When Lifting a Heavy Object, the Strength of Leg Muscle

When lifting a heavy object, the strength of leg muscle contractions is determined by the

A) number of calcium ions released by the sarcoplasmic reticulum.
B) number of thick and thin filaments involved in each sarcomere during contraction.
C) amount of ATP used by each active sarcomere during muscle contraction.
D) frequency of action potentials and number of muscle fibers stimulated.