Sitting for hours shortens the hip flexors, rounds the upper back, compresses the spine, and tightens the chest. If you work at a desk, your body already knows this. It sends you messages every day in the form of stiffness, aches, and that general end-of-day heaviness.
The good news is that yoga can undo most of it. Not overnight, but consistently. What matters is doing a little, often, rather than one long session once a month.
Focus on the hips, the thoracic spine, and the chest. Open what sitting closes. Strengthen what slouching weakens. That's the whole strategy.
Pose to try
Cat-Cow (Marjaryasana-Bitilasana)
On all fours, inhale and drop your belly, lift your head and tailbone (Cow). Exhale and round your spine towards the ceiling, tucking your chin and tailbone (Cat). Repeat slowly for ten breaths. Do it every morning before you open your laptop. Your back will thank you.