I am on a treadmill, next to trainer and gympreneur Alexei (Lex) Sharp, opposite a mirror, thinking about how selves are inherently disgusting. I don’t have a problem esteeming mine; I just don’t want to look at it. I am walking at a mild incline with a mask over my mouth, tubes sprouting off me, like a Doctor Who monster with emphysema. I’m not naked, at least. This is my MOT part two: what’s going on between the outside and the inside; my muscle density, heart, lungs. So, you know, worse than naked.

I’m having a VO 2 (oxygen volume) test, which measures heart and lung efficiency by harrying my muscles into activity and then seeing how much oxygen reaches them. It’s nothing drastic, just walking ever more steeply for 14 minutes, but exercise makes me cantankerous.

My VO 2 score, at 33.8, is declared “good”. Look, I know more about statistics than I do about lungs: if 26.5 is very poor and 41 is excellent, there’s a tolerance band from “incredibly rubbish, nearly dead” to “amazingly fit, probably unbearable” that I’m almost in the middle of. The word for that is not “good”; it’s “fractionally above average, adjusting for age and weight” (a lady athlete, for comparison, would be 70).

Lex says that only interval training – short bouts close to your maximum, alternated with medium intensity – can improve things. To get good you have to be out of breath, and regularly. The only way to get breathlessness into your life is to distract yourself (that’s why most spin studios look like a nightclub) or to hate yourself.

Next, my muscle strength is tested on these stupidly impressive German e-gym machines, each costing as much as a car. Instructions emanate from a screen, then encourage you with 80s video-game graphics. I am pushing 200 kilograms using my thighs, but all my mind is focused on is getting the dot to stay within the wiggly lines.

My maximum strength analysis is as follows: leg press, 183kg; chest press, 41kg; lat pull-down 45kg. This information will make me hard to like: it says my biological age is 21. My response is that fitness is a racket; the most I’ve exerted my arms in a decade is pushing down the AeroPress.

Nevertheless, humans are target-driven. Now I’m 21, I want to be 18. Sadly, lifting things is tedious – that’s why we had the industrial revolution – so the prescription is the same: distraction or masochism. I’ll try distraction first, then use shortcuts as they arise – though I’m guessing that they won’t.