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.
Most often, surgery is required to repair the tendon, and after about four weeks in a sling you can begin to strengthen the tendon by working on range of motion exercises -- with your doctor's approval. Start by simply holding your arms out in front of you with your palms facing upward.