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An atmosphere of nervous excitement. I can see the chilled vapour coming from my fellow runners as they perform the "pre-race" jiggle on the starting line.

A quick flick of the hips.

I'm at my local Saturday morning race and I'm serious. It's almost time...

Wait a second. I need to sort my watch. The same goes for the guy next to me.

The person in the line sighs. I won't start until… there! Signal acquired, away I go.

During the scramble, it's difficult to find a person without a fitness tracker on it. And it's not just us athletes who use them.

It's a booming, multi-billion pound industry. Companies like Garmin lead the market, featuring an wide array of different devices to cater to a spectrum of lifestyles. According to how feature-packed the device you go for, costs can range from a hundred pounds to a significant investment.

"It makes me crazy, I can't switch off."

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

"I wish it wouldn't say about a poor sleep."

Just some of the reactions I've had from fellow smartwatch wearers when I ask what they think of theirs.

A Sea of Statistics

My thoughts on my own device? At this moment, irritating. It's telling me I'm off pace, leading me to doubt whether the foliage I'm passing under are blocking my satellite signal.

Millions of us fasten these small gadgets onto our arms and keep them on all day and night, ostensibly unconcerned with the fact they're perpetually recording us.

Gone are the days when we relied on them solely to give us an rough count of our step count. Currently, they can measure our sleep quality, heart rate, glucose levels, our recovery score.

It's tricky to find a health indicator they fail to monitor.

But can they do what they say they do? And are the numbers we scrutinise a accurate representation of reality? Do they improve our overall health, or do the multitude of metrics and constant notifications just contribute to our daily stresses?

A Love-Hate Relationship

"I find myself getting a a little preoccupied with mine," a wearer admits.

While she appreciates how her device records her exercise, she finds some of its other features "daunting" at times - a feeling initially realised during a significant period.

Before she realised she could adjust the settings, her smartwatch constantly alerted her she was failing to be productive enough. In a new phase, the watch frequently reports her she's had a restless night.

"I am caring for a infant, it's unnecessary for me to be told I'm tired," she says. "That fact is all too clearly."

Why doesn't she just remove it?

"I could, perhaps, but I have this love-hate relationship with it," she says. "I love it for its exercise data, I sometimes question whether all the other things it can now do is possibly overkill for me."

Inside the Device

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

They commonly emit small, green LED lights onto your skin which can monitor blood flow, detecting your BPM. Sophisticated devices analyse changes in the skin conductance that runs through the skin to get an idea of your stress levels.

A Fine Balance

A data scientist says that for most people for smartwatches, it's a "difficult line" - while the continuously improving tech could potentially prevent illness, "detecting disease before we show symptoms", it could also turn us watch wearers 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 healthy the heart is. They can flag if someone is experiencing atrial fibrillation (AF), where there is abnormal signals in the heart causing an arrhythmia.

This does not mean someone is about to have a cardiac event, but it can give an advance notice they might be more vulnerable of a stroke in the future.

But how to interpret these numbers is complicated. The expert fears that as further capabilities are incorporated, people may find it hard to fully contextualise their data.

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

A health researcher specialising in cardiology 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 heart health experienced heightened worry and were "far more likely to use healthcare resources".

She observed a cycle with her patients - they saw a worrying figure on their watch. They became worried. Their pulse went up. They got increasingly anxious. They re-examined the data, and their anxiety went up again.

"When people are presented with data about ourselves that we don't really understand then, naturally, we are going to seek clarification," the psychologist says. "We look, we re-check - it becomes a self-fulfilling prophecy."