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An atmosphere of building tension. Apparent is the frosty air emanating from my competitors as they perform the "starting line" jiggle on the beginning point.

A rapid movement of the hips.

I'm at my local 5km community parkrun and I'm serious. Three, two, one...

Hold on. I must sort my watch. So does the person beside me.

The person in the line expresses impatience. I won't start until… done! GPS ready, and I'm running.

During the scramble, it's hard to spot a arm without a fitness tracker on it. And it's not just us athletes who use them.

We're witnessing a booming, multi-billion dollar market. Companies like Samsung Galaxy are prevalent, each with an extensive array of various models to fit a variety of budgets. Depending on how advanced the device you select, costs can start from a hundred pounds to thousands of pounds.

"It makes me crazy, I'm unable to switch off."

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

"Please don't notify me about a bad night's sleep."

A handful of the comments people have shared from fellow device users when I inquire what they think of theirs.

A Sea of Statistics

My current opinion on my own device? Currently, irritating. It's telling me I'm not hitting my target, leading me to doubt whether the trees along my route are blocking my location tracking.

A vast number of us strap these compact devices onto our arms and use them constantly, ostensibly at ease with the fact they're perpetually monitoring us.

Gone are the days when we used them exclusively to give us an estimation of our daily steps. Currently, they can measure our nightly rest, blood pressure, oxygen saturation, our recovery score.

It's a challenge to find a physical metric they aren't designed to measure.

But can they do what they say they do? And are the numbers we obsess over a accurate representation of reality? Do they improve our daily wellness, or do the multitude of readings and motivational messages just contribute to our daily stresses?

A Love-Hate Relationship

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

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

Until she found out she could change its configuration, her smartwatch kept telling her she was failing to be productive enough. Later on, the watch keeps telling her she's had a restless night.

"I have a six-month old, I don't need to be informed I've not slept," she says. "I know that all too clearly."

Couldn't she just take it off?

"I suppose I could, perhaps, but I have this push-pull dynamic with it," she explains. "I love it for its fitness insights, I just wonder whether all the other things it can now do is possibly overkill for me."

How Do They Work?

Different brands of smartwatch has its own unique way of measuring your bodily functions and processing your data, but the vast bulk use sensors on the back of the watch.

They usually emit minute LED lights onto your skin which can monitor pulsation, recording your heartbeat. Sophisticated devices measure changes in the bioimpedance that runs through the skin to assess your recovery state.

The Professional Viewpoint

One expert says that in general for smartwatches, it's a "difficult line" - while the ever-evolving tech could realistically prevent illness, "identifying issues before we show symptoms", it could also turn us the tracked into the "worried well".

He points out that some of the latest wearables can conduct tests like electrocardiograms (ECGs), which constantly monitor how stable the heart is. They can notify if someone is experiencing an irregular rhythm, where there is abnormal 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 advance notice they might be more at risk of a heart problem in the future.

But how to understand these numbers is complex. The expert concerns that as further capabilities are incorporated, people may not be able to fully comprehend their data.

"I'm not entirely convinced that having the capacity to monitor so much data is such a positive development," he says.

A clinical psychologist specialising in wearable tech echoes this sentiment. A study into the effect of wearable tech on a specific group of cardiovascular patients suggested a significant portion of those who were given devices to monitor their cardiac function experienced greater stress and were "far more likely to use healthcare resources".

She observed a pattern with her patients - they saw a alarming metric on their watch. They grew concerned. Their heart rate increased. They got increasingly anxious. They looked a second time, and their heart rate went up again.

"If we see data about ourselves that we lack context for then, of course, we are going to seek clarification," the psychologist says. "We check, we obsess - it becomes a vicious cycle."