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There's a building tension. I can see the frosty air coming from my fellow runners as they execute the "pre-race" shuffle on the beginning point.

A quick flick of the hips.

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

Oh, hang on. I must sort my device. So does the person beside me.

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

In the mele, it's difficult to find a wrist without a fitness tracker on it. And this isn't only us runners who use them.

It's a thriving, multi-billion pound sector. Brands like Apple Watch lead the market, all offering an broad array of various versions to fit a range of budgets. According to how feature-packed the model you go for, costs can vary between £100 to thousands of pounds.

"It drives me insane, I'm unable to stop checking."

"It provides solace… It feels like a companion guiding me."

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

A handful of the responses people have shared from like-minded tracker enthusiasts when I inquire what they think of theirs.

A Sea of Statistics

My thoughts on my own device? Currently, irritating. It's indicating I'm not hitting my target, causing me to question whether the overhead branches along my route are blocking my location tracking.

Countless individuals of us attach these little gadgets onto our arms and wear them all day and night, apparently unconcerned with the fact they're constantly recording us.

Long past are the days when we used them exclusively to give us an estimation of our pedometer reading. Today, they can analyse our sleep quality, stress levels, oxygen saturation, our VO2 max.

It's a challenge to find a physical metric they don't track.

But do they do what they say they do? And are the data points we obsess over a faithful picture of our actual health? Do they boost our daily wellness, or do the multitude of readings and constant notifications just contribute to our sense of overwhelm?

A Love-Hate Relationship

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

While she values how her device records her runs, she finds some of its other functions "overwhelming" at times - a feeling first discovered during a significant period.

Before she realised she could adjust the settings, her smartwatch repeatedly informed her she was failing to be productive enough. Later on, the watch insists her she's had a bad night's sleep.

"I've got a young baby, I don't need to be informed my sleep was poor," she says. "That fact is all too clearly."

Couldn't she just take it off?

"It's possible, I suppose, but I have this push-pull dynamic with it," she explains. "I love it for its fitness insights, I just wonder whether the additional features it can now do is maybe excessive for me."

The Technology Behind the Tracking

Each model of smartwatch has its own unique way of tracking your health metrics and analysing your data, but the vast bulk use optical sensors on the underside of the watch.

They usually emit tiny, coloured LED lights onto your wrist which can observe pulsation, recording your BPM. More advanced devices analyse changes in the bioimpedance that passes over the skin to assess your nervous system activity.

A Fine Balance

One expert says that in general for smartwatches, it's a "difficult line" - while the rapidly advancing tech could potentially save lives, "detecting disease before we notice anything", it could also turn us watch wearers into the "concerned but fine".

He points out that the most advanced wearables can carry out tests like medical-grade monitoring, which continuously monitor how stable the heart is. They can notify if someone is experiencing a heart arrhythmia, where there is irregular electrical activity in the heart causing an uneven pulse.

This does not necessarily indicate someone is about to have a cardiac event, but it can give an advance notice they might be more vulnerable of a blood clot in the years to come.

But how to understand these numbers is complex. The expert concerns that as additional features are added, people may find it hard to fully contextualise their data.

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

A professor studying wearable tech concurs. Research into the influence 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 greater stress and were "had a higher tendency to use doctor's time".

She noted a pattern with her patients - they saw a alarming metric on their watch. They felt anxious. Their heart rate rose. They got increasingly anxious. They checked again, and their heart rate increased again.

"Upon viewing stats about ourselves that we don't really understand then, understandably, we are going to seek clarification," the psychologist says. "We check, we re-check - it becomes a vicious cycle."