In baseball as in golf, it is common to find many performers having bent arms at the moment of contact. According to these players this is more effective than having straight arms. But is it really so?
From physics we know that having bent arms allows for faster rotation of the body as well as faster movement of the arms. Having a straight arm leads to slower rotation and movement but it also allows for greater power (in comparison to the power achieved with bent arms) at the end of the movement.
Is one preferable to the other? This of course depends upon the situation. When executing a swing, bent arms allow for a faster swing. However when contact is made with the ball the arm should be straight for more power.
Thus you need a combination of both to have a most effective swing. In reality however, few players especially in baseball, achieve full arm extension at the moment of contact. Most have bent arms mainly because of the “sit and spin” type swing.
Baseball players who hit for average and most golfers typically have straight arms at contact. You may now be thinking that this statement is somewhat contradictory in regard to the baseball players. If they have bent arms, how can they be hitting so many home runs?
The answer is simple. They rely on greater rotation speed for production of force rather than straight arms. Sometimes you can even see a combination of both. However, it should also be noted that regardless of whether the arms are straight or bent at contact, the hit and spin type hitter has more strikeouts.
It should also be noted that having bent arms at contact leads to more wrist action which is most often a negative if you rely on this action for more accuracy. For greater accuracy you should have straight arms especially in golf. The more “wristy” the swing, the less is the accuracy.
For more information on the role of the wrists and arms see Build a Better Athlete and Explosive Golf