How do differences in Achilles' tendon moment arm lengths affect muscle-tendon dynamics and energy cost during running?

Introduction: The relationship between the Achilles tendon moment arm length (AT) and the energy cost of running (E) has been disputed. Some studies suggest a short AT reduces E while others claim a long AT reduces E. For a given ankle joint moment, a short AT permits a higher tendon strain energy storage, whereas a long AT reduces muscle fascicle force and muscle energy cost but shortening velocity is increased, elevating the metabolic cost.