Just as Old Testament prophets rarely said, “You know what, I’m not sure that voice I heard was God’s, after all,” so columnists rarely admit to be being wrong. As soon as the pundit’s air of infallibility vanishes, the project collapses as fast as stage scenery when the curtain goes down.

But the Nick Cohen Health and Beauty Workout ™ is nothing if not bitingly honest. On the assurance of the editor that he will collect and burn every copy of this magazine, I am prepared to say I may be wrong about gyms. Not wholly wrong. Indeed, my wrongness, if it exists, which you are entitled to doubt, is so infinitesimally small you may need an electron microscope to see it. Still, the possibility must be faced, so here goes.

When you run, walk or cycle you connect to the environment. You see the town you may have lived in for decades afresh. You feel the changing of the seasons and check the forecasts with the interest of someone who has learned weather isn’t just something that happens in the time it takes to walk to the garage. You become a part of nature: not the awesome nature of Alps and deserts, but your quasi-natural world of municipal parks and canal paths, cut-throughs and residential side streets.

Gyms, by contrast, are as unnatural as Liberal Democrat landslides. The windows don’t open. The light is artificial. The owners pump perfume into the air to disguise the body odour. Music blares as everyone except the perfectly-toned succumbs to the body dysmorphia that the sight of svelte men and women lifting and rowing provokes. The cost is outrageous, by the way. Virgin, to pick a gym membership at random, charges £1,140 a year. You could buy an excellent road bike for that or 10 pairs of decent running shoes. Gym membership makes no sense unless you go most days. And who wants to waste their lives in a sterile sweatpit for narcissistic inadequates? A prison whose inmates have given themselves a life sentence on a treadmill without parole or hope of appeal?

At this point, the columnist bellows “No one!” and hits the send button. But this columnist could be wrong. The NHS fitness guidelines recommend 150 minutes of “moderate-intensity” exercise a week: by moderate, their doctors mean brisk walking or cycling, and as I said in the last issue, if you add 30 to 60 minutes of that a day to your routine you will see the weight fall off you. It is all the millions of obese and overweight in this country need to do, as long as they watch their diets as well.

Alternatively, the NHS suggests 75 minutes of vigorous activity, which for the purposes of this column will mean running. To do moderate or vigorous exercise you need to strength-train too. When I began my transformation to the godlike figure you see beaming like Apollo atop Olympus, all I did was walk. I still developed a shooting pain on the outside of my right knee. The mere act of strolling around had inflamed my iliotibial band.

There was nothing wrong with my knees. A lifetime of sitting in newspaper offices, pubs and kitchens had weakened my hip and glute (butt) muscles and my legs were overcompensating. The pain went when I started to improve my body strength. Now that I run, I injure myself more than I should because I don’t dedicate enough time to weights.

It’s not just the sedentary life that does for you. At some point in your thirties, your body stops building muscle and starts to eat it up. Unless you build strength you will struggle eventually to stretch for a box on a high shelf or open a tight jamjar or cope without strain with a thousand and one everyday tasks.

Joining a gym and paying a personal trainer to give you a modest workout programme is not quite as terrible an idea as I make it out to be. You don’t have to. There are free strength workouts for beginners on the Fitness Blender and NHS sites, and free beginners courses on the Yoga With Adriene YouTube channel (she’s lovely, incidentally: you want to keep going because you can’t bear the thought of disappointing her).

Alongside a strength routine — no weights or kettlebells, just simple squats and lunges — download one of the dozens of “from couch to 5k” apps on your phone and plug in the headphones. The first week will have you running in one-minute bursts. They will hurt, and you will think you cannot move another step. But after two months you will be able to run for half an hour. After six, you will be able to compete in a 10-kilometre race. Trust me, you will. For I am a columnist and am never wrong.