For the next few weeks, all the exercises featured here will be free. I’m trolling you, really: being skint is the best-known reason for delaying a health kick, and January is skintness’s playground. Not any more.

If there’s one thing I like less than being told what to do, it’s being told what to do in a loud voice. I believe my historic antipathy to most of fitness stems from a hatred of authority, and British Military Fitness was never, in consequence, my thing. But what if you can weaponise yourself? That’s the proposition made by Major Sam McGrath in his book Be Para Fit: The 4-week Formula For Elite Physical Fitness. I found many of his principles inherently implausible. “When you’re at your lowest ebb and everything is spent, there’s always at least 20% left in the tank”, for instance.

The programme itself, however, is hard to disprove: it is simply a fact that pushing yourself slightly harder every day will make you stronger. But first you need to find your baseline. You won’t know how superior you are to yesterday’s self just by looking in the mirror. Not for months, probably.

So you start with a functional assessment, seven exercises (you can find them all on YouTube) to test your strength. You’ll need a bar, but you can improvise with a mop, as I did, and got smelly floor water on myself. These are the overhead squat, the inline lunge, a test of shoulder mobility, a hurdle step, an active straight leg raise, a test of rotary stability and a trunk stability push-up. You also have to do a cardio baseline: 2.4km of running. How hard you found all this will determine what level of para fitness you start at. My guess is that everyone who doesn’t do this stuff all the time will end up at level one, just because it won’t be familiar.

This does not complete your first session! Far from it. But after you’ve set your baseline, the next workouts are pretty similar. You warm up with three to five minutes of running, indoor cycling, running on the spot or skipping. I’m assuming a high level of privacy – either your family is out or you have a big house.

Plainly, if you want to follow it to the letter, you will have to buy the book, so this idea isn’t free in the classic sense. But t’internet is lousy with warm-ups, cool-downs, home-circuit ideas and the rest is all running, cycling, swimming or rowing.

The question is: how do you find the motivation when there’s no camaraderie and nobody is shouting? The only place you’ll draw it from is some sense that you’re improving on your baseline. The major doesn’t recommend redoing the functional assessment, believing exercise to be its own reward. But I found that only by returning to it (at least the cardio element) after a week could I sustain any enthusiasm. And I was faster. I felt better. I slept better. I reckon the military would be ready for me now.

Fit for free

For the next five weeks, Zoe will be trying exercise that costs nothing, from online yoga to park gyms.