‘Busy weekend?’ the Friday conversation goes.

‘I’m going to Jurassic Encounter Adventure Golf at New Malden on Saturday, then, on Sunday, I’ll run…’

‘How far?’

Sharp intake of breath. ‘Forty…’

‘Miles?’

‘Yes.’

I’ve had this conversation many times over the years. Or certainly words to this effect, as this will be my first visit to Jurassic Encounter Adventure Golf, which, judging by a website that roars at me every 20 seconds or so, looks ridiculous in comparison to the notion of running 40 miles.

Mad is the typical, thoughtless adjective my listener selects. You shouldn’t have asked the question then, I think; you know I run. One such conversation led to a colleague insisting I cease running because of my ‘knees’. Every time she sees me in my shorts, I sense her inwardly tutting at my imminent knee destruction. MY KNEES ARE FINE, I want to shout; in fact, apart from a drinking accident at university, my knees have remained injury-free in close to 20 years of running.

I’m not mad.

As I write, competitors in the Grand Union Canal Race are shuffling 145 miles from Birmingham to London. One of their number, Mimi Anderson, has already run the race route in reverse to get to the start line. Should she get back to London (on foot and in one piece), she’ll have run 290 miles. The numbers are mind-boggling. There are 89 poor souls out there.

As I write, racers in the Hardmoors 110 event have been running for more than 12 hours through the night, following the Cleveland Way in Northumberland. The cut-off time limit is 36 hours and to be an ‘unsupported’ runner you must have completed a race of the ilk of the Ultra Tour du Mont Blanc, the Lakeland 100 or the West Highland Way.

As I write, 1000 athletes (an incredible number if that’s the case) are leaving Richmond as they begin the 60-mile London to Brighton Challenge. It’s not the Cleveland Way, but the North and South Downs stand between them and the sea.

As I write, there are runners in the Lake District attempting to crack the 24-hour, 42-summit, 66-mile Bob Graham Round. They started at 1am and I imagine they are somewhere high on the Helvellyn range, perhaps gliding along in the glory of a Lakeland morning, perhaps struggling and cursing their own ambition. They literally have Everest to climb.

As I write, runners will be emerging from their tents on the Hebridean island of Jura. I wish them no midges. They will look skyward at the three glorious Paps – if the weather allows – over which they will later run as part of a 16-mile loop from the island capital.

GUCR, Hardmoors 110, London to Brighton, Jura. And people say I am mad. Madness – and I don’t mean this in the genuinely mentally unhinged way – is relative, of course. There is always someone madder. One person’s madness is another person’s mundane. Step forward Mimi Anderson. Step forward the Bob Graham runner who isn’t happy with 42 peaks in 24 hours; he must claim 50 or 60. Step forward the Jura mentalists who will today seek to gallop up and down thousands of feet of loose, ankle-jarring scree in three hours. It’s not an exaggeration to say they all risk their lives in their particular pursuits. But then isn’t that a prerequisite of madness?

I sought to explain this obsessional need in Heights of Madness, my first book about cycling and walking 5000 miles between the UK’s 92 traditional county tops. I tried to explain how failing to meet arbitrary daily targets, set by myself, for no-one else and for no deadline, such as climbing a Munro, cycling 60 miles, camping, eating, reading a map, being warm, being safe, simply surviving, must be achieved or I would be reduced to a depressed wreck guzzling chocolate biscuits in my tent. I still struggle to fathom that level of obsession, despite having been the obsessive. I do not know what drives Mimi Anderson. Does she know herself? Perhaps, like me, when she woke up, she thought: My legs really hurt, but I said I was going to run to London today, so that is what I am going to do. I will stop when I get there.

Tomorrow, I will run a seventh of the distance Mimi Anderson will cover this weekend: 40 miles (or thereabouts) from Newhaven to East Grinstead, following the Vanguard Way, as I prepare for my own piece of madness in three weeks time. If this makes me mad, then several hundred ultra-runners will have to be sectioned on Monday morning.

You know who is really mad? To use a playground taunt: what you say is what you are. Those are the people who are mad. Those who haven’t felt the wind grip them on Helvellyn. Those who haven’t seen dawn rise across the North York Moors. Those who haven’t snatched a breathless view from the summit of a Jura Pap.

Those who haven’t dared to dream about where madness could take them.