Endurance Training Increases the Amounts of Both Glycogen and Lipid

Endurance training increases the amounts of both glycogen and lipid stored in muscle cells. This most directly increases the

A) shortening velocity of the muscle cells when unloaded.
B) force output of the muscle cells in an isometric contraction.
C) amount of work that can be performed before the cells are depleted of fuel.
D) maximum frequency at which the cells can produce distinct twitch contractions.