As I approach the gleaming towers of Canary Wharf, I’m filled with an overwhelming sense of dread.

At 23 years of age, and with what must rank among the least imposing physiques in the history of mankind, I’m about to embark on my first military-style boot camp, ‘Regiment Reebok.’

My reservations are enormous: I’m ludicrously unfit, and have never had the slightest inclination to put myself through gruelling drills under duress from anyone, let alone a former Marine.

Nonetheless, here I am, signing a disclaimer absolving anyone else of guilt in the event that I - as I suspect is likely - do myself a serious physical injury or die.

Our task-master, former Royal Marine Commando Chris Geran, begins the session with a gentle jog around our designated patch of greenery in Canary Wharf. “This isn’t so bad”, I think to myself. “Maybe these camps aren’t as hard as people make out.”

Chris addresses us: “Keep running on the spot, all the time. If I see anyone stopping, we’ll both be doing press-ups. I love doing ‘em... I’ll manage two, three hundred easily.”

I pump my scrawny legs for all they’re worth, silmultaneously baffled at the notion of anyone enjoying press-ups, and fearing the inevitable repurcussions of non-compliance. I remind myself that my companions, most of whom are thirty-something office workers from the banks and law firms of the Wharf, are doing this of their own free volition.

We are split into teams of eight for the rest of the session, taking turns to visit a four different stations, where trainers launch into drills with alarming relish.

Before long, my arms and legs begin to shake, and I feel sick. We continue, occasionally exchanging knowing grimaces with one another, and huffing and blowing as we pass weights between us in between sprints and burpees.

After what seems an eternity, we finish the final stage and embark on a seemingly endless warm-down of stretches, press-ups and a variety of ‘planks’, which involve holding the press-up position for prolonged periods of time. In normal circumstances this would be manageable, but after the hour we’ve all just been put through, it feels closer to a medieval torture regime than a gente stretch.

Upon finally finishing, the relief is overwhelming. Confusingly, at least for me, it is also accompanied by a feeling of satisfaction, and the bizarre realisation that I have found the experience, dare I say, quite rewarding.

Afterwards, Chris, my tormenter-in-chief explains amicably that he works hard to make his camps accessible for everyone. “Fitness should be fun,” he says. “Nobody wants to be punished - the workout itself is hard enough. You can shout at some people because they enjoy it, but others are struggling enough already.”

As I waddle home I find myself pondering whether to return to next week’s session - something I’m not sure whether to attribute to my slightly disorientated state or the brilliant sense of self-satisfaction I felt at managing to get through it. I’m aching, shattered and smug.