The ache in your lower back by 4pm is coming from a muscle nowhere near your back.

This week's microhabit? Cheaper than the ergonomic chair, faster than the physio queue: the two-minute fix for your afternoon ache.

A tightness settles at the front of the hip, right where the thigh meets the torso, and most people who feel it assume it’s their back. It isn’t, not exactly. It’s the hip flexors, the muscle group running from the lower spine down through the pelvis to the top of the thigh (the psoas and iliacus, if you want the names), whose entire job is to lift your knee toward your chest, a movement almost nobody sitting at a desk for eight hours a day is doing often enough.

Sitting shortens them, not dramatically, not overnight, but steadily, the way anything shortens when it’s never asked to lengthen, and a shortened hip flexor pulls the front of the pelvis down and forward, tipping the lower back into a slight, permanent arch it was never built to hold all day. That’s the ache. It’s one we all know, every one of us who sits at desks and on our laptops, and it’s an ache that sits low and dull, and most people can’t actually trace its origin back to the hip, and so spend years treating it as back pain instead.

The fix doesn’t need a mat, a class or even a physio referral. Drop into a low lunge, one knee forward and bent, the other leg extended behind you with the top of that foot resting on the floor, and gently press the hips forward until you feel the stretch along the front of the back leg’s hip. Hold for a minute, then switch sides, and do it daily if you can, since the effect compounds each time you return to it. Posture tends to shift before the ache does, the pelvis no longer being dragged forward, finding it easier to sit up straight on its own.

Do it at the desk, by the bed, or while the kettle boils. It costs nothing and takes less time than making the coffee that had you sitting there in the first place, which is more than most fixes for a day spent sitting can claim.

1,000 Ways to Live Well is a Mille publication. Mille is a modern nutrition brand built around everyday rituals, starting with protein that doesn't ask you to compromise on taste. millesupergrain.com