Director of Instruction,
The Golf University ,
Many golfer's create needless worry over trying to keep their left arm straight throughout their swing. This old myth is not only unimportant., It can be downright damaging to your swing.
The only position in the golf swing where it is of relative importance to have your arm straight is at impact with the ball. Even there it is more a matter of letting it happen than trying to make it happen.
The problem arises directly from the set up as golfers tense up their entire left side in an effort to keep their arm straight. This pre swing tension is a killer to their over all swing motion. A tense left arm usually creates an arm dominated swing resulting in a reverse weight shift and a lack of proper shoulder turn. The result is a severe loss of power.
Professional golfers and good amateurs always have relaxed arms at address and frequently have a slight bend in their left arm at the top of their backswing. They are more aware of staying relaxed whereas the average golfer is attempting to remain rigid. Who do you think will have a smoother swing?
The bottom line is not to worry or even think about keeping your left arm straight. It is more important to keep it relaxed, if you do this you will have better rhythm and gain more club head speed. This will translate to the extra distance you have been searching for.