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A sense of nervous excitement. Visible is the chilled vapour emanating from my fellow runners as they execute the "pre-race" jiggle on the starting line.

A quick twitch of the hips.

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

Oh, hang on. I have to start my watch. As does the guy alongside me.

The person behind us sighs. I'm not moving until… yes! Signal acquired, I'm off.

Amidst the crowd, it's difficult to see a wrist without a fitness tracker on it. And this extends beyond us runners who rely on them.

This is a thriving, multi-billion pound sector. Brands like Samsung Galaxy are prevalent, featuring an broad array of different models to cater to a range of budgets. Depending on how advanced the model you choose, costs can start from a hundred pounds to a small fortune.

"It drives me insane, it's impossible to stop checking."

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

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

A small sample of the comments people have shared from like-minded tracker enthusiasts when I ask what they their opinion is on theirs.

The Data Dilemma

My thoughts on mine? At this moment, annoying. It's telling me I'm off pace, making me wonder whether the trees along my route are interfering with my satellite signal.

Millions of us attach these little gadgets onto our wrists and wear them constantly, seemingly unconcerned with the fact they're continuously recording us.

Long past are the days when we used them solely to give us an rough count of our pedometer reading. Now, they can analyse our nightly rest, heart rate, heart rate variability (HRV), our recovery score.

It's difficult to find a physical metric they aren't designed to measure.

But are they able to do what they say they do? And are the data points we obsess over a faithful picture of the truth? Do they improve our daily wellness, or do the avalanche of metrics and cheerleading alerts just add to our everyday anxiety?

A Love-Hate Relationship

"I do get a quite fixated with mine," a wearer confesses.

While she appreciates how her device tracks her exercise, she finds some of its other features "excessive" at times - a feeling that became apparent during a major life event.

Until she found out she could change its configuration, her smartwatch kept telling her she was being insufficiently active enough. Now, the watch insists her she's had a restless night.

"I have a infant, I don't need to be told my sleep was poor," she says. "I know that only too well."

Is it not possible to just take it off?

"I could, perhaps, but I've got this love-hate relationship with it," she continues. "I value it for its exercise data, 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 novel way of measuring your vitals and analysing your data, but the majority use sensors on the reverse of the watch.

They usually shine tiny, coloured LED lights onto your arm which can detect pulsation, detecting your pulse rate. Sophisticated devices analyse changes in the skin conductance that runs through the skin to get an idea of your nervous system activity.

Expert Perspectives

A professor says that in general for smartwatches, it's a "delicate equilibrium" - while the rapidly advancing tech could realistically aid early diagnosis, "identifying issues before we notice anything", it could also turn us device users into the "concerned but fine".

He points out that the most advanced wearables can perform tests like medical-grade monitoring, which continuously monitor how normal the heart is. They can alert if someone is experiencing atrial fibrillation (AF), where there is irregular signals in the heart causing an arrhythmia.

This does not necessarily indicate someone is on the verge of a cardiac event, but it can give an early warning they might be more susceptible of a blood clot in the long term.

But how to make sense of these readings is complicated. The expert fears that as further capabilities are added, people may not be able to fully understand their data.

"I'm not entirely convinced that being able to monitor so much data is such a beneficial thing," he says.

A health researcher focusing on patient behaviour concurs. A study into the impact of wearable tech on a cohort of individuals with health issues suggested a noticeable percentage of those who were given devices to monitor their heart health experienced increased anxiety and were "had a higher tendency to use doctor's time".

She identified a pattern with her patients - they spotted a concerning reading on their watch. They grew concerned. Their heart rate increased. They got even more concerned. They re-examined the data, and their reading went up again.

"When people are presented with numbers about ourselves that we don't really understand then, naturally, we are going to want to know more," the psychologist says. "We look, we obsess - it becomes a feedback loop."