Technology and Fitness Tracking
Around one in three adults in the UK now wears a fitness tracker. The global wearables market was worth $78 billion in 2024. And yet research on whether these devices actually improve health outcomes is more nuanced than the marketing suggests. A 2022 Lancet review of 39 studies found that people using wearable activity trackers took an average of 1,800 more steps per day and walked 40 more minutes than non-trackers. That's a genuine, meaningful behaviour change. But the same data also showed diminishing returns over time, and other studies have found that obsessive tracking can generate anxiety that actually reduces motivation in some users.
The honest picture: fitness technology is a useful tool for some people and largely irrelevant noise for others. Whether it helps you depends almost entirely on whether you use the data to change behaviour — and which data you choose to focus on.
The metrics that actually matter
Not all the numbers on your wrist are created equal. Some wearable metrics are well-validated, genuinely informative, and directly linked to longevity outcomes. Others are marketing features with limited scientific basis. Understanding the difference is probably the most useful thing this page can offer.
Resting heart rate is one of the most reliable metrics a consumer wearable can provide. Wearables measure it accurately, and the data is clinically meaningful — a chronically elevated resting heart rate is associated with higher cardiovascular risk, reduced fitness, and incomplete recovery. More practically: if your resting heart rate is consistently 8 or more beats above your personal baseline for two or more days, your body is telling you something. Trends across weeks and months tell the real story.
Heart rate variability (HRV) has been covered in the recovery page. Consumer wearables measure it reasonably well, and its value as a recovery and stress indicator is well-evidenced. The key is to compare your numbers to your own baseline — not to population averages. An HRV of 35 ms is meaningless in isolation. An HRV of 35 ms when your 30-day average is 55 ms is a clear signal to rest.
Weekly active minutes is arguably the single most actionable longevity metric available on any wearable. It directly measures whether you're hitting the evidence-based threshold of 150+ minutes of moderate-intensity activity per week. Most people who think they're hitting this target discover they're not when they actually track it. Closing that gap matters more than any other number your device shows you.
Sleep duration and consistency are tracked reliably by most modern devices. Total sleep time and bedtime consistency — going to bed and waking at roughly the same time — are both strongly linked to health outcomes and worth monitoring across weeks. They're imperfect but directionally accurate.
The metrics worth treating with scepticism
VO2 max estimates from consumer wearables are the headline longevity feature that every device now promotes. The reality is more complicated. A large meta-analysis found that wearables overestimate VO2 max by up to 15% during resting-based tests. Exercise-based algorithms are more accurate but still carry meaningful margins of error. More significantly, wearables tend to overestimate in less fit individuals and underestimate in highly fit ones — the two cases where accuracy matters most.
This doesn't mean the feature is useless. The direction of your VO2 max trend over months is meaningful — if it's rising, you're getting fitter; if it's declining, something has changed. But treating the absolute number as precise enough to compare to the mortality risk tables in published research overstates what consumer devices can actually deliver. If you want an accurate VO2 max reading, a treadmill or cycle test with proper equipment is the only reliable method.
Sleep stages — the REM, deep, and light breakdowns — are among the least accurate consumer wearable measurements. Multiple validation studies comparing wearables to clinical polysomnography find poor accuracy in stage classification, even from premium devices. How you feel on waking is often a more reliable indicator of sleep quality than the stage percentages on your app.
Calorie burn estimates from wearables can be off by 20–40%. Using these numbers to justify eating more is one of the most common ways trackers actively undermine health goals. The data is not accurate enough to support nutritional decision-making.
The 10,000 steps target — present on almost every device — originated as a marketing slogan for a Japanese pedometer in 1964, not a clinical recommendation. More recent research suggests health benefits begin to plateau at around 7,000–8,000 steps daily for older adults, and that the intensity of movement matters more than the count. A 20-minute brisk walk scores better for longevity markers than 10,000 ambling steps.
The data anxiety problem
One finding from the research that rarely appears in device marketing: for some people, continuous tracking increases health anxiety rather than improving behaviour. The effect varies significantly between individuals. People who are already motivated and use data to guide decisions tend to benefit. People who are prone to perfectionism or health anxiety can find that constant monitoring amplifies worry without improving outcomes.
If you notice that checking your tracker first thing in the morning regularly affects your mood or generates preoccupation, that's worth acknowledging. A tracker that makes you anxious is not helping you live longer. Taking periodic breaks — a week without wearing it — can recalibrate your relationship with the data and reveal whether the device is serving you or you're serving it.
Choosing a device — what actually matters
For the 45–65 age group with longevity as the primary goal, a device that accurately tracks resting heart rate, HRV, sleep duration, and active minutes covers the key bases. That describes most mid-range devices from established manufacturers.
Continuous glucose monitors (CGMs) — small sensors worn on the arm that track blood sugar in real time — are worth mentioning as a distinct category. They're increasingly available without prescription and give genuinely useful insight into how different foods, meals, exercise timing, and sleep affect metabolic function. For people managing or at risk of type 2 diabetes, or simply curious about their metabolic response to diet, a two-week trial can be revealing in ways that conventional wearables can't match.
'The most useful thing a tracker can tell you is whether you actually hit 150 minutes of moderate activity this week. Most people think they did. Many discover they didn't. That gap, closed consistently over months, is where the longevity benefit lives.'
The tool is only as good as what you do with it
The Lancet data that showed 1,800 more daily steps in tracker users is real — but it also showed that the effect diminished over time for many participants. The device doesn't change behaviour on its own. The insight it provides has to be acted on, and acted on repeatedly, for months and years.
The most effective use of a fitness tracker is as a feedback loop: measure, notice a gap between intention and reality, adjust, remeasure. Not as a score to maximise, a competition to win, or a source of anxiety to manage. Used that way, the technology genuinely adds something. Used as a substitute for thinking about what your body needs, it's an expensive step counter.
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