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An atmosphere of building tension. Visible is the frosty air coming from my rivals as they do the "starting line" shuffle on the start line.

A rapid movement of the hips.

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

Hold on. I have to sort my tracker. As does the person beside me.

The person behind us tuts. I refuse to go until… done! Signal acquired, away I go.

During the scramble, it's challenging to see a arm without a fitness tracker on it. And this isn't only us athletes who rely on them.

This is a thriving, massive market. Names like Apple Watch are prevalent, featuring an extensive range of different models to fit a spectrum of budgets. Based on how advanced the watch you choose, prices can range from a hundred pounds to a significant investment.

"I find it infuriating, I'm unable to stop checking."

"It reassures me… It acts as a companion supporting me."

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

A small sample of the responses I've received from other tracker enthusiasts when I ask what they think of theirs.

A Sea of Statistics

My thoughts on mine? Currently, frustrating. It's indicating my speed is wrong, making me wonder whether the foliage I'm passing under are disrupting my satellite signal.

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

A distant memory are the days when we used them exclusively to give us an estimation of our daily steps. Today, they can measure our sleep quality, blood pressure, oxygen saturation, our recovery score.

It's tricky to find a health indicator they aren't designed to measure.

But do they do what they claim to do? And are the statistics we obsess over a true reflection of reality? Do they improve our mental and physical wellbeing, or do the avalanche of measurements and constant notifications just increase our sense of overwhelm?

Addiction or Aid?

"I become a quite preoccupied with mine," one user reveals.

While she values how her device records her workouts, she finds some of its other capabilities "excessive" at times - a feeling that became apparent during a significant period.

Before she realised she could put it into a specific mode, her smartwatch constantly alerted her she was not being productive enough. In a new phase, the watch keeps telling her she's had a poor sleep score.

"I've got a infant, there's no point to be informed I've not slept," she says. "That fact is only too well."

Why doesn't she just stop wearing it?

"It's possible, theoretically, but I have this push-pull dynamic with it," she says. "I appreciate it for its workout tracking, but I'm unsure whether the myriad other functions it can now do is maybe too much for me."

How Do They Work?

Every device of smartwatch has its own proprietary way of measuring your vitals and interpreting your data, but the most use optical sensors on the underside of the watch.

They usually emit minute LED lights onto your arm which can detect pulsation, detecting your heartbeat. More advanced devices analyse changes in the skin conductance that runs through the skin to gauge your recovery state.

The Professional Viewpoint

A data scientist says that overall for smartwatches, it's a "delicate equilibrium" - while the rapidly advancing tech could actually aid early diagnosis, "detecting disease before we feel unwell", it could also turn us device users into the "concerned but fine".

He points out that some of the latest wearables can carry out tests like medical-grade monitoring, which regularly monitor how stable the heart is. They can alert if someone is experiencing an irregular rhythm, where there is abnormal signals in the heart causing an irregular heartbeat.

This does not mean someone is about to have a cardiac event, but it can give an early warning they might be more at risk of a heart problem in the years to come.

But how to interpret these readings is complicated. The expert concerns that as further capabilities are introduced, people may struggle to fully understand their data.

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

A clinical psychologist focusing on patient behaviour echoes this sentiment. Her work into the impact of wearable tech on a cohort of individuals with health issues suggested a significant portion of those who were given devices to monitor their cardiac function experienced increased anxiety and were "far more likely to use doctor's time".

She noted a cycle with her patients - they saw a concerning reading on their watch. They became worried. Their heart rate increased. They got increasingly anxious. They checked again, and their reading increased again.

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