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A sense of feeling of anticipation. Visible is the frosty air coming from my fellow runners as they execute the "starting line" wiggle on the starting line.

A rapid movement of the hips.

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

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

The person behind us tuts. I'm not moving until… there! GPS ready, and I'm running.

In the mele, it's challenging to spot a person without a fitness tracker on it. And this isn't only us participants who use them.

This is a thriving, multi-billion dollar market. Companies like Garmin lead the market, all offering an extensive selection of different models to suit a range of lifestyles. Depending on how advanced the device you go for, costs can vary between £100 to thousands of pounds.

"It drives me insane, it's impossible to stop checking."

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

"Please don't notify me I've had a restless night."

A handful of the responses people have shared from other device users when I question what they feel about theirs.

The Data Dilemma

My current opinion on my own device? At this moment, annoying. It's indicating I'm not hitting my target, leading me to doubt whether the overhead branches I'm running below are blocking my GPS connection.

A vast number of us fasten these compact gadgets onto our arms and use them constantly, ostensibly unconcerned with the fact they're constantly monitoring us.

Gone are the days when we depended on them solely to give us an rough count of our pedometer reading. Now, they can analyse our nightly rest, blood pressure, heart rate variability (HRV), our VO2 max.

It's a challenge to find a health indicator they don't track.

But can they do what they claim to do? And are the numbers we scrutinise a faithful picture of reality? Do they boost our overall health, or do the plethora of readings and cheerleading alerts just increase our sense of overwhelm?

Addiction or Aid?

"I become a bit preoccupied with mine," a wearer confesses.

While she loves how her device tracks her exercise, she finds some of its other functions "daunting" at times - a feeling first discovered during a pregnancy.

Before she realised she could change its configuration, her smartwatch kept telling her she was being insufficiently active enough. In a new phase, the watch frequently reports her she's had a poor sleep score.

"I've got a six-month old, it's unnecessary for me to be told I've not slept," she says. "I know that all too clearly."

Why doesn't she just remove it?

"I could, theoretically, but I'm in this push-pull dynamic with it," she explains. "I value it for its workout tracking, but I'm unsure whether all the other things it can now do is maybe overkill for me."

The Technology Behind the Tracking

Different brands of smartwatch has its own novel way of tracking your vitals and analysing your data, but the majority use detectors on the underside of the watch.

They typically emit tiny, coloured LED lights onto your wrist which can observe pulsation, identifying your heartbeat. Higher-end devices measure changes in the electrical current that passes over the skin to get an idea of your nervous system activity.

The Professional Viewpoint

A data scientist says that for most people for smartwatches, it's a "fine balance" - while the rapidly advancing tech could realistically aid early diagnosis, "identifying issues before we show symptoms", it could also turn us watch wearers into the "concerned but fine".

He points out that the most advanced wearables can perform tests like medical-grade monitoring, which constantly monitor how stable the heart is. They can alert if someone is experiencing atrial fibrillation (AF), where there is erratic signals in the heart causing an arrhythmia.

This does not automatically signal someone is about to have 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 interpret these figures is not straightforward. The expert worries that as additional features are incorporated, people may not be able to fully contextualise their data.

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

A clinical psychologist studying patient behaviour echoes this sentiment. A study into the impact of wearable tech on a cohort of cardiovascular patients suggested a noticeable percentage of those who were given devices to monitor their heart health experienced increased anxiety 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 pulse went up. They got more worried. They checked again, and their reading went up again.

"Upon viewing stats about ourselves that we don't really understand then, naturally, we are going to seek clarification," the psychologist says. "We check, we re-check - it becomes a self-fulfilling prophecy."