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

A quick flick of the hips.

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

Hold on. I need to start my device. As does the person beside me.

The person in the line tuts. I won't start until… there! GPS ready, I'm off.

Amidst the crowd, it's challenging to find a wrist without a fitness tracker on it. And this extends beyond us athletes who wear them.

This is a explosive, multi-billion pound market. Brands like Apple Watch are prevalent, featuring an extensive range of diverse versions to cater to a range of budgets. Depending on how advanced the model you go for, prices can range from an affordable sum to a significant investment.

"It drives me insane, I can't switch off."

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

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

Just some of the comments I've had from fellow device users when I inquire what they feel about theirs.

The Monitoring Conundrum

My feelings on mine? Currently, annoying. It's reporting I'm off pace, leading me to doubt whether the overhead branches along my route are interfering with my satellite signal.

Millions of us attach these compact monitors onto our wrists and wear them 24/7, ostensibly comfortable with the fact they're perpetually recording us.

Gone are the days when we relied on them solely to give us an estimation of our daily steps. Currently, they can measure our nightly rest, stress levels, oxygen saturation, our VO2 max.

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

But are they able to do what they say they do? And are the numbers we obsess over a true reflection of the truth? Do they enhance our daily wellness, or do the plethora of metrics and cheerleading alerts just contribute to our daily stresses?

Addiction or Aid?

"I find myself getting a a little fixated with mine," a wearer confesses.

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

Until she found out she could adjust the settings, her smartwatch constantly alerted her she was being insufficiently productive enough. In a new phase, the watch keeps telling her she's had a bad night's sleep.

"I have a infant, there's no point to be told I've not slept," she says. "That fact is all too clearly."

Why doesn't she just take it off?

"I could, perhaps, but I've got this love-hate relationship with it," she explains. "I love it for its workout tracking, I sometimes question whether all the other things it can now do is maybe overkill for me."

How Do They Work?

Different brands of smartwatch has its own unique way of measuring your health metrics and analysing your data, but the majority use detectors on the back of the watch.

They commonly project tiny, coloured LED lights onto your skin which can observe blood flow, detecting your pulse rate. Sophisticated devices measure changes in the skin conductance that passes over the skin to assess your stress levels.

A Fine Balance

One expert says that in general for smartwatches, it's a "fine balance" - while the rapidly advancing tech could realistically prevent illness, "spotting abnormalities before we notice anything", it could also turn us the tracked into the "concerned but fine".

He points out that the most advanced wearables can conduct tests like medical-grade monitoring, which continuously monitor how stable the heart is. They can alert if someone is experiencing atrial fibrillation (AF), where there is abnormal electrical activity in the heart causing an irregular heartbeat.

This does not mean someone is about to have a heart attack, but it can give an early warning they might be more susceptible of a stroke in the future.

But how to interpret these figures is complicated. The expert worries that as additional features are added, people may find it hard to fully contextualise their data.

"I'm not entirely convinced that being able to monitor so many metrics is such a beneficial thing," he says.

A professor studying patient behaviour echoes this sentiment. Her work into the influence of wearable tech on a cohort of individuals with health issues suggested a significant portion of those who were given devices to monitor their cardiac function experienced greater stress and were "had a higher tendency to use healthcare resources".

She noted a vicious circle with her patients - they noticed a worrying figure on their watch. They grew concerned. Their pulse went up. They got even more concerned. They re-examined the data, and their reading went up again.

"Upon viewing stats about ourselves that we lack context for then, naturally, we are going to seek clarification," the psychologist says. "We check, we check again - it becomes a vicious cycle."