Final answer:
Force increases as velocity of shortening increases due to the length-tension relationship in the sarcomeres of muscles.
Step-by-step explanation:
Force increases as velocity of shortening increases due to the length-tension relationship in the sarcomeres of muscles. When sarcomeres reach their optimal lengths, they contract more powerfully because more myosin heads can bind to actin, forming cross bridges and increasing the strength of contraction. If sarcomeres are stretched beyond their optimal lengths, the force of contraction would decrease.