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An atmosphere of building tension. Apparent is the cold breath exhaled by my competitors as they perform the "about to run" jiggle on the starting line.

A swift flick of the hips.

I'm participating in my local weekly parkrun event and I'm serious. Three, two, one...

Wait a second. I need to sort my watch. As does the guy next to me.

The person in the line expresses impatience. I won't start until… there! Signal acquired, away I go.

During the scramble, it's difficult to see a person without a smartwatch on it. And this isn't only us runners who wear them.

We're witnessing a booming, multi-billion pound sector. Companies like Apple Watch lead the market, each with an broad selection of different models to suit a spectrum of budgets. Based on how feature-packed the watch you select, costs can start from a hundred pounds to thousands of pounds.

"It drives me insane, I can't stop checking."

"It provides solace… It feels like a supporter supporting me."

"I wish it wouldn't say I've experienced a restless night."

A small sample of the responses I've had from other device users when I ask what they their opinion is on theirs.

A Sea of Statistics

My current opinion on mine? At this moment, irritating. It's reporting I'm not hitting my target, causing me to question whether the trees I'm passing under are disrupting my satellite signal.

Millions of us strap these little gadgets onto our wrists and use them all day and night, seemingly comfortable with the fact they're continuously monitoring us.

A distant memory are the days when we relied on them only to give us an estimation of our step count. Currently, they can analyse our sleep quality, stress levels, oxygen saturation, our VO2 max.

It's difficult to find a bodily function they don't track.

But do they do what they claim to do? And are the data points we obsess over a accurate representation of our actual health? Do they enhance our overall health, or do the avalanche of metrics and constant notifications just increase our sense of overwhelm?

A Love-Hate Relationship

"I find myself getting a bit obsessed with mine," a wearer reveals.

While she loves how her device records her exercise, she finds some of its other capabilities "excessive" at times - a feeling initially realised during a significant period.

Until she found out she could change its configuration, her smartwatch kept telling her she was not being productive enough. Now, the watch keeps telling her she's had a poor sleep score.

"I have a young baby, I don't need to be informed I've not slept," she says. "That fact is all too clearly."

Couldn't she just stop wearing it?

"It's possible, theoretically, but I have this complicated dynamic with it," she explains. "I appreciate it for its exercise data, I sometimes question whether the myriad other functions it can now do is perhaps overkill for me."

The Technology Behind the Tracking

Each model of smartwatch has its own unique way of monitoring your health metrics and interpreting your data, but the majority use sensors on the underside of the watch.

They commonly project minute LED lights onto your skin which can monitor capillary action, detecting your BPM. Sophisticated devices analyse changes in the skin conductance that flows through the skin to assess your recovery state.

A Fine Balance

A data scientist says that overall for smartwatches, it's a "delicate equilibrium" - while the continuously improving tech could actually aid early diagnosis, "detecting disease before we notice anything", it could also turn us the tracked into the "anxious healthy".

He points out that newer wearables can carry out tests like electrocardiograms (ECGs), which regularly monitor how stable the heart is. They can flag if someone is experiencing an irregular rhythm, where there is abnormal impulses in the heart causing an irregular heartbeat.

This does not automatically signal someone is imminently going to suffer a cardiac event, but it can give an preliminary indication they might be more at risk of a heart problem in the long term.

But how to interpret these readings is not straightforward. The expert fears that as further capabilities are added, people may struggle to fully understand their data.

"I remain sceptical that being able to monitor so much data is such a beneficial thing," he says.

A clinical psychologist studying cardiology concurs. Her work into the influence of wearable tech on a cohort of cardiovascular patients suggested a minority of those who were given devices to monitor their cardiac function experienced heightened worry and were "far more likely to use medical services".

She noted a pattern with her patients - they noticed a worrying figure on their watch. They grew concerned. Their BPM went up. They got increasingly anxious. They checked again, and their reading went up again.

"Upon viewing stats about ourselves that we lack context for then, understandably, we are going to want to know more," the psychologist says. "We monitor, we re-check - it becomes a feedback loop."