If you cannot take your thoracic spine through full range of motion, you will end up over using your shoulder muscles and this may cause injury. You will tend to lift the club up to the top instead of making a complete turn to finish your backswing, leading to power leaks and swing faults.
Lie on your back with you arms by your side and your legs relaxed.
Raise you arms up over your head and drop them behind your head, touching your fingers to the floor. Keep your arms extended.
Keep both shoulders placed on the floor as you hold position for 8 to 10 counts.
Return to start position and repeat for 8 to 10 repetitions.