Baoding medicine balls - also known as "health balls" or "massage balls" - have been used for centuries and used in Chinese culture for their physical and mental benefits.

Here’s what they do:

1. Hand Exercise and Strengthening: Most often, these are used to help with hand exercises. These are great for helping to strengthen the wrist and hand as well as to aid with dexterity and strength.

2. Stress Relief and Relaxation: These are beneficial to help distract the mind as a type of anxiety calmer. By focusing in on the movement, this helps to break any anxious thoughts and refocus.  

3. Acupressure and Circulation: Some people believe that the rolling motion on the balls helps stimulate certain acupressure points in the hands, which can improve circulation, promote relaxation, and enhance overall health. 

4. Mental Focus and Concentration: Because using Baoding balls requires a certain amount of focus and coordination, it can also help improve mental concentration. It’s often a mindful practice, allowing you to focus your attention on the task at hand, which can be meditative in itself.

They often come in pairs, and there are usually different sizes and designs, with some even containing a small bell inside that creates a soft jingling sound as you roll them.