In a life that stretches to more than 13,000 days, I can boil my existence down to five truly momentous days.

The day I got I married.

The day my first daughter was born.

The day my second daughter was born.

The day I completed the Bob Graham Round.

The day I completed Ramsay’s Round.

This is no Bill Shankley-style outburst. Hill running is certainly not a metaphorical ‘matter of life and death’. But it matters all the same. Very much.

In the past I have been reticent about what this sport means to me – an astonishing admission perhaps from someone who has spent three years writing a book devoted to the subject.

But that is the truth. When people have derided hill running as a bit ‘weird’, I have not always defended the accusation as robustly as I might. When people have asked, ‘what’s the book about?’ my declaration that ‘it’s about hill running in Scotland’ has been tinged with an air of embarrassment.

‘People think hill running is a bit weird,’ I quote Jacob Adkin, a two-time Scottish junior hill running champion, as saying in The Mountains are Calling. ‘Outside the running community, people ask, “why do you do it?” They are shocked you might spend your time running up a hill for pleasure.’

Too often, I have passively agreed with Jacob’s observation that hill runners are indeed a peculiar bunch – a close-knit dysfunctional family thriving on short shorts, sharp stones and cake.

But there is nothing weird about hill running – or at least it’s no more weird than playing the cello or going to a garden centre on a Saturday morning or sitting on a bus when you might have walked or a million other activities. From the moment I discovered this sport while racing on Snowdon some 12 years ago, watching Andi Jones descend as if his house was on fire, to the run I will do tomorrow, I do, admittedly, see madness – but it is a madness of the most beautiful kind.

I asked Jacob why he runs.

‘It’s a cliche,’ he said. ‘It’s a massive sense of freedom. Running up a hill, getting to the top, running along a ridge, seeing what you have accomplished. I have gone to places I would never have been.’

This is no cliche. Hill running is a metaphor for human existence, an act that defines who we are and what we go on to be.

I remember tears of disbelief welling as I watched the sun rise on Stob Coire Sgriodain as I entered a twelfth hour of running on Ramsay’s Round.

I remember moving over the Aonach Eagach ridge, silently, carefully, relentlessly, chasing clag-obscured shapes in the Glen Coe Skyline.

I remember plunging off Ben Nevis, kicking up dust, scree flying around my ankles, nothing mattering but the next step.

I remember seeing a full moon poised over the dark Pentlands haloed by millions of ice crystals.

I remember reaching Robinson, the final hill of a clockwise round of a Bob Graham and my mate shouting, ‘Look! Look at those hills. You own them.’

I remember climbing Scald Law, the first summit of the Carnethy 5, head-bowed against a frantic wind, then reaching a snowy, chaotic hilltop, and wondering what the hell I was doing here.

I remember crawling up the Inaccessible Pinnacle on Skye, glaringly conscious of the very thing I most take for granted: my beating heart.

I remember standing on Goatfell and being sure I could see the entire world.

All a different type of madness; all utterly beautiful. But what I remember more than anything else, that realisation that comes again and again, a recurring epiphany: how lucky we are.

The Mountains are Calling is published on Thursday 17 May. The book will be launched at Edinburgh Waterstones and can be preordered here.

This is the first post of a blog tour that runs for the next eight days. Full details below.

@MuirJonny