If you were to only perform one weighted stretch for the upper body, shoulder dislocates should probably be it. Daniel Chan from GB Affiliate BodyTree GST in Singapore does an excellent job explaining the intricacies of this movement in the above video. Briefly, use a PVC pipe loaded with a 2.5- or 5-lb weight plate to start, and stand up tall with your hands holding the PVC in front of your body. Keeping your elbows locked and your ribs in, lift the PVC up overhead, continuing all the way behind you until the PVC touches the small of your back. Move slowly and with control, and reverse this movement by lifting the weight (keep your elbows locked!) back up overhead until you reach the start position.
Quality is paramount here, so take your time and do these properly to yield the best results.
Here are the key things to remember:
Weighted mobility differs drastically from your typical stretching routine, but it is necessary given the damage most adults have done to their bodies over time.
Jefferson curls will help build both strength and flexibility in your back, hamstrings, and entire posterior chain.
Shoulder dislocates are one of the best upper-body weighted mobility exercises to bulletproof your thoracic spine.