"Sit up straight" is useless advice, because the problem was never that you forgot to. Eight hours a day in a chair physically reshapes you. Two muscle pairs take the brunt of it, and once you know which ones, the fix is short and simple.

Two imbalances develop, and nearly every desk-related ache traces back to them.

Hips: Sitting holds your hip flexors (the muscles at the front of your hips) in a shortened position for hours until they tighten up, while your glutes, switched off from doing nothing, go weak. Tight-in-front, weak-behind tilts your pelvis and is a leading cause of lower back pain.

Upper body: Leaning toward a screen tightens your chest and lets your upper back muscles go weak and long. Your shoulders round forward and your head drifts ahead of your spine. For every inch your head juts forward, it roughly doubles the load on your neck.

The pattern is the same both times: the muscles on one side get tight, the ones on the other get weak. So you fix it the same way both times. Stretch what's tight, strengthen what's weak.

1. Kneeling hip flexor stretch (loosens the tight hips). Kneel on one knee, other foot forward in a lunge. Squeeze the glute of the down leg and push your hips forward until you feel a stretch in the front of that hip. Hold 30 seconds per side.

2. Glute bridge (wakes up the weak glutes). Lie on your back, knees bent, feet flat. Squeeze your glutes and lift your hips into a straight line from knees to shoulders. Hold 2-3 seconds, lower. Do 12-15. Drive with your glutes, not your lower back.

3. Doorway chest stretch (loosens the tight chest). Forearm on a doorframe, elbow about shoulder height, gently lean through until you feel the stretch across your chest. Hold 30 seconds per side.

4. Wall slides (strengthen the weak upper back). Stand with back flat against a wall, arms up in a goalpost, elbows and wrists touching the wall. Slide your arms overhead and back down without letting them leave the wall. Do 10. If it is hard to keep contact, that means it’s tight, and that's exactly the muscle group you're after.

5. Chin tuck (resets the forward head). Sitting or standing tall, gently draw your head straight back, making a double chin. Hold 3 seconds, repeat 10 times. This re-engages the deep neck muscles that screen time switches off.

No routine beats not holding one position for eight hours. The biggest lever isn't any single stretch, it's breaking up the sitting. Stand once an hour. Walk to refill your water. The five movements can help undo the damage, but getting up regularly stops it from accumulating in the first place.

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PS—Moving around and changing positions will help more than static posture, even if it is “good.”