As sure as mince pies follow turkey, January brings a battalion of resolutions and fitness drives.
Who needs a warm gym when you can get fit in the mud?
While faded gym memberships are dusted off, pledges of "early bird" swimming and yoga courses are solemnly made.
But for something more adventurous than pilates in a cosy leisure centre, how about a dose of tough military training on a January night in a dimly-lit park?
Which is why I found myself in some corner of a sodden field, being shouted at by ex-army instructors.
I had volunteered for Wales' first wave of the British Military Fitness programme, carrying out our manoeuvres on the muddy ground known to we civilians as Cardiff's Heath Park. Or rather, in true military fashion, I had been volunteered.
We were a select band of raw recruits. We may have been one short of a dirty dozen, but we were a pretty grimy eleven in double quick time.
Still smiling: Tom Bourton and organiser Huw Lewis
The hour-long session, open to everyone no matter how old, fit - or unfit - felt like a cross between rugby practice and circuit training.
With barely any light to show us the puddles, we slithered our way through sit-ups, jogs, sprints, games, races and squat thrusts, cursing the cheerful shouts of Huw, Chris and Brian as they drove us further and further into the mud.
As the medicine balls got heavier and our arms got weaker, their cries of "happy days" throughout every exercise even managed to make us laugh.
Organiser Huw Lewis, who served in the Royal Welch Fusiliers for 15 years, said the idea was to support, encourage and motivate people to get fit.
British Military Fitness was started six years ago in London by Major Robin Cope, and now has branches in Manchester, Glasgow, Edinburgh and Brighton.
"It is as close to a personal trainer as you can get," he said.
"It is the same training regime as in the army - the difference between joining a gym and this is you are buying equipment in a gym, here you are paying for expertise and experience."
And just like in real boot camps, there is not much danger of these courses being rained off. They have vowed to be at three outdoor sites across Cardiff, week in, week out, whatever the weather.
Speaking after the session, Mr Lewis said lots of effort was the only requirement needed.
"We had a cross range of ability, but everyone dug in and gelled together, and there was a good sense of humour," he said.
Richard Llewellyn, 40, from Aberdare said he would definitely be returning.
"I really enjoyed all of it, getting muddy and wet, and hopefully I will feel the benefit and lose a bit of weight," he said.
You're in the army now - or it feels like it, anyway
Fiona Robinson, 37, said the fresh air and the idea of someone bossing her around and making her exercise made her come along.
"I have been meaning to get fit before I hit the big four-oh," she added.
As for me, I will definitely be returning - I think so, at least - especially after Ryan, one of my fellow recruits, described my sit-ups as "military standard".
And he should know - he is at Cardiff's military preparation college and is using the course as part of his training as he aims to join the marines.
Sadly, those sit-ups were near the start - the less said about my feeble press-ups near the end, the better.
The Cardiff sessions are taking place at Heath Park, Pontcanna Fields and Roath Park throughout the year.