Final answer:
Increasing preload shifts the force-velocity curve to the left and increases the maximum velocity of shortening (Vmax) for cardiac muscle, in line with the Frank-Starling mechanism.
Step-by-step explanation:
The question pertains to the force-velocity relationship in cardiac muscle, which is governed by the Frank-Starling mechanism. According to this law, the force of heart contraction is directly proportional to the initial length of the cardiac muscle fiber, which is to say, the ventricular preload. An increase in preload enhances the stretch of ventricular muscle fibers, leading to more forceful contractions and increased stroke volume (SV) as the ventricles pump more efficiently.
Relating this to the force-velocity curve, which is a graphical representation of the velocity of contraction at varying levels of afterload for a given preload, an increase in preload shifts the force-velocity curve to the left and leads to a higher maximum velocity of shortening (Vmax). This is because muscle fibers operate with greater force, enabling the heart to eject blood more rapidly when preload is increased, within physiological limits. Thus, the correct answer to how increasing preload changes the force-velocity curve is C) Shifts it to the left and increases Vmax.