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There's a feeling of anticipation. Visible is the frosty air exhaled by my rivals as they perform the "starting line" shuffle on the start line.

A rapid movement of the hips.

I'm lined up for my local Saturday morning race and I'm serious. The countdown begins...

Wait a second. I need to start my device. The same goes for the runner alongside me.

The person in the line sighs. I'm not moving until… yes! Connection established, and I'm running.

In the mele, it's difficult to see a person without a smartwatch on it. And this isn't only us participants who wear them.

We're witnessing a booming, multi-billion dollar market. Names like Apple Watch lead the market, each with an broad range of diverse models to suit a variety of budgets. Depending on how high tech the device you select, price tags can vary between £100 to a significant investment.

"I find it infuriating, I'm unable to relax."

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

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

A handful of the reactions I've received from other device users when I question what they think of theirs.

A Sea of Statistics

My thoughts on my own device? At this moment, annoying. It's indicating I'm off pace, causing me to question whether the overhead branches I'm running below are disrupting my location tracking.

Millions of us fasten these small devices onto our arms and wear them all day and night, ostensibly unconcerned with the fact they're continuously tracking us.

A distant memory are the days when we used them solely to give us an idea of our pedometer reading. Now, they can track our nightly rest, blood pressure, heart rate variability (HRV), our recovery score.

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

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 improve our mental and physical wellbeing, or do the plethora of measurements and motivational messages just contribute to our daily stresses?

A Love-Hate Relationship

"I find myself getting a a little fixated with mine," one user confesses.

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

Until she found out she could change its configuration, her smartwatch constantly alerted her she was failing to be productive enough. In a new phase, the watch insists her she's had a restless night.

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

Couldn't she just stop wearing it?

"It's possible, I suppose, but I have this love-hate relationship with it," she continues. "I love it for its fitness insights, I just wonder whether the additional features it can now do is perhaps too much for me."

The Technology Behind the Tracking

Different brands of smartwatch has its own novel way of tracking your bodily functions and analysing your data, but the majority use detectors on the reverse of the watch.

They typically project small, green LED lights onto your arm which can observe blood flow, recording your pulse rate. Sophisticated devices analyse changes in the bioimpedance that runs through the skin to get an idea of your recovery state.

A Fine Balance

A data scientist says that overall for smartwatches, it's a "delicate equilibrium" - while the rapidly advancing tech could potentially aid early diagnosis, "spotting abnormalities before we feel unwell", it could also turn us the tracked into the "anxious healthy".

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

This does not necessarily indicate someone is imminently going to suffer a heart attack, but it can give an advance notice they might be more susceptible of a heart problem in the years to come.

But how to make sense of these numbers is complicated. The expert worries that as more functions are added, people may struggle to fully comprehend their data.

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

A professor studying patient behaviour echoes this sentiment. Research into the effect of wearable tech on a set of cardiovascular patients suggested a noticeable percentage of those who were given devices to monitor their heart health experienced heightened worry and were "had a higher tendency to use medical services".

She noted a cycle with her patients - they saw a worrying figure on their watch. They felt anxious. Their heart rate rose. They got more worried. They re-examined the data, and their heart rate went up again.

"If we see stats about ourselves that we don't really understand then, naturally, we are going to seek clarification," the psychologist says. "We look, we check again - it becomes a feedback loop."