The distance your hands start at address from your shoulders, should remain constant throughout your golf swing.  If your arms bend or come closer to you during your swing, you’ll end up topping or even missing the ball.  Ideally, you want your arms to extend as you strike the ball.  Using a dumbbell can help you feel the extension throughout your swing.  The weight of the dumbbell can help keep your arms extended.

Dumbbell Arm Extension Exercise

Do 8 to 10 repetitions on each side.