The muscles that probably need the most stretching are those in the lower part of the body. Stress on the spine is greater when you are sitting than when you are standing. Muscles automatically exert hundred of pounds of force when you are standing up- but even more when you are sitting down. And much of the force is directed right at the spine, especially if you have the common habit of leaning forward while you sit. While you are sitting, most of the muscles are inactive.
Inactive muscles weaken over time.
It is the abdominal muscles more than the back muscles that support the spine, and sitting hits them hardest. Another is cramp modern medical science really has no idea what causes cramp, the painful knotting up of muscles. Allopathy tries to cure cramps by way of nutritional therapy. Unfortunately, when the patients stop the nutritional therapy cramps return with more intensity. So now people looking else where for remedies.