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Spine angle simply means the angle that you create with your spine in your address position. This angle affects your swing plane, or the angle that you swing the club head of the golf club around you on.
Your swing plane angle influences the consistency of your strike and the accuracy of your golf shot so it is crucial to create and maintain the correct spine angle if you want to improve your golf.
To create the correct spine angle as you address the golf ball, you need to maintain a completely straight back and tilt, or hinge forward from your hips towards the ball, with your upper body. To achieve this place an alignment pole down the back and inside of your t-shirt. Tuck the pole into the belt of your trousers and this will now create a straight position with your back. You need to have the back of your head, middle of your shoulders and bottom of your back all in contact with the alignment pole. From this position of standing directly upright, position your feet shoulder width apart and then tilt forward from your hips towards the golf ball.
As you do this, ensure that you maintain contact with the alignment pole on the back of your head, middle of your shoulders and the bottom of your back. Tilt forward enough so that your arms are able to hang freely and directly under your shoulders, away from your body. Now maintain this position and soften your knees, to take the pressure from the back of your legs and make your address position more comfortable. If you do not have an alignment pole, you could work on this drill with the shaft of your golf club held down your back from your head.
From this position, you will now be able to rotate around the axis that you have created with your spine as you swing your golf club and by rotating around your spine as you swing, you will become more consistent with how you swing the golf club.
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The angle that you set with your spine in your address position directly influences the angle that the club head travels around you on as you swing your golf club. If you are too upright with your spine angle at address, then the club head will travel too steeply around you. If you curve your spine forward, you will not be able to simply rotate around your spine and as a consequence you will put additional movement into your swing by straightening your spine into a vertical position. If you bend forward and create too much spine angle, you will swing the club head too flatly around you. All of these will give you issues with strike and accuracy.
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If you create too much spine angle in your address position, then you will swing the club head on too flat a plane around you. The angle that the club head travels on during the swing will be too low and as a result you will approach the golf ball too much on the inside target line which will make it very difficult to swing the club head directly along the target line, a requirement of hitting straight shots.
Sorry Try Again! - See Explanation Below
If you curve your spine when taking up your address position then this makes it very difficult for you to rotate your upper body around your spine. Rather than rotating your upper body, you will tend to lift your arms and straighten your spine as you swing and this upward movement in your body will make it difficult to achieve a consistent strike with the club head tending to impact the top of the golf ball with this action.