If you, or someone you know, has ever had heart surgery, the surgeon may have accessed the heart by cutting the sternum vertically down the midline and spreading it apart. Afterwards, the 2 halves of the sternum are wired shut to encourage the cut halves of the sternum to stay pushed closely together while they heal.

This was probably followed up with advice to limit movements of the trunk and limbs to protect their sternum while it heals. To a large extent, these 'sternal precautions' were based on a fine logical argument but - like so many things we think we understand in the human body - it is always better to test such ideas to be sure they work as anticipated.