The Body Can Control the Strength of Leg Muscle Contractions

The body can control the strength of leg muscle contractions when lifting a heavy object by increasing or decreasing the:

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