-- Last Updated: Dec-12-12 5:04 PM EST --
Flex can come from the blade, the shaft, or both.
Too little flex and you may begin to feel it in your bands, wrist, and shoulders. When switching to a paddle with less flex, you may notice that the paddle feels stiff and a little bit "dead" in your hands. A stiffer paddle is more efficient and therefore well-suited for anyone looking to get a boost in speed or power.
A moderate amount of flex gives a paddle a lively feel. The paddle provides a crisp little "snap" at the end of the stroke. It can be more forgiving on the joints and is well-suited for long-distance touring.
Too much flex results in a loss of power and efficiency. No one wants to propel their boat with a noodly paddle -- but there are some of these paddles out there. These paddles are usually in the less expensive -- and that is probably their only asset.
I don't know of any manufacturer using a rating system for paddle flex -- but it's a good idea.