Which statement about preload and contraction is correct?

• A. Higher Preload Decreases Contraction Force
• B. Preload Has No Effect On Contraction Force
• C. Preload Increases Contraction Force
• D. Afterload Controls Contraction Force

Answer: (A)

The idea being tested is how preload affects the force of contraction in the heart. Preload is the stretch placed on the cardiac muscle when the ventricle fills. As preload increases, the muscle fibers are stretched toward their optimal length for contraction. This length-tension relationship means more cross-bridge overlap between actin and myosin during systole, so the heart contracts with greater force and ejects more blood—up to a physiologic limit. That’s why preload generally increases contraction force.

If preload is too high, the fibers can be overstretched and contraction becomes less efficient, but under normal conditions a higher preload enhances the contractile strength. The statement that preload has no effect on contraction is incorrect, and the idea that higher preload decreases contraction force misreads the length-tension relationship. Afterload, while important to how much blood is ejected, is a different factor and does not define the direct effect of preload on contraction force.