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An atmosphere of feeling of anticipation. Visible is the cold breath exhaled by my fellow runners as they do the "starting line" jiggle on the starting line.

A quick movement of the hips.

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

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

The person behind us tuts. I won't start until… there! Connection established, away I go.

In the mele, it's hard to spot a wrist without a fitness tracker on it. And this extends beyond us runners who wear them.

We're witnessing a explosive, multi-billion pound market. Companies like Apple Watch dominate, each with an wide array of various models to fit a range of needs. Depending on how high tech the model you go for, prices can range from a hundred pounds to a small fortune.

"It makes me crazy, it's impossible to switch off."

"It comforts me… It's like a companion guiding me."

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

A small sample of the responses people have shared from like-minded device users when I question what they feel about theirs.

The Data Dilemma

My thoughts on my own device? Currently, frustrating. It's telling me I'm not hitting my target, making me wonder whether the foliage I'm running below are disrupting my satellite signal.

Countless individuals of us strap these little devices onto our wrists and keep them on constantly, apparently comfortable with the fact they're perpetually monitoring us.

A distant memory are the days when we used them exclusively to give us an idea of our step count. Currently, they can measure our nightly rest, heart rate, heart rate variability (HRV), our body battery.

It's tricky to find a health indicator they aren't designed to measure.

But can they do what they claim to do? And are the numbers we obsess over a accurate representation of our actual health? Do they boost our overall health, or do the plethora of measurements and cheerleading alerts just increase our everyday anxiety?

A Love-Hate Relationship

"I become a quite obsessed with mine," one user confesses.

While she appreciates how her device monitors her workouts, she finds some of its other capabilities "daunting" at times - a feeling first discovered during a significant period.

Prior to discovering she could put it into a specific mode, her smartwatch constantly alerted her she was not being active enough. Later on, the watch frequently reports her she's had a restless night.

"I have a six-month old, it's unnecessary for me to be notified my sleep was poor," she says. "I know that perfectly well."

Is it not possible to just stop wearing it?

"It's possible, perhaps, but I have this push-pull dynamic with it," she says. "I love it for its fitness insights, but I'm unsure whether the additional features it can now do is possibly excessive for me."

The Technology Behind the Tracking

Every device of smartwatch has its own novel way of measuring your health metrics and processing your data, but the most use sensors on the back of the watch.

They usually project minute LED lights onto your wrist which can detect blood flow, identifying your pulse rate. More advanced devices measure changes in the bioimpedance that passes over the skin to get an idea of your nervous system activity.

A Fine Balance

A data scientist says that overall for smartwatches, it's a "difficult line" - while the ever-evolving tech could actually prevent illness, "detecting disease before we feel unwell", it could also turn us device users into the "anxious healthy".

He points out that the most advanced wearables can carry out tests like heart rhythm analysis, which constantly monitor how stable the heart is. They can alert if someone is experiencing a heart arrhythmia, where there is irregular signals in the heart causing an irregular heartbeat.

This does not automatically signal 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 complicated. 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 much data is such a positive development," he says.

A professor studying patient behaviour agrees. Her work into the effect of wearable tech on a specific group of heart condition patients suggested a significant portion of those who were given devices to monitor their condition experienced increased anxiety and were "far more likely to use healthcare resources".

She observed a cycle with her patients - they saw a concerning reading on their watch. They grew concerned. Their pulse rose. They got more worried. They re-examined the data, and their heart rate increased again.

"Upon viewing numbers about ourselves that we lack context for then, naturally, we are going to seek clarification," the psychologist says. "We check, we re-check - it becomes a self-fulfilling prophecy."