When muscle cells can slide easily past each other, movement is smooth. If certain cells or muscle fibers adhere to each other, a muscle may have difficulty shortening as well as lengthening. Any time muscle fibers get clumped together, the muscle will be prevented from easily lengthening or shortening. A muscle can get stuck in an extended position, a situation I see fairly frequently with the pectoral muscles of a horse, and the triceps. A buckling may occur on shortening: think of a rug getting wrinkled.