The contractile unit of the myofibril of a striated muscle.
1997, Kenneth Axen, Kathleen Vermitsky Axen, The Princeton Review Physiology Coloring Workbook, Princeton Review Publishing, Random House, page 51,
The sarcomere determines the amount of overlap between the actin and myosin filaments and thus, the number of cross-bridges that participate in a given contraction. Since each cross bridge contributes to the contraction, sarcomeres generate their maximal force when their contraction employs the maximal number of cross-bridges between the actin and myosin filaments.