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There's a nervous excitement. Apparent is the cold breath exhaled by my rivals as they do the "starting line" shuffle on the beginning point.

A swift twitch 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 adjust my device. The same goes for the person beside me.

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

Amidst the crowd, it's difficult to spot a arm without a fitness tracker on it. And it's not just us runners who use them.

It's a booming, multi-billion pound market. Companies like Apple Watch lead the market, each with an broad selection of various devices to cater to a variety of budgets. According to how high tech the model you go for, price tags can vary between £100 to a significant investment.

"It makes me crazy, it's impossible to switch off."

"It reassures me… It acts as a supporter encouraging me."

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

Just some of the responses I've received from other device users when I question what they their opinion is on theirs.

A Sea of Statistics

My feelings on mine? Currently, annoying. It's telling me my speed is wrong, causing me to question whether the overhead branches I'm passing under are disrupting my location tracking.

Countless individuals of us attach these compact gadgets onto our wrists and use them 24/7, ostensibly at ease with the fact they're continuously recording us.

Gone are the days when we used them exclusively to give us an idea of our daily steps. Now, they can track our sleep quality, stress levels, glucose levels, our VO2 max.

It's tricky to find a physical metric they don't track.

But can they do what they say they do? And are the data points we analyse a true reflection of reality? Do they boost our overall health, or do the plethora of metrics and constant notifications just increase our daily stresses?

A Complicated Bond

"I become a quite fixated with mine," one user confesses.

While she appreciates how her device monitors her runs, she finds some of its other capabilities "overwhelming" at times - a feeling first discovered during a pregnancy.

Prior to discovering she could change its configuration, her smartwatch repeatedly informed her she was not being energetic enough. In a new phase, the watch keeps telling her she's had a bad night's sleep.

"I am caring for a six-month old, I don't need to be notified I'm tired," she says. "I'm acutely aware all too clearly."

Is it not possible to just take it off?

"It's possible, I suppose, but I've got this complicated dynamic with it," she says. "I value it for its workout tracking, I just wonder whether all the other things it can now do is perhaps excessive for me."

The Technology Behind the Tracking

Different brands of smartwatch has its own proprietary way of measuring your vitals and processing your data, but the most use optical sensors on the reverse of the watch.

They usually shine tiny, coloured LED lights onto your arm which can observe blood flow, detecting your pulse rate. More advanced devices analyse changes in the electrical current that runs through the skin to gauge your nervous system activity.

A Fine Balance

One expert says that for most people for smartwatches, it's a "fine balance" - while the continuously improving tech could realistically aid early diagnosis, "spotting abnormalities before we notice anything", it could also turn us watch wearers into the "worried well".

He points out that newer wearables can conduct tests like heart rhythm analysis, which regularly monitor how stable the heart is. They can notify if someone is experiencing a heart arrhythmia, where there is irregular impulses in the heart causing an irregular heartbeat.

This does not mean someone is on the verge of a cardiac event, but it can give an early warning they might be more at risk of a heart problem in the future.

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

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

A clinical psychologist studying cardiology echoes this sentiment. Her work 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 greater stress and were "had a higher tendency to use medical services".

She noted a pattern with her patients - they saw a worrying figure on their watch. They became worried. Their pulse went up. They got even more concerned. They re-examined the data, and their heart rate rose further.

"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 obsess - it becomes a feedback loop."