How accurate are wearable fitness trackers? Less than you might think

The rise of wearable fitness trackers has transformed the way we approach our physical health and wellbeing. But, are these devices as accurate as they claim to be? In this article, we’ll explore the results of a recent umbrella review, examining the scientific literature on the accuracy of consumer wearable devices.

A brief history of the quantified self

Back in 2010, Gary Wolf, then the editor of Wired magazine, delivered a TED talk called “the quantified self.” It was about what he termed a “new fad” among tech enthusiasts, where early adopters were using gadgets to monitor everything from their physiological data to their mood, and even the number of nappies their children used.

Wolf acknowledged that these people were outliers – tech geeks fascinated by data – but their behaviour has since permeated mainstream culture.

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A modern obsession with quantification

From smartwatches that track our steps and heart rate, to fitness bands that log sleep patterns and calories burned, these gadgets are now ubiquitous. Their popularity is emblematic of a modern obsession with quantification – the idea that if something isn’t logged, it doesn’t count.

At least half the people in any given room are likely wearing a device, such as a fitness tracker, that quantifies some aspect of their lives. Wearables are being adopted at a pace reminiscent of the mobile phone boom of the late 2000s.

But can wearables truly measure what they claim to?

However, the quantified self movement still grapples with an important question: can wearable devices truly measure what they claim to?

Along with my colleagues, I recently published an umbrella review examining the scientific literature on whether consumer wearable devices can accurately measure metrics like heart rate, aerobic capacity, energy expenditure, sleep, and step count.

Surface-level results

At a surface level, our results were quite positive. Accepting some error, wearable devices can measure heart rate with an error rate of plus or minus 3%, depending on factors like skin tone, exercise intensity, and activity type.

They can also accurately measure heart rate variability and show good sensitivity and specificity for detecting arrhythmia, a problem with the rate of a person’s heart beat.

Additionally, they can accurately estimate cardiorespiratory fitness, which is how the circulatory and respiratory systems supply oxygen to the muscles during physical activity.

However, things become more complex when it comes to more nuanced measures like energy expenditure and sleep quality.

Discrepancies and challenges

Discrepancies were larger for energy expenditure, with error margins ranging from -21.27% to 14.76%, depending on the device used and the activity undertaken.

Results weren’t much better for sleep. Wearables tend to overestimate total sleep time and sleep efficiency, typically by more than 10%. They also tend to underestimate sleep onset latency and wakefulness after sleep onset. Errors ranged from 12% to 180%, compared to the gold standard measurements used in sleep studies.

The challenges of wearables research

Conducting and synthesising research in this field is a challenging endeavour. One hurdle we encountered was the inconsistent methodologies employed by different research groups when validating a given device.

This lack of standardisation leads to conflicting results and makes it difficult to draw definitive conclusions about a device’s accuracy. A classic example from our research: one study might assess heart rate accuracy during high-intensity interval training, while another focuses on sedentary activities, leading to discrepancies that can’t be easily reconciled.

What does it mean for you?

Perhaps most importantly, the rapid pace at which new wearable devices are released exacerbates these issues. With most companies following a yearly release cycle, we and other researchers find it challenging to keep up.

By the time a study is published, the device under investigation is likely to already be obsolete, replaced by a newer model with potentially different specifications and performance characteristics.

Conclusion

As wearable technologies continue to permeate various facets of health and lifestyle, it is important to approach manufacturers’ claims with a healthy dose of scepticism. Gaps in research, inconsistent methodologies, and the rapid pace of new device releases underscore the need for a more formalised and standardised approach to validation of devices.

The goal is to foster collaborative synergies between formal certification bodies, academic research consortia, popular media influencers, and the industry, so that we can augment the depth and reach of wearable technology evaluation.

FAQs

Q: How accurate are wearable fitness trackers?

A: Our results showed that wearable devices can measure heart rate with an error rate of plus or minus 3%, depending on factors like skin tone, exercise intensity, and activity type. However, for more nuanced measures like energy expenditure and sleep quality, discrepancies were larger and more varied.

Q: What are the biggest challenges in wearables research?

A: Conducting and synthesising research in this field is challenging due to inconsistent methodologies, varying sample sizes, and the rapid pace of new device releases. This makes it difficult to draw definitive conclusions about a device’s accuracy and hinders the development of reliable, evidence-based wearables.

Q: What does the future hold for wearable technology evaluation?

A: Efforts are underway to establish a collaborative network that can foster a richer, multifaceted dialogue between formal certification bodies, academic research consortia, popular media influencers, and the industry. This would aim to develop a more formalised and standardised approach to validating wearables, ensuring they are not just innovative gadgets, but reliable tools for health and wellness.