There are no end to end connections between muscle fibers. A motor unit is made up of a single nerve axon and the muscle fibers it supplies. Muscle fibers in a motor unit have the same contractile and metabolic properties. The amount of active tension that a muscle produces has been shown to be proportional to the fiber type content, so that muscles with higher proportion of type II fibers are able to generate more force. A large portion of muscle activity occurs in an eccentric fashion.
Muscles often contract eccentrically to absorb kinetic energy and protect joints.
For example, as an individual lands from a jump, the quadriceps muscle contracts, protecting the knee. The area responsible for this force transmission is the myotendinous junction, a specialized region of highly folded membranes at the muscle-tendon interface. All rights reserved.