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There's a feeling of anticipation. I can see the chilled vapour emanating from my rivals as they do the "about to run" shuffle on the starting line.

A rapid movement of the hips.

I'm at my local Saturday morning race and I mean business. Three, two, one...

Oh, hang on. I have to start my device. The same goes for the person alongside me.

The person in the line expresses impatience. I'm not moving until… yes! Signal acquired, and I'm running.

Amidst the crowd, it's hard to spot a person without a fitness tracker on it. And it's not just us runners who rely on them.

It's a thriving, multi-billion dollar market. Names like Apple Watch lead the market, all offering an extensive selection of various devices to suit a spectrum of budgets. According to how advanced the device you select, costs can start from £100 to a small fortune.

"I find it infuriating, I'm unable to switch off."

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

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

A handful of the responses I've had from like-minded tracker enthusiasts when I ask what they feel about theirs.

The Data Dilemma

My current opinion on mine? At this moment, frustrating. It's telling me I'm not hitting my target, causing me to question whether the overhead branches along my route are disrupting my GPS connection.

Millions of us fasten these little devices onto our wrists and wear them all day and night, apparently comfortable with the fact they're continuously recording us.

Gone are the days when we depended on them solely to give us an idea of our daily steps. Currently, they can measure our sleep quality, heart rate, glucose levels, our VO2 max.

It's a challenge to find a physical metric they don't track.

But can they do what they say they do? And are the data points we obsess over a faithful picture of our actual health? Do they boost our overall health, or do the plethora of measurements and motivational messages just increase our sense of overwhelm?

Addiction or Aid?

"I find myself getting a bit obsessed with mine," an individual confesses.

While she values how her device tracks her runs, she finds some of its other functions "overwhelming" at times - a feeling initially realised during a major life event.

Until she found out she could put it into a specific mode, her smartwatch repeatedly informed her she was being insufficiently productive enough. Later on, the watch insists her she's had a restless night.

"I am caring for a young baby, there's no point to be notified my sleep was poor," she says. "I'm acutely aware only too well."

Couldn't she just stop wearing it?

"I could, theoretically, but I'm in this love-hate relationship with it," she continues. "I value it for its fitness insights, I sometimes question whether the additional features it can now do is maybe overkill for me."

Inside the Device

Different brands of smartwatch has its own unique way of measuring your bodily functions and analysing your data, but the vast bulk use sensors on the reverse of the watch.

They commonly shine minute LED lights onto your wrist which can monitor pulsation, identifying your BPM. More advanced devices detect changes in the skin conductance that passes over the skin to assess your nervous system activity.

The Professional Viewpoint

A professor says that overall for smartwatches, it's a "fine balance" - while the ever-evolving tech could potentially save lives, "identifying issues before we feel unwell", it could also turn us watch wearers into the "anxious healthy".

He points out that newer wearables can carry out tests like heart rhythm analysis, which constantly monitor how healthy the heart is. They can alert if someone is experiencing an irregular rhythm, where there is abnormal signals in the heart causing an uneven pulse.

This does not necessarily indicate someone is about to have a heart attack, but it can give an early warning they might be more vulnerable of a heart problem in the years to come.

But how to understand these figures is complicated. The expert fears that as additional features are added, people may not be able to fully contextualise their data.

"I remain sceptical that having the capacity to monitor so much data is such a beneficial thing," he says.

A professor studying cardiology agrees. Her work into the influence of wearable tech on a specific group of heart condition patients suggested a minority of those who were given devices to monitor their condition experienced greater stress and were "far more likely to use medical services".

She identified a vicious circle with her patients - they noticed a concerning reading on their watch. They felt anxious. Their BPM rose. They got increasingly anxious. They checked again, and their anxiety rose further.

"Upon viewing numbers about ourselves that we lack context for then, naturally, we are going to become concerned," the psychologist says. "We look, we check again - it becomes a vicious cycle."