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There's a nervous excitement. Visible is the frosty air exhaled by my rivals as they execute the "about to run" wiggle on the starting line.

A rapid flick of the hips.

I'm at my local 5km community parkrun and I mean business. It's almost time...

Hold on. I must start my device. The same goes for the person next to me.

The person waiting tuts. I won't start until… done! Connection established, away I go.

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

We're witnessing a thriving, multi-billion pound market. Companies like Apple Watch dominate, featuring an extensive selection of diverse models to suit a range of needs. Based on how feature-packed the model you select, price tags can vary between a hundred pounds to a small fortune.

"I find it infuriating, I'm unable to switch off."

"It reassures me… It feels like a companion guiding me."

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

A handful of the comments I've had from like-minded tracker enthusiasts when I question what they their opinion is on theirs.

The Data Dilemma

My thoughts on mine? Right now, irritating. It's telling me my speed is wrong, leading me to doubt whether the overhead branches I'm passing under are blocking my GPS connection.

Millions of us strap these compact devices onto our wrists and use them constantly, apparently unconcerned with the fact they're continuously monitoring us.

Gone are the days when we used them only to give us an estimation of our pedometer reading. Today, they can track our sleep quality, heart rate, glucose levels, our recovery score.

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

But are they able to do what they claim to do? And are the data points we obsess over a faithful picture of our actual health? Do they improve our mental and physical wellbeing, or do the plethora of readings and constant notifications just increase our everyday anxiety?

Addiction or Aid?

"I do get a bit preoccupied with mine," one user confesses.

While she appreciates how her device monitors her runs, she finds some of its other features "daunting" at times - a feeling that became apparent during a significant period.

Before she realised she could change its configuration, her smartwatch kept telling her she was being insufficiently active enough. Now, the watch frequently reports her she's had a restless night.

"I have a six-month old, there's no point to be told my sleep was poor," she says. "I know that perfectly well."

Why doesn't she just take it off?

"It's possible, perhaps, but I have this love-hate relationship with it," she explains. "I love it for its exercise data, I sometimes question whether the additional features it can now do is possibly excessive for me."

How Do They Work?

Each model of smartwatch has its own unique way of measuring your vitals and interpreting your data, but the vast bulk use sensors on the underside of the watch.

They typically project small, green LED lights onto your wrist which can observe pulsation, recording your pulse rate. Sophisticated devices measure changes in the bioimpedance that runs through the skin to gauge your stress levels.

The Professional Viewpoint

A data scientist says that overall for smartwatches, it's a "fine balance" - while the rapidly advancing tech could actually aid early diagnosis, "identifying issues before we show symptoms", it could also turn us device users into the "worried well".

He points out that the most advanced wearables can perform tests like electrocardiograms (ECGs), which constantly monitor how normal the heart is. They can flag if someone is experiencing a heart arrhythmia, where there is irregular signals in the heart causing an irregular heartbeat.

This does not automatically signal someone is on the verge of a heart attack, but it can give an preliminary indication they might be more at risk of a blood clot in the future.

But how to interpret these numbers is complex. The expert fears that as more functions are incorporated, people may find it hard to fully understand their data.

"I'm not entirely convinced that being able to monitor so many things is such a good idea," he says.

A health researcher specialising in patient behaviour echoes this sentiment. Research into the impact of wearable tech on a specific group of individuals with health issues suggested a significant portion of those who were given devices to monitor their heart health experienced heightened worry and were "had a higher tendency to use medical services".

She identified a vicious circle with her patients - they noticed a alarming metric on their watch. They grew concerned. Their heart rate went up. They got even more concerned. They checked again, and their heart rate rose further.

"Upon viewing data about ourselves that we lack context for then, of course, we are going to become concerned," the psychologist says. "We check, we re-check - it becomes a self-fulfilling prophecy."