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.
A strained chest muscle is really a case of the tendon that attaches muscle to bone, has been stretched a little bit. Tendon is not supposed to stretch, so this is a bad thing. The more it stretched, the worse your pulled chest muscle symptoms will be. A chest muscle tear is where the tendon has ripped at least 5%.