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There's a feeling of anticipation. Visible is the cold breath exhaled by my fellow runners as they do the "pre-race" wiggle on the starting line.

A quick twitch of the hips.

I'm at my local 5km community parkrun and I mean business. The countdown begins...

Hold on. I need to sort my device. As does the guy beside me.

The person behind us sighs. I'm not moving until… yes! GPS ready, I'm off.

During the scramble, it's difficult to see a person without a fitness tracker on it. And this extends beyond us athletes who rely on them.

This is a booming, massive sector. Companies like Garmin are prevalent, featuring an broad range of diverse models to fit a spectrum of budgets. Based on how feature-packed the device you go for, costs can range from a hundred pounds to thousands of pounds.

"It drives me insane, I can't relax."

"It reassures me… It acts as a friend guiding me."

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

Just some of the responses I've received from like-minded tracker enthusiasts when I inquire what they their opinion is on theirs.

The Data Dilemma

My thoughts on mine? Currently, frustrating. It's reporting I'm not hitting my target, causing me to question whether the foliage I'm passing under are blocking my satellite signal.

Countless individuals of us strap these small gadgets onto our wrists and use them all day and night, apparently comfortable with the fact they're continuously recording us.

Long past are the days when we relied on them only to give us an idea of our step count. Today, they can measure our sleep patterns, heart rate, oxygen saturation, our body battery.

It's a challenge to find a physical metric they fail to monitor.

But are they able to do what they claim to do? And are the numbers we scrutinise a true reflection of reality? Do they improve our mental and physical wellbeing, or do the avalanche of metrics and motivational messages just increase our daily stresses?

Addiction or Aid?

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

While she loves how her device tracks her workouts, she finds some of its other functions "overwhelming" at times - a feeling that became apparent during a major life event.

Before she realised she could change its configuration, her smartwatch kept telling her she was failing to be energetic enough. In a new phase, the watch insists her she's had a bad night's sleep.

"I am caring for a six-month old, I don't need to be notified I'm tired," she says. "I know that only too well."

Couldn't she just remove it?

"I suppose I could, I suppose, but I'm in this push-pull dynamic with it," she explains. "I love it for its exercise data, I just wonder whether the additional features it can now do is maybe excessive for me."

How Do They Work?

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

They usually shine small, green LED lights onto your arm which can monitor capillary action, identifying your BPM. More advanced devices analyse changes in the bioimpedance that passes over the skin to gauge your stress levels.

The Professional Viewpoint

One expert says that in general for smartwatches, it's a "delicate equilibrium" - while the continuously improving tech could actually prevent illness, "detecting disease before we notice anything", it could also turn us watch wearers into the "worried well".

He points out that newer wearables can carry out tests like electrocardiograms (ECGs), which continuously monitor how normal the heart is. They can notify if someone is experiencing atrial fibrillation (AF), where there is abnormal electrical activity in the heart causing an arrhythmia.

This does not necessarily indicate someone is about to have a heart attack, but it can give an advance notice they might be more at risk of a stroke in the long term.

But how to interpret these readings is complex. The expert fears that as more functions are introduced, people may not be able to fully understand their data.

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

A professor specialising in cardiology agrees. Research into the influence of wearable tech on a set of individuals with health issues suggested a noticeable percentage of those who were given devices to monitor their condition experienced greater stress and were "far more likely to use doctor's time".

She identified a pattern with her patients - they spotted a alarming metric on their watch. They grew concerned. Their pulse went up. They got more worried. They checked again, and their reading went up again.

"When people are presented with data about ourselves that we don't really understand then, of course, we are going to become concerned," the psychologist says. "We monitor, we re-check - it becomes a vicious cycle."