The length of a muscle at which tension is maximum is called:

When a muscle at rest is stretched, its sarcomere length is changed. When this muscle is made to contract from the various lengths at rest, contractile force developed varies according to the actin-myosin interaction possible within the sarcomere. Resting length of sarcomere = 2 m. This is Li or length initial. Contractile force increases as muscle length is increased up to a point. Sarcomere length of 2.2 m obtains maximum force of contraction. (Starling's law: Greater the fiber length, stronger will be the contractile force). This is Lo or length optimum. At this length, there is optimum interdigitation between actin and myosin.