Why should you stretch?
Stand in the doorway. Have both forearms touching the threshold of the doorway. The upper arms should be out straight. Push out for 5 seconds. Fall forward for 5 seconds. Repeat 5 times.
Another variation is to start with the upper arms out straight. Repeat the exercise twice. Then raise the arms up the doorway by 2 inches. Repeat the exercise 2 times. Then raise the arms even higher and repeat 2 more times. The higher that you raise the arms, the lower down the ribcage and chest wall that you are stretching.
The psoas muscle stretching exercise