This stretch is done from your single axis address position but a golf club is not needed. It is best done in a mirror the first few times so you can check positions. From your single axis address position (and simulated grip position) slide your trail hand up and grab your lead wrist. Slowly move to into your backswing making sure you are:
Keeping your lead foot planted on the ground Maintaining the flex in your trail knee Keeping your lead arm straight Maintaining your spine tilt
Stop when you feel mild tension (you could literally feel it anywhere, I’ll explain in moment), pause and begin your slow, deep breaths. After two slow, deep breaths use your trail hand to extend your lead arm out slightly further, MAKING SURE that none of the above has been compromised. Hold this position for at least two more breaths. Extend your stretch one more time as long as you don’t break down any of the above positions. Hold the stretch for 5 – 10 slow, deep breaths.
Depending on your specific flexibility issues you may feel this stretch in any number of places probably along your lead side: your lead hip flexor; your lead side / rib cage; your lead shoulder; or your lead triceps area. Someone with tight hip flexors will often reverse pivot during their swing to compensate.
Use this stretch to find your tight spots and personalize your stretching routine to improve your swing.
All of the stretches we have covered to date are geared towards helping setup to the ball correctly and swing the club like Moe.