Spring washers, sometimes called disc springs, are a subtype of washers. They lend their mechanical capabilities to the unique profile of the material: when subject to a load, the irregularities of the washer compress with a proportionate resistance to return to their predeflected shape.
You should never stretch a pulled muscle to the point of pain or you risk re-injuring it. Do not overstretch the pulled muscles. Too much stretching can retear injured muscle fibers. Gently stretching a pulled muscle may relax the surrounding muscle fibers, which may be tight in response to the injury.
Go deeper into the stretch under your shoulder blade by pulling the pole forward with your left hand. Pull until you feel a stretch under your shoulder blade. Breathe normally as you maintain the stretch for 15 to 30 seconds. Slowly release, and repeat two to four times. Complete the stretch on your left side.