic) thought that my rest days were wasted days, which is a mentality that led to either overtraining or complete inactivity with pretty much no middle ground.

Plus, there’s something psychologically satisfying about the number three. I know and love the rule of threes in photography, comedy, survival tips, and all over the place.

How to make a 3-3-3 workout schedule work for you

The 3-3-3 rule has a ton of wiggle room for customization. Here are some ideas for how you can approach it:


What do you think so far?

For strength days, pick a format you actually enjoy. That might be a full-body circuit, a push/pull/legs split, or a class at your gym. (Boxing, anyone?) Your focus on these days should be a progressive challenge—push yourself, yes, but don’t obliterate yourself.

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For cardio days, variety helps. Mix a longer, easier effort with a shorter, more intense session (like a 20-minute interval run). I know I’m biased, but cardio really shouldn’t feel like punishment.

For recovery days, resist the urge to “make them count” by sneaking in extra work. The whole point is to let your body consolidate the gains from your harder days. Walk, stretch, breathe, and trust the process.

Another practical tip: Pick a night to map out your 3-3-3 week ahead of time. You’ll probably find that the week arranges itself pretty naturally once you’re looking for those nine windows.

The bottom line

As always, consistency should always be your priority in fitness. If you’ve been struggling to find a rhythm, if your past workout plans have always fizzled out around week three, give the 3-3-3 rule an honest four-week try. Maybe start with a 1-1-1 month! After all, the 3-3-3 rule isn’t a hack to totally transform your physique, but I do think it can provide something way more valuable. Finding a routine that works for you—like the 3-3-3 rule works for me—is the first step to make exercise a reliable, sustainable part of your life.

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I’m a running coach — I’ve just tested shoes actually designed for women’s feet, and they’re a total game changer

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I’m a running coach — I’ve just tested shoes actually designed for women’s feet, and they’re a total game changer

Why you can trust TechRadar


We spend hours testing every product or service we review, so you can be sure you’re buying the best. Find out more about how we test.

QLVR ENDVR: Two minute review

Most running shoes feel familiar for a reason: the formula has barely changed in millennia. We have archaeological evidence of shoes being fastened with “shoelaces” as far back as around 3,500 BC, yet the basic lace-up running trainer remains the default.

QLVR (pronounced “clever”) set out to challenge that. Its debut shoe, the ENDVR, is a laceless “running slipper” built around a women-specific mechanical structure, with a slip-on Wing Fit system inspired by the way a bird’s wing opens and closes around movement.

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Mere minutes of daily vigorous exercise can cut your risk of 8 diseases | CNN

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Mere minutes of daily vigorous exercise can cut your risk of 8 diseases | CNN

Move more. Sit less. For many years, that’s been accepted guidance for people wanting to get healthier.

Now that message is getting refined, with a growing body of research suggesting that certain types of movements may be more beneficial than others when it comes to health benefits.

The intensity of your exercise may matter as well. A new study published in the European Heart Journal found that a small amount of vigorous activity may be linked to lower risk of eight different chronic diseases.

The findings raise questions about why intensity matters and how people can incorporate more intense exercise routines into everyday life. To better understand the study’s implications, I spoke with CNN wellness expert Dr. Leana Wen, an emergency physician and clinical associate professor at George Washington University. She previously served as Baltimore’s health commissioner.

Before beginning any new exercise program, consult your doctor. Stop immediately if you experience pain.

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CNN: What did this study examine about exercise and its relationship to chronic disease?

Dr. Leana Wen: This investigation looked at how the intensity of physical activity is related to the risk of developing a range of chronic diseases. Researchers analyzed data from two very large groups in the UK Biobank, which is a long-term health study in the United Kingdom that tracks medical and lifestyle information from hundreds of thousands of participants. One group included about 96,000 people who wore wrist activity trackers that objectively measured their movement, and the other included more than 375,000 people who self-reported their activity.

The researchers followed participants over an average of about nine years and examined the development of eight conditions: major cardiovascular events, atrial fibrillation, type 2 diabetes, immune-related inflammatory diseases, fatty liver disease, chronic respiratory disease, chronic kidney disease and dementia, as well as overall mortality.

The key finding was that the proportion of activity done at vigorous intensity mattered. People who had more than about 4% of their total activity classified as vigorous had substantially lower risks of developing these conditions compared with people who had no vigorous activity at all. The numbers were stunning, with the participants having the following results:


  • 63% lower risk of dementia,

  • 60% lower risk of type 2 diabetes,

  • 48% lower risk of fatty liver disease,

  • 44% lower risk of chronic respiratory disease,

  • 41% lower risk of chronic kidney disease,

  • 39% lower risk of immune-mediated inflammatory diseases,

  • 31% lower risk of major cardiovascular events,

  • 29% lower risk of atrial fibrillation, and

  • 46% lower risk of death from any cause.

These results are amazing. Imagine if someone invented a medication that could reduce the risks of all these diseases at once — it would be very popular! Crucially, even people who exercised a lot still benefited if the proportion of time they spent doing vigorous physical activity was increased. Conversely, people who were relatively inactive also benefited from adding just a little bit of higher-intensity exercise to their daily routines.

CNN: What counts as “vigorous” physical activity?

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Wen: Vigorous activity is generally defined as exercise that substantially raises your heart rate and breathing. A simple way to gauge it is the “talk test.” If you can speak comfortably in full sentences while exercising, you are likely in the low to moderate range. If you are so out of breath that you can only say a few words at a time, that is vigorous.

Running, cycling, lap swimming or climbing stairs quickly could count. But this also depends on people’s baseline fitness. For some individuals, taking longer strides with walking can be vigorous exercise. Others who are already fairly fit would need to do more. It’s also important to remember that vigorous activity doesn’t have to be in the context of a structured exercise plan. Short bursts of effort in daily life, such as rushing to catch a bus or carrying heavy groceries upstairs, can also qualify if they raise your heart rate and make you breathless.

CNN: Why might higher intensity exercise provide additional health benefits?

Wen: Higher intensity activity places greater demands on the body in a shorter period. This type of movement can improve cardiovascular fitness, increase insulin sensitivity and support metabolic health more efficiently than lower-intensity activity alone. Some studies have also linked vigorous activity with cognitive benefits.

Greater intensity may have distinct benefits across different organ systems. The researchers found that some conditions, such as immune-mediated inflammatory diseases, appeared to be more strongly linked to the intensity of activity than to the total amount. On the other hand, type 2 diabetes and kidney disease were influenced by both how much activity people did and how intense it was. Why this is the case is not yet known, but intensity appears to have a significant impact across diseases affecting multiple organs.

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CNN: How much vigorous activity do people need?

Wen: The threshold for people seeing a benefit appears to be relatively low. The researchers found that once people reached more than about 4% of their total activity as vigorous, their risk of developing chronic diseases dropped substantially.

To put that into practical terms, we are not talking about professional athletes dedicating their lives to hours of high-intensity training. Everyday people may see benefits from just doing a few minutes of vigorous effort daily.

CNN: How can people realistically incorporate vigorous activity into their daily routines?

Wen: One helpful way to think practically is that vigorous activity does not have to happen all at once. It can be accumulated in short bursts throughout the day.

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People can take the stairs instead of the elevator and do so at a faster pace than usual. When they are heading to work, they can add some speed walking. They can park farther away when grocery shopping and walk briskly while carrying groceries.

Structured exercise also can incorporate intervals where people alternate between moderate and more intense effort. If you’re swimming laps, you can warm up at a more leisurely pace, then do a few laps at a faster pace, then again at a leisurely pace and repeat. This suggestion applies to any other aerobic exercise: Aim for multiple intervals of at least 30 seconds to a minute each where your body is working hard enough that you feel noticeably out of breath.

CNN: What about someone who is older or has mobility issues?

Wen: Not everyone can or should engage in high-intensity activity in the same way. Vigorous activity is relative to that person’s baseline. For someone who is not used to exercise, even a short period of slightly faster walking or standing up repeatedly from a chair could be considered high intensity. And not everyone may be able to walk. In that case, some exercises from the chair can have aerobic benefits.

Individuals who have specific medical conditions should consult with their primary care clinicians before embarking on a new exercise routine. People with mobility issues also may benefit from working with a physical therapist who can help to tailor exercises appropriate to their specific situation.

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CNN: What is the key takeaway for people trying to improve their health?

Wen: To me, the main takeaway from this study is that it’s not only how much total exercise you get but also how hard you push yourself that matters. And you don’t have to have a lot of high-intensity exercise: Adding just a little has substantial health benefits across a wide range of chronic health conditions.

At the same time, exercise needs be practical. People should look for opportunities to safely increase intensity in ways that fit their daily lives. The most effective approach to physical activity is a balanced one: Exercise regularly, incorporate more challenging activities when you can and build habits that are sustainable over time.

Get inspired by a weekly roundup on living well, made simple. Sign up for CNN’s Life, But Better newsletter for information and tools designed to improve your well-being.

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