Change in length. At an intermediate sarcomere length, Lo, the amount of overlap between actin and myosin is optimal and the relative force is maximal. • When the sarcomere is stretched beyond the length at which the thick and thin filaments overlap (length a), cross bridges cannot form and no force is exerted.• As sarcomere length decreases and the overlap of the thick and thin filaments increases (between lengths a and b), the force increases because the number of cross bridges increases.• With further reductions in length (between lengths c and e) the extreme overlap of the thin filaments with each other occludes potential attachment sites and the force decreases.