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A sense of feeling of anticipation. Visible is the cold breath emanating from my fellow runners as they do the "starting line" shuffle on the beginning point.

A rapid flick of the hips.

I'm lined up for my local 5km community parkrun and I'm focused. The countdown begins...

Oh, hang on. I have to adjust my tracker. So does the guy alongside me.

The person in the line expresses impatience. I'm not moving until… there! Signal acquired, I'm off.

In the mele, it's hard to see a wrist without a wearable on it. And it's not just us runners who wear them.

It's a thriving, multi-billion dollar market. Names like Garmin lead the market, all offering an extensive array of diverse versions to cater to a spectrum of lifestyles. Depending on how advanced the model you select, prices can vary between £100 to a small fortune.

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

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

"Please don't notify me I've had a bad night's sleep."

A handful of the reactions I've received from like-minded smartwatch wearers when I ask what they think of theirs.

A Sea of Statistics

My feelings on my own device? Currently, irritating. It's indicating I'm not hitting my target, making me wonder whether the foliage along my route are interfering with my satellite signal.

A vast number of us fasten these little devices onto our wrists and use them constantly, ostensibly at ease with the fact they're continuously monitoring us.

Gone are the days when we depended on them exclusively to give us an idea of our pedometer reading. Now, they can measure our sleep quality, blood pressure, oxygen saturation, our VO2 max.

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

But do they do what they say they do? And are the numbers we analyse a faithful picture of our actual health? Do they boost our mental and physical wellbeing, or do the multitude of readings and motivational messages just contribute to our everyday anxiety?

A Love-Hate Relationship

"I find myself getting a bit obsessed with mine," one user confesses.

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

Before she realised she could put it into a specific mode, her smartwatch repeatedly informed her she was not being productive enough. In a new phase, the watch insists her she's had a bad night's sleep.

"I am caring for a six-month old, there's no point to be told I've not slept," she says. "I know that perfectly well."

Couldn't she just stop wearing it?

"I suppose I could, perhaps, but I'm in this complicated dynamic with it," she says. "I appreciate 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

Different brands of smartwatch has its own proprietary way of tracking your bodily functions and analysing your data, but the most use optical sensors on the reverse of the watch.

They typically shine minute LED lights onto your skin which can detect capillary action, identifying your pulse rate. Sophisticated devices detect changes in the electrical current that runs through the skin to assess your recovery state.

A Fine Balance

A data scientist says that in general for smartwatches, it's a "delicate equilibrium" - while the continuously improving tech could potentially aid early diagnosis, "identifying issues before we feel unwell", it could also turn us watch wearers into the "worried well".

He points out that the most advanced wearables can perform tests like electrocardiograms (ECGs), which regularly monitor how stable the heart is. They can alert if someone is experiencing a heart arrhythmia, where there is irregular electrical activity in the heart causing an uneven pulse.

This does not automatically signal someone is on the verge of a heart attack, but it can give an early warning they might be more at risk of a blood clot in the years to come.

But how to interpret these figures is not straightforward. The expert concerns that as more functions are introduced, people may find it hard to fully comprehend their data.

"I remain sceptical that the ability to monitor so many metrics is such a beneficial thing," he says.

A professor focusing on patient behaviour agrees. A study into the effect of wearable tech on a cohort of individuals with health issues suggested a significant portion of those who were given devices to monitor their condition experienced increased anxiety and were "had a higher tendency to use doctor's time".

She observed a cycle with her patients - they saw a alarming metric on their watch. They grew concerned. Their heart rate went up. They got increasingly anxious. They checked again, and their reading rose further.

"When people are presented with data about ourselves that we lack context for then, understandably, we are going to become concerned," the psychologist says. "We monitor, we check again - it becomes a self-fulfilling prophecy."