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An atmosphere of nervous excitement. I can see the chilled vapour exhaled by my competitors as they perform the "starting line" shuffle on the start line.

A rapid movement of the hips.

I'm lined up for my local 5km community parkrun and I'm serious. It's almost time...

Oh, hang on. I have to adjust my tracker. As does the runner alongside me.

The person behind us expresses impatience. I won't start until… done! GPS ready, away I go.

During the scramble, it's difficult to see a arm without a fitness tracker on it. And it's not just us runners who wear them.

It's a booming, multi-billion pound market. Companies like Garmin are prevalent, featuring an extensive range of diverse versions to cater to a range of needs. Depending on how feature-packed the watch you select, price tags can start from £100 to a small fortune.

"I find it infuriating, I can't stop checking."

"It reassures me… It feels like a supporter supporting me."

"I wish it wouldn't say I've had a bad night's sleep."

Just some of the comments I've received from like-minded tracker enthusiasts when I question what they their opinion is on theirs.

The Monitoring Conundrum

My thoughts on my own device? At this moment, frustrating. It's telling me I'm off pace, leading me to doubt whether the trees along my route are interfering with my location tracking.

Millions of us fasten these compact gadgets onto our arms and keep them on 24/7, apparently unconcerned with the fact they're perpetually monitoring us.

A distant memory are the days when we relied on them exclusively to give us an idea of our pedometer reading. Today, they can track our nightly rest, heart rate, oxygen saturation, our recovery score.

It's a challenge to find a health indicator they fail to monitor.

But do they do what they advertise? And are the data points we scrutinise a accurate representation of reality? Do they boost our overall health, or do the avalanche of metrics and motivational messages just increase our sense of overwhelm?

A Complicated Bond

"I find myself getting a quite fixated with mine," one user admits.

While she appreciates how her device records her runs, she finds some of its other features "overwhelming" at times - a feeling that became apparent during a pregnancy.

Until she found out she could change its configuration, her smartwatch constantly alerted her she was failing to be active enough. Now, the watch insists her she's had a bad night's sleep.

"I have a infant, I don't need to be told I'm tired," she says. "I know that all too clearly."

Why doesn't she just remove it?

"I suppose I could, theoretically, but I'm in this complicated dynamic with it," she continues. "I love it for its workout tracking, I sometimes question whether the myriad other functions it can now do is perhaps excessive for me."

The Technology Behind the Tracking

Every device of smartwatch has its own proprietary way of monitoring your health metrics and interpreting your data, but the majority use optical sensors on the reverse of the watch.

They typically shine small, green LED lights onto your wrist which can detect pulsation, detecting your BPM. Higher-end devices analyse changes in the skin conductance that runs through the skin to gauge your stress levels.

Expert Perspectives

A data scientist says that for most people for smartwatches, it's a "fine balance" - while the continuously improving tech could realistically aid early diagnosis, "identifying issues before we notice anything", it could also turn us the tracked into the "worried well".

He points out that the most advanced wearables can carry out tests like electrocardiograms (ECGs), which constantly monitor how healthy the heart is. They can alert if someone is experiencing an irregular rhythm, where there is irregular electrical activity in the heart causing an arrhythmia.

This does not necessarily indicate someone is imminently going to suffer a cardiac event, but it can give an preliminary indication they might be more susceptible of a blood clot in the future.

But how to make sense of these readings is not straightforward. The expert concerns that as further capabilities are introduced, people may struggle to fully contextualise their data.

"I have some doubts that being able to monitor so many metrics is such a good idea," he says.

A clinical psychologist specialising in cardiology echoes this sentiment. Her work into the impact of wearable tech on a specific group of heart condition patients suggested a noticeable percentage of those who were given devices to monitor their condition experienced heightened worry and were "had a higher tendency to use doctor's time".

She observed a pattern with her patients - they spotted a alarming metric on their watch. They became worried. Their BPM rose. They got more worried. They re-examined the data, and their reading went up again.

"If we see data about ourselves that we can't properly interpret then, understandably, we are going to seek clarification," the psychologist says. "We look, we check again - it becomes a self-fulfilling prophecy."