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There's a nervous excitement. Apparent is the cold breath exhaled by my fellow runners as they perform the "about to run" shuffle on the starting line.

A quick twitch of the hips.

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

Hold on. I must adjust my watch. As does the person alongside me.

The person waiting tuts. I'm not moving until… yes! GPS ready, I'm off.

Amidst the crowd, it's hard to see a wrist without a wearable on it. And it's not just us runners who rely on them.

This is a thriving, multi-billion dollar market. Brands like Apple Watch lead the market, each with an wide array of various devices to cater to a range of budgets. According to how advanced the watch you select, costs can vary between a hundred pounds to thousands of pounds.

"I find it infuriating, it's impossible to relax."

"It reassures me… It feels like a companion supporting me."

"I wish it wouldn't say I've experienced a poor sleep."

A handful of the comments I've had from fellow tracker enthusiasts when I question what they feel about theirs.

A Sea of Statistics

My current opinion on my own device? Currently, frustrating. It's indicating I'm off pace, making me wonder whether the trees along my route are blocking my GPS connection.

Countless individuals of us fasten these compact devices onto our wrists and use them 24/7, seemingly comfortable with the fact they're constantly tracking us.

Gone are the days when we used them exclusively to give us an rough count of our daily steps. Now, they can measure our sleep patterns, heart rate, oxygen saturation, our VO2 max.

It's difficult to find a bodily function they aren't designed to measure.

But can they do what they say they do? And are the data points we obsess over a accurate representation of the truth? Do they enhance our mental and physical wellbeing, or do the multitude of readings and constant notifications just contribute to our daily stresses?

A Complicated Bond

"I become a bit preoccupied with mine," a wearer admits.

While she loves how her device monitors her runs, she finds some of its other features "overwhelming" at times - a feeling that became apparent during a pregnancy.

Until she found out she could adjust the settings, her smartwatch kept telling her she was being insufficiently energetic enough. Now, the watch keeps telling her she's had a restless night.

"I've got a six-month old, I don't need to be informed I'm tired," she says. "I'm acutely aware all too clearly."

Is it not possible to just remove it?

"I suppose I could, I suppose, but I've got this complicated dynamic with it," she explains. "I appreciate it for its fitness insights, I sometimes question whether the additional features it can now do is perhaps excessive for me."

How Do They Work?

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

They typically project minute LED lights onto your arm which can observe pulsation, detecting your pulse rate. Higher-end devices analyse changes in the bioimpedance that passes over the skin to get an idea of your nervous system activity.

Expert Perspectives

A professor says that for most people for smartwatches, it's a "delicate equilibrium" - while the continuously improving tech could potentially save lives, "spotting abnormalities before we show symptoms", it could also turn us watch wearers into the "concerned but fine".

He points out that newer wearables can carry out tests like heart rhythm analysis, which continuously monitor how normal the heart is. They can notify if someone is experiencing a heart arrhythmia, where there is abnormal 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 early warning they might be more at risk of a heart problem in the years to come.

But how to interpret these numbers is not straightforward. The expert concerns that as further capabilities are incorporated, people may not be able to fully comprehend their data.

"I have some doubts that the ability to monitor so many things is such a good idea," he says.

A clinical psychologist focusing on cardiology concurs. Her work into the effect of wearable tech on a cohort of cardiovascular patients suggested a significant portion of those who were given devices to monitor their condition experienced increased anxiety and were "more inclined to use healthcare resources".

She identified a pattern with her patients - they saw a worrying figure on their watch. They felt anxious. Their pulse increased. They got more worried. They checked again, and their anxiety went up again.

"When people are presented with data about ourselves that we can't properly interpret then, understandably, we are going to want to know more," the psychologist says. "We monitor, we check again - it becomes a feedback loop."