Early extension is one of the most common swing characteristics I see with students of all levels. If you're losing power and hitting it too low - then this applies to you. Early Extension can be defined as excessive movement of the pelvis towards the ball (target line) during the swing. Though we often associate early extension with a loss of consistency, the loss of power and spine angle is just as significant.
Centripetal force is defined as "a force that acts on a golf club moving in a circular path and is directed toward the center around which the golf club is moving." The concept of centripetal force is ubiquitous in sports, especially rotational activities. Watch how a hammer thrower accelerates the implement by remaining centered in the ring. This is a great illustration of centripetal force.
So what does centripetal force look like in the golf swing?
Below are three elite golfers: Jimmy Walker (left), Dustin Johnson (center), and World Long Drive champ Justin James (right). A vertical line is drawn behind their tailbone as a reference point. As you can see, Jimmy Walker (the shortest hitter) moves off the line, while DJ's hips stay on the line and Justin's actually move past the line (away from the target line).
Jimmy Walker isn't a short hitter by any means, but he's forced to rely on his wrist angle to keep up with the longest in golf. Put it this way: turn on a World Long Drive event and watch the lower bodies. They always move away from the target line like Justin James. This is a great illustration of a phenomenon called parametric acceleration. By pulling inward at the impact stage, James is able to create additional acceleration of the club.
We're careful to refer to early extension as a swing characteristic and not a swing fault because it doesn't preclude players from playing great golf. Early extension hasn't stopped Zach Johnson and Jimmy Walker from winning major championships, flying private and paying cash for large homes. That said, early extension requires golfers to make compensations at impact.
So, if you're losing power and you're moving towards the target line (ball) - you're going to have a change in posture (hitting the top of the ball - not creating a negative attack angle) and lose power.
Drills to Fix:
Drill 1: Practice with your back against a box or wall - take your backswing feeling pressure on your behind (right side), and on the downswing, try push the box or wall with your behind (left side). The red dotted line in the image above will help you visualize the wall or box.
Drill 2: You're taking the club back on a good swing plane, then starting down too steep, which causes you to self adjust, thrust body towards the ball to try and shallow out and by this time its too late - your posture has changed and you're losing power. Simply learn to swing the club on a good plane - baseball swings will help you achieve this.
EARLY EXTENSION - As you approach impact, you lose your original address posture and spine inclination to the ground, which causes you to lose power and practically swing over the top of the ball. This is often caused by the urge to help the ball into the air. This faulty movement pattern causes the arms to get stuck behind the body, forcing the upper body to rise through impact.