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.
Start exercises to stretch your Achilles tendon as soon as you can do so without pain. The Achilles tendon connects the calf muscles on the back of the lower leg to the bone at the base of the heel. Try the towel stretch if you need to sit down, or try the calf stretch if you can stand.