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A sense of building tension. Visible is the chilled vapour emanating from my rivals as they perform the "pre-race" shuffle on the start line.

A swift flick of the hips.

I'm participating in my local weekly parkrun event and I'm focused. Three, two, one...

Hold on. I need to sort my device. So does the person beside me.

The person in the line expresses impatience. I'm not moving until… done! GPS ready, I'm off.

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

This is a booming, multi-billion pound market. Names like Samsung Galaxy are prevalent, each with an wide selection of various versions to suit a variety of lifestyles. Based on how feature-packed the model you go for, costs can vary between an affordable sum to a significant investment.

"I find it infuriating, I can't switch off."

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

"Stop telling me I've experienced a bad night's sleep."

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

The Data Dilemma

My feelings on my own device? Right now, irritating. It's telling me my speed is wrong, causing me to question whether the foliage I'm running below are blocking my location tracking.

Millions of us strap these compact monitors onto our wrists and use them constantly, ostensibly at ease with the fact they're perpetually tracking us.

A distant memory are the days when we relied on them exclusively to give us an idea of our step count. Today, they can analyse our sleep patterns, stress levels, glucose levels, our body battery.

It's tricky to find a bodily function they fail to monitor.

But do they do what they advertise? And are the statistics we scrutinise a accurate representation of our actual health? Do they improve our mental and physical wellbeing, or do the multitude of readings and constant notifications just increase our daily stresses?

A Love-Hate Relationship

"I do get a a little obsessed with mine," a wearer reveals.

While she loves how her device records her workouts, she finds some of its other capabilities "excessive" at times - a feeling first discovered during a pregnancy.

Until she found out she could adjust the settings, her smartwatch constantly alerted her she was failing to be productive enough. Later on, the watch insists her she's had a poor sleep score.

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

Is it not possible to just stop wearing it?

"It's possible, perhaps, but I'm in this push-pull dynamic with it," she continues. "I appreciate it for its exercise data, I sometimes question whether all the other things it can now do is maybe overkill for me."

Inside the Device

Each model of smartwatch has its own unique way of tracking your health metrics and processing your data, but the majority use detectors on the back of the watch.

They typically shine small, green LED lights onto your wrist which can detect capillary action, detecting your pulse rate. Sophisticated devices detect changes in the skin conductance that flows through the skin to get an idea of your stress levels.

A Fine Balance

A data scientist says that in general for smartwatches, it's a "difficult line" - while the rapidly advancing tech could potentially prevent illness, "identifying issues before we notice anything", it could also turn us watch wearers into the "anxious healthy".

He points out that the most advanced wearables can perform tests like electrocardiograms (ECGs), which continuously monitor how healthy the heart is. They can notify if someone is experiencing a heart arrhythmia, where there is abnormal impulses in the heart causing an irregular heartbeat.

This does not necessarily indicate someone is on the verge of a heart attack, but it can give an advance notice they might be more susceptible of a stroke in the long term.

But how to interpret these figures is not straightforward. The expert worries that as more functions are introduced, people may struggle to fully understand their data.

"I'm not entirely convinced that being able to monitor so many things is such a good idea," he says.

A clinical psychologist studying wearable tech 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 greater stress and were "far more likely to use doctor's time".

She observed a vicious circle with her patients - they saw a concerning reading on their watch. They grew concerned. Their heart rate went up. They got increasingly anxious. They re-examined the data, and their anxiety went up again.

"When people are presented with numbers 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."