You check your smartwatch after a run. Your fitness score has dropped. You\u2019ve burnt hardly any calories. Your recovery score is really low. It\u2019s telling you to take the next 72 hours off exercise.<\/p>\n
The worst bit? The whole run felt amazing. <\/p>\n
So why\u2019s your watch telling you the opposite?<\/p>\n
Ultimately, it\u2019s because smartwatches and other fitness trackers aren\u2019t always accurate.<\/p>\n
Smartwatches can shape how you exercise<\/p>\n
Using wearable fitness technology, such as smartwatches, has been one of the top fitness trends for close to a decade<\/a>. Millions of people<\/a> around the world use them daily.<\/p>\n These devices shape how people think about health and exercise. For example, they provide data about how many calories you\u2019ve burnt, how fit you are, how recovered you are after exercise, and whether you\u2019re ready to exercise again.<\/p>\n But your smartwatch doesn\u2019t measure most of these metrics directly. Instead, many common metrics are estimates. In other words, they\u2019re not as accurate as you might think.<\/p>\n 1. Calories burned<\/p>\n Calorie tracking is one of the most popular features on smartwatches. However, the accuracy leaves a lot to be desired.<\/p>\n Wearable devices can under- or overestimate energy expenditure (often expressed as calories burned) by more than 20%<\/a>. These errors also vary between activities. For example, strength training<\/a>, cycling<\/a> and high-intensity interval training<\/a> can lead to even larger errors.<\/p>\n This matters because people often use these numbers to guide how much they eat.<\/p>\n 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.<\/p>\n 2. Step counts<\/p>\n Step counts are a great way to measure general physical activity, but wearables don\u2019t capture them perfectly.<\/p>\n Smartwatches can under-count steps by about 10%<\/a> 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.<\/p>\n For most people, this isn\u2019t 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.<\/p>\n 3. Heart rate<\/p>\n Smartwatches estimate your heart rate using sensors that measure changes in blood flow through the veins in your wrist.<\/p>\n This method is accurate at rest or low intensities, but gets less accurate as you increase exercise intensity<\/a>.<\/p>\n 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.<\/p>\n This can be problematic for people who use heart rate zones<\/a> to guide their training, as small errors can lead to training at the wrong intensity.<\/p>\n Read more: 4. Sleep tracking<\/p>\n Almost every smartwatch on the market gives you a \u201csleep score\u201d and breaks your night into stages of light, deep and REM sleep.<\/p>\n 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.<\/p>\n This means they can detect when you\u2019re asleep or awake reasonably well<\/a>. But they are much less accurate at identifying sleep stages<\/a>.<\/p>\n So even if your watch says you had \u201cpoor deep sleep\u201d, this may not be the case.<\/p>\n Read more: 5. Recovery scores<\/p>\n Most smartwatches track heart rate variability and use this, with your sleep score, to create a \u201creadiness\u201d or \u201crecovery\u201d score.<\/p>\n 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<\/a>.<\/p>\n 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.<\/p>\n As a result, if your watch says you\u2019re not recovered, you might skip training \u2013 even if you feel good (and are actually good to go).<\/p>\n 6. VO\u2082max<\/p>\n Most devices estimate your VO\u2082max \u2013 which indicates your maximal fitness. It\u2019s the maximum amount of oxygen your body can use during exercise.<\/p>\n The best way to measure VO\u2082max involves wearing a mask to analyse the amount of oxygen you breathe in and out, to determine how much oxygen you\u2019re using to create energy.<\/p>\n But your watch cannot measure oxygen use. It estimates it based on your heart rate and movement.<\/p>\n But smartwatches tend to overestimate VO\u2082max<\/a> in less active people and underestimate VO\u2082max in fitter ones<\/a>. <\/p>\n This means the number on your watch may not reflect your true fitness.<\/p>\n What should you do?<\/p>\n While the data from your smartwatch is prone to errors, that doesn\u2019t 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.<\/p>\n It\u2019s 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.<\/p>\n","protected":false},"excerpt":{"rendered":"You check your smartwatch after a run. Your fitness score has dropped. You\u2019ve burnt hardly any calories. 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\n What are heart rate zones, and how can you incorporate them into your exercise routine?<\/a><\/p>\n
\n How do sleep trackers work, and are they worth it? A sleep scientist breaks it down<\/a><\/p>\n