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A sense of nervous excitement. I can see the cold breath coming from my competitors as they do the "about to run" shuffle on the start line.

A quick movement of the hips.

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

Oh, hang on. I have to sort my tracker. So does the guy alongside me.

The person behind us sighs. I'm not moving until… there! Connection established, away I go.

Amidst the crowd, it's challenging to see a arm without a smartwatch on it. And this extends beyond us athletes who rely on them.

This is a thriving, multi-billion pound industry. Companies like Samsung Galaxy dominate, all offering an wide selection of different versions to suit a spectrum of needs. Depending on how advanced the device you select, price tags can vary between a hundred pounds to a significant investment.

"It drives me insane, I'm unable to switch off."

"It provides solace… It's like a supporter guiding me."

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

A handful of the comments people have shared from like-minded smartwatch wearers when I question what they feel about theirs.

The Data Dilemma

My feelings on mine? Currently, irritating. It's indicating I'm off pace, making me wonder whether the overhead branches I'm passing under are disrupting my satellite signal.

A vast number of us attach these compact devices onto our wrists and keep them on all day and night, apparently unconcerned with the fact they're continuously recording us.

Gone are the days when we relied on them solely to give us an idea of our daily steps. Now, they can analyse our sleep quality, blood pressure, heart rate variability (HRV), our body battery.

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

But do they do what they advertise? And are the data points we analyse a true reflection of reality? Do they boost our overall health, or do the multitude of readings and cheerleading alerts just contribute to our daily stresses?

Addiction or Aid?

"I do get a a little preoccupied with mine," one user confesses.

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

Prior to discovering she could change its configuration, her smartwatch kept telling her she was failing to be active enough. Later on, the watch keeps telling her she's had a poor sleep score.

"I am caring for a young baby, there's no point to be told my sleep was poor," she says. "That fact is all too clearly."

Is it not possible to just stop wearing it?

"I could, I suppose, but I have this push-pull dynamic with it," she says. "I appreciate it for its exercise data, but I'm unsure whether the myriad other functions it can now do is possibly overkill for me."

How Do They Work?

Every device of smartwatch has its own unique way of tracking your bodily functions and interpreting your data, but the majority use sensors on the reverse of the watch.

They typically shine small, green LED lights onto your skin which can observe capillary action, identifying your pulse rate. Sophisticated devices analyse changes in the bioimpedance that passes over the skin to gauge your recovery state.

Expert Perspectives

A data scientist says that in general for smartwatches, it's a "difficult line" - while the continuously improving tech could realistically save lives, "detecting disease before we feel unwell", it could also turn us device users into the "worried well".

He points out that some of the latest wearables can perform tests like heart rhythm analysis, which continuously monitor how stable the heart is. They can alert if someone is experiencing an irregular rhythm, where there is abnormal electrical activity in the heart causing an uneven pulse.

This does not automatically signal someone is on the verge of a cardiac event, but it can give an preliminary indication they might be more at risk of a heart problem in the long term.

But how to make sense of these numbers is not straightforward. The expert fears that as more functions are introduced, people may not be able to fully understand their data.

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

A professor specialising in wearable tech agrees. Research into the impact of wearable tech on a specific group of cardiovascular patients suggested a minority of those who were given devices to monitor their condition experienced increased anxiety and were "more inclined to use doctor's time".

She noted a cycle with her patients - they saw a alarming metric on their watch. They became worried. Their pulse increased. They got even more concerned. They checked again, and their reading went up again.

"If we see data about ourselves that we lack context for then, naturally, we are going to want to know more," the psychologist says. "We look, we obsess - it becomes a feedback loop."