I use prone cobra exercise for thoracic spine and lower traps. I want to apply progressive overload to this exercise. How can I add resistance properly to this exercise? Resistance bands, dumbbells any ideas are appreciated...
To answer your question you could try a weight vest to put more weight on your shoulders increasing resistance off of the ground. You could also try this position on top of a bosu ball to add instability.
That being said I would recommend trying other exercises that can work the same muscles. One particularly good exercise is the back hyperextension but this requires a specific machine. Personally I have have a lot of success in the past with this and you can increase load by adding a plate.
A no equipment version that will also help with shoulders is the superman. Basically instead of holding the position you keep arms straight and rotate them until they meet above your head and then rotate them back behind your back. Do 30 straight of these and you'll feel it in your lower back and shoulders. Aquamans are also effective. (My descriptive skills are lacking but check out youtube.)
The Bodybar, also know as a weighted workout bar, is an under-utilized exercise prop. My gym has a set of them, and I'm the only person who utilizes them. I've incorporated them into many movements, such as squats and lunges. I think you could use a bodybar in the superman. I would grip it wider than your shoulders, straighten your arms, hold it out in front of your head as high off the floor as you can, then go into the superman position. At the gym tommorrow, I'll try it out and tell you how it works.
When you do a superman, you want to protract your scapulas. If you use a dumbell in the superman, with the dumbell in front of your head, then your scapulas will rotate upwards (towards your head), which prevents protraction. (You can't do scapular upward rotation and protraction at the same time.) The advantage of a body bar is that you can grip it wider than your shoulders, and as a result you'll be able to minimize scapular upward rotation, and you'll be able to pull your scapulas deep into protraction.