Muscle
Types Skeletal of Contraction: 1. Isotonic the muscle contracts developing tension so that the muscle shortens as the attachment points (origin and insertion) are brought together. Energy is expended as myosin and actin slide past one another. Example, flexing your arm. 2. Isometric the muscle develops tension, however this is no noticeable relative movement of the attachment points. Energy is expended as myosin and actin bind, but there is minimal sliding of the actin past the myosin. Example, making a muscle. Elastic Elements: Skeletal muscles have elastic properties that can be modeled as springs in series and in parallel to the body of the muscle. 1. Elastic Series Component (SEC) this is modeled as a spring in series with the tendon. All tension exerted by the muscle on the bones must pass through the SEC. Whenever the muscle develops tension, the SEC stretches. The SEC shortens during relaxation. The SEC also stretches when the muscle is stretched which also increases the tension. 2. Parallel Elastic Component (PEC) this is modeled as a spring buried in the body of the muscle from tendon to tendon. As the muscle contracts, it compresses this spring. During relaxation the spring gives up energy. The PEC stretches when the muscle is stretched and returns to its resting length when the tension is removed.