The question came up in today's Prenatal Yoga Class, "Does double-jointed mean you have double joints?" My answer: "No, it just means that a particular joint is very flexible."
In case I didn't explain myself sufficiently and for others who may have the same question, the term double-jointed refers to hypermobility (able to bend beyond the normal range) within a joint.
Some recent studies suggest that being hypermobile protects you from the ravages of arthritis. Although they are not clear if it is due to exercise induced stretching, or if hypermobile people tend to exercise and stretch more.
In the interest of body balance, it makes sense to strengthen the muscles that surround a hypermobile joint as much as we seek flexibility in our strong and/or shortened muscles. These factors become even more of a focus for the pregnant woman whose hormones cause her joints to become more flexible. Yoga during pregancy addresses the strengthening of these areas as well as stretching and relaxation issues.