A dancer's knees are the life line to ballroom dance. Flexibility is essential and even the smooth dances call for a softness of the knees to accompany the rise and fall of most figures.
Dancers should always be aware of the kind of floor they dance on. Competitions are held on a floating wood floor that is comfortable to the dancer's knees. Dancers avoid practicing on cement, tile or any rigid surface that jars the knees.
Knees can quickly end a dancing career and it's sad when a dancer has to retire the dancing shoes to the garage. Social dancers, too, should be aware of their dancing surface and the knees will take them dancing into old age.
Below is a video of a Samba . Note the work-out on the knees. Samba is "sooo much fun." One great reason to keep your knees healthy. The vid is long... just take a peek. (or not)