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An atmosphere of nervous excitement. Apparent is the cold breath coming from my rivals as they perform the "about to run" shuffle on the start line.

A quick movement of the hips.

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

Hold on. I must adjust my tracker. As does the runner alongside me.

The person behind us expresses impatience. I refuse to go until… there! GPS ready, away I go.

Amidst the crowd, it's hard to see a arm without a fitness tracker on it. And it's not just us participants who use them.

This is a booming, massive industry. Names like Apple Watch are prevalent, all offering an broad range of diverse models to suit a range of budgets. Based on how high tech the watch you go for, price tags can range from a hundred pounds to thousands of pounds.

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

"It provides solace… It acts as a companion guiding me."

"I wish it wouldn't say I've experienced a bad night's sleep."

A handful of the comments I've had from other device users when I question what they their opinion is on theirs.

The Data Dilemma

My feelings on mine? At this moment, annoying. It's indicating I'm off pace, making me wonder whether the overhead branches along my route are disrupting my GPS connection.

A vast number of us strap these compact gadgets onto our arms and use them 24/7, seemingly unconcerned with the fact they're continuously monitoring us.

Gone are the days when we relied on them exclusively to give us an rough count of our step count. Today, they can track our nightly rest, stress levels, heart rate variability (HRV), our body battery.

It's a challenge to find a health indicator they fail to monitor.

But can they do what they advertise? And are the data points we scrutinise a faithful picture of the truth? Do they enhance our daily wellness, or do the avalanche of measurements and motivational messages just add to our daily stresses?

A Love-Hate Relationship

"I find myself getting a quite obsessed with mine," a wearer admits.

While she appreciates how her device tracks her exercise, she finds some of its other capabilities "excessive" at times - a feeling initially realised during a significant period.

Until she found out she could adjust the settings, her smartwatch kept telling her she was failing to be energetic enough. Later on, the watch insists her she's had a bad night's sleep.

"I have a infant, there's no point to be told my sleep was poor," she says. "That fact is only too well."

Couldn't she just take it off?

"I could, perhaps, but I'm in this love-hate relationship with it," she explains. "I value it for its fitness insights, I just wonder whether the additional features it can now do is maybe too much for me."

How Do They Work?

Each model of smartwatch has its own proprietary way of monitoring your health metrics and interpreting your data, but the majority use sensors on the underside of the watch.

They commonly shine tiny, coloured LED lights onto your arm which can monitor pulsation, identifying your heartbeat. Sophisticated devices analyse changes in the skin conductance that passes over the skin to get an idea of your stress levels.

Expert Perspectives

One expert says that in general for smartwatches, it's a "delicate equilibrium" - while the ever-evolving tech could potentially save lives, "spotting abnormalities before we feel unwell", it could also turn us watch wearers into the "concerned but fine".

He points out that newer wearables can carry out tests like medical-grade monitoring, which continuously monitor how normal the heart is. They can alert if someone is experiencing an irregular rhythm, where there is irregular impulses in the heart causing an arrhythmia.

This does not automatically signal someone is imminently going to suffer a cardiac event, but it can give an preliminary indication they might be more vulnerable of a heart problem in the years to come.

But how to make sense of these readings is not straightforward. The expert fears that as further capabilities are added, people may find it hard to fully comprehend their data.

"I have some doubts that being able to monitor so many things is such a beneficial thing," he says.

A clinical psychologist studying wearable tech agrees. A study into the effect of wearable tech on a set of heart condition patients suggested a significant portion of those who were given devices to monitor their heart health experienced greater stress and were "more inclined to use healthcare resources".

She observed a cycle with her patients - they noticed a concerning reading on their watch. They felt anxious. Their pulse increased. They got even more concerned. They looked a second time, and their heart rate rose further.

"When people are presented with data about ourselves that we can't properly interpret then, of course, we are going to become concerned," the psychologist says. "We look, we check again - it becomes a feedback loop."