Shaft Flex
“Flex” refers to the ability of a golf shaft to bend as forces are applied to it during the golf swing. These forces are generated by the type of swing that you have – fast or slow, smooth or jerky. There are five generally used ratings for shaft flex: Extra Stiff, Stiff, Regular, Senior and Ladies, usually denoted by the letters X, S, R, M and L (“M” is used for Senior because this flex stands for medium/mature). How much or how little a club’s shaft flexes plays a major role in how and when the clubface is squared at impact. It is important to have the proper flex for your swing speed. Without it, there’s a good chance that you’ll have a hard time making good solid contact on a consistent basis, thereby affecting both the direction and distance of the golf shot.

WHY FLEX MATTERS
A shaft that is too weak will flex excessively throughout the swing, therefore creating an inconsistent release point. The result is a shot that produces too much spin, and the golf ball will travel in many different directions. Mostly the ball will draw (right-to-left for right-handed golfer) and go very high.