What is the maximum tension they can produce in the Achilles tendon? (Muscles are attached to bones by means of tendons. The maximum force that a muscle can exert is directly proportional to its cross-sectional area at the widest point. We can express this relationship mathematically as , where (sigma) is a proportionality constant. Surprisingly, is about the same for the muscles of all animals and has the numerical value of in SI units.)The gastrocnemius muscle, in the back of the leg, has two portions, known as the medial and lateral heads. Assume that they attach to the Achilles tendon as shown in the figure. The cross-sectional area of each of these two muscles is typically for many adults.