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.
Stretch or Rest a Torn Muscle? Let' say you tore a muscle. What should you do? Well, like anything, it depends on the details. If the tear is deep, and it burns when you even approach stretching it, take time off. Massage the muscles, or get a professional massage therapist to work on it. The Homeopathic remedy Arnica Montana (30x strength) is for sore muscles and bruises, and taken as directed, can help that muscle heal.