"You are only as young as your spine is flexible and your mind is open," says Christopher Harrison, founder of AntiGravity Fitness (antigravityfitness.com). When sitting for long periods, he recommends taking a break and doing this:
Spinal Twist:Cross your right leg over your left. Reach your left elbow over your right knee. Twist your chest to the right and reach your right arm behind your chair. Look over your right shoulder and take three deep breaths. Repeat on the other side.
Hip Lube: Sit tall and take your legs as wide as you can, shifting weight onto your sit bones. Press the palms of your hands against the inside of your thighs, forcing the hips to open further. Extend your arms straight and lift your chest. Stay there for three deep breaths. Lift the toes, keep your heels on the ground, and move your knees inward and outward.