Your lower back was never built to hold one position all day. But that's exactly what a desk asks of it — hours of sitting that compress the discs in your lumbar spine, shorten the muscles around your hips, and leave the whole lower back stiff, aching, and tight by mid-afternoon. You stand up and it takes a second to straighten. You've tried sitting up straighter; it lasts ten minutes. The ache always comes back, because the cause — sitting still, for hours, every day — never goes away.
Stretching helps for an hour. A massage helps for a day. But the strain rebuilds every single time you sit back down.
