The medicine ball allows a individual to train their entire body three-dimensionally. It is a versatile training devise that can be used as a warm-up, complete workout and/or cool-down. You can adjust the exercise’s speed, range of motion, resistance, and your body position quickly and easily. The options are virtually endless.

 

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Why is it called a medicine ball?:
Medicine ball training is one of the oldest forms of strength and conditioning training – the first reference to wrestlers training with sand filled bladders appears in Persia nearly 3000 years ago. In ancient Greece the physician Hippocrates had them sewn out of animal skins and stuffed with sand. His patients threw them back and forth for injury prevention and rehabilitation.
In the late nineteenth century and early twentieth century, the words "health" and "medicine" were synonymous. The so-called "Four Horsemen of Fitness" were the dumbbell, the Indian club, the wand and the medicine ball. This is where the beginnings of the modern medicine ball originate.

Excerpt from www.wikipedia.org