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An atmosphere of feeling of anticipation. I can see the cold breath emanating from my competitors as they perform the "about to run" jiggle on the starting line.

A rapid movement of the hips.

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

Oh, hang on. I must start my watch. So does the runner next to me.

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

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

We're witnessing a booming, multi-billion dollar sector. Companies like Apple Watch lead the market, all offering an extensive array of different versions to suit a spectrum of lifestyles. According to how feature-packed the device you go for, costs can vary between £100 to a small fortune.

"I find it infuriating, it's impossible to stop checking."

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

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

Just some of the reactions people have shared from other device users when I inquire what they feel about theirs.

The Monitoring Conundrum

My thoughts on my own device? At this moment, frustrating. It's indicating I'm off pace, causing me to question whether the foliage I'm passing under are disrupting my satellite signal.

A vast number of us attach these little gadgets onto our arms and use them all day and night, ostensibly comfortable with the fact they're perpetually recording us.

A distant memory are the days when we relied on them only to give us an estimation of our step count. Currently, they can track our sleep patterns, blood pressure, glucose levels, our VO2 max.

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

But do they do what they say they do? And are the numbers we scrutinise a faithful picture of our actual health? Do they improve our mental and physical wellbeing, or do the avalanche of measurements and cheerleading alerts just increase our daily stresses?

Addiction or Aid?

"I find myself getting a a little preoccupied with mine," one user reveals.

While she appreciates how her device monitors her runs, she finds some of its other features "excessive" at times - a feeling that became apparent during a major life event.

Before she realised she could put it into a specific mode, her smartwatch kept telling her she was failing to be active enough. Later on, the watch frequently reports her she's had a poor sleep score.

"I've got a infant, there's no point to be informed I've not slept," she says. "That fact is perfectly well."

Is it not possible to just stop wearing it?

"I could, theoretically, but I've got this complicated dynamic with it," she continues. "I love it for its fitness insights, I just wonder whether all the other things it can now do is possibly too much for me."

The Technology Behind the Tracking

Every device of smartwatch has its own novel way of measuring your vitals and processing your data, but the most use detectors on the back of the watch.

They typically emit minute LED lights onto your wrist which can detect pulsation, detecting your BPM. More advanced devices measure changes in the skin conductance that runs through the skin to gauge your stress levels.

The Professional Viewpoint

One expert says that in general for smartwatches, it's a "difficult line" - while the ever-evolving tech could actually save lives, "detecting disease before we feel unwell", it could also turn us the tracked into the "anxious healthy".

He points out that the most advanced wearables can carry out tests like medical-grade monitoring, which regularly monitor how stable the heart is. They can alert if someone is experiencing an irregular rhythm, where there is irregular signals in the heart causing an irregular heartbeat.

This does not automatically signal someone is imminently going to suffer a heart attack, 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 more functions 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 professor specialising in patient behaviour concurs. Research into the impact of wearable tech on a specific group of cardiovascular patients suggested a significant portion of those who were given devices to monitor their condition experienced increased anxiety and were "had a higher tendency to use healthcare resources".

She observed a cycle with her patients - they spotted a alarming metric on their watch. They became worried. Their BPM rose. They got even more concerned. They re-examined the data, and their reading increased again.

"Upon viewing numbers 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."