An exercise devoloped by Dr. Arnold Kegel designed to strengthen the muscles of the pelvic floor especially the pubococcygeal (PC) muscles to increase vaginal muscle tone, improve sexual response, and limit involuntary urine release due to stress urinary incontinence. These exercises are often prescribed following childbirth or during and after menopause. Want to improve your vaginal health? Check out this selection of different types and styles.Ben-wa balls are three-quarter-inch marble-sized balls that you insert into your vagina to increase pleasurable sensations or to exercise your pelvic floor muscles. The original ben-wa balls date back to ancient Japan. Today, there is also a new version called duo-tone balls that are a bit larger—one to one-and-a-half inches— and attached to each other with a strong nylon cord, which can be tugged on for added pleasure. The cord also aids removal. Duotone balls also differ from ben-wa balls in that they are lighter but have a weighted ball bearing inside each ball that helps to create more sensation.Both ben-wa and duo-tone balls are best used for pleasure when combined with other forms of stimulation, such as a vibrator or vaginal intercourse. If you are using them to strengthen your PC muscle, just insert them and walk around. Your PC muscle will have to work to hold them in place. Duo-tone balls would be safer for this because of their size and weight.