I spent six years sitting at a desk before my lower back started complaining. It was not dramatic, just a dull ache that showed up around 3 PM every day and got worse as the week went on. I bought a fancy chair, tried a standing desk, and still ached.

Then a physical therapist showed me one stretch, and it changed everything. It is not glamorous, but it targets exactly the muscle that desk work destroys.

The stretch: kneeling hip flexor

Here is how to do it. Kneel on the floor with one knee down and the other foot flat in front of you, like you are about to propose. Squeeze your glutes and push your hips forward until you feel a stretch in the front of the thigh on the kneeling side. Hold for thirty seconds, switch sides, repeat twice.

The reason it works: sitting all day shortens your hip flexors, the muscles at the front of your hips. Tight hip flexors pull your pelvis forward, which arches your lower back and causes exactly the ache I had. Stretch them and the pelvis settles back down.

Do it once an hour

Once a day is not enough. The magic is frequency. I do this stretch every time I get up for water, which ends up being about once an hour. Thirty seconds per side, and I am back at my desk. It takes less time than scrolling my phone.

Pair it with a standing break

The stretch works even better if you stand up every 45 minutes, even for just a minute. A quick walk to the kitchen, a few steps in place, anything that gets you out of the seated position. The body is not built for eight straight hours of sitting, and it lets you know.

Fix your screen height too

One more thing that helped me: raise the monitor so the top of the screen is at eye level. Looking down all day rounds your shoulders and makes the lower back problem worse. My laptop now sits on a stack of old books, which is the cheapest ergonomic upgrade I have ever made.

I still get a little stiff on heavy days, but the 3 PM ache is gone. Two months of the kneeling stretch and a monitor on some books did more than the fancy chair ever did. If your back hurts at a desk, start there.