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There's a building tension. I can see the cold breath coming from my competitors as they do the "starting line" shuffle on the start line.

A swift twitch of the hips.

I'm at my local weekly parkrun event and I'm focused. It's almost time...

Oh, hang on. I have to start my watch. So does the runner alongside me.

The person behind us expresses impatience. I refuse to go until… yes! GPS ready, I'm off.

During the scramble, it's hard to find a arm without a smartwatch on it. And this extends beyond us runners who rely on them.

This is a booming, multi-billion dollar sector. Brands like Garmin are prevalent, all offering an wide range of various versions to fit a variety of needs. According to how high tech the watch you go for, price tags can vary between a hundred pounds to thousands of pounds.

"It makes me crazy, it's impossible to stop checking."

"It comforts me… It's like a supporter encouraging me."

"Please don't notify me I've experienced a poor sleep."

A small sample of the reactions I've received from other tracker enthusiasts when I ask what they their opinion is on theirs.

The Monitoring Conundrum

My current opinion on mine? At this moment, annoying. It's reporting my speed is wrong, leading me to doubt whether the overhead branches I'm running below are interfering with my satellite signal.

A vast number of us strap these small monitors onto our wrists and use them constantly, ostensibly comfortable with the fact they're perpetually tracking us.

Long past are the days when we depended on them exclusively to give us an estimation of our step count. Today, they can track our sleep quality, blood pressure, heart rate variability (HRV), our VO2 max.

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

But do they do what they claim to do? And are the numbers we scrutinise a true reflection of reality? Do they boost our daily wellness, or do the multitude of readings and cheerleading alerts just add to our everyday anxiety?

Addiction or Aid?

"I do get a bit preoccupied with mine," a wearer confesses.

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

Prior to discovering she could put it into a specific mode, her smartwatch kept telling her she was not being productive enough. Later on, the watch frequently reports her she's had a restless night.

"I've got a young baby, there's no point to be informed my sleep was poor," she says. "I know that only too well."

Why doesn't she just remove it?

"I suppose I could, I suppose, but I have this push-pull dynamic with it," she explains. "I appreciate it for its workout tracking, I sometimes question whether all the other things it can now do is maybe too much for me."

How Do They Work?

Every device of smartwatch has its own novel way of monitoring your health metrics and analysing your data, but the vast bulk use optical sensors on the reverse of the watch.

They typically emit minute LED lights onto your arm which can detect capillary action, detecting your pulse rate. Sophisticated devices detect changes in the bioimpedance that runs through the skin to assess your stress levels.

Expert Perspectives

A data scientist says that overall for smartwatches, it's a "delicate equilibrium" - while the continuously improving tech could potentially save lives, "spotting abnormalities before we feel unwell", it could also turn us device users into the "anxious healthy".

He points out that newer wearables can conduct tests like medical-grade monitoring, which continuously monitor how healthy the heart is. They can notify if someone is experiencing an irregular rhythm, where there is irregular impulses in the heart causing an uneven pulse.

This does not mean someone is imminently going to suffer a cardiac event, but it can give an preliminary indication they might be more at risk of a stroke in the years to come.

But how to interpret these numbers is complicated. The expert worries that as additional features are introduced, people may struggle to fully understand their data.

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

A professor studying wearable tech echoes this sentiment. Her work into the impact of wearable tech on a specific group of heart condition patients suggested a minority of those who were given devices to monitor their cardiac function experienced increased anxiety and were "more inclined to use doctor's time".

She observed a vicious circle with her patients - they saw a worrying figure on their watch. They felt anxious. Their heart rate increased. They got more worried. They looked a second time, and their reading increased again.

"If we see stats about ourselves that we can't properly interpret then, understandably, we are going to seek clarification," the psychologist says. "We monitor, we check again - it becomes a feedback loop."