Sarcomere stretch beyond 2.2 microns is the physiologic mechanism behind which condition?

In the context of muscle physiology, the sarcomere is the fundamental unit of muscle contraction. The length of a sarcomere optimally allows for the greatest overlap of the actin and myosin filaments, which is critical for efficient muscle contraction. When sarcomeres are stretched beyond approximately 2.2 microns, the overlap between the actin and myosin decreases, leading to reduced force production during contraction. This physiological phenomenon is particularly relevant in the context of heart failure.

In heart failure, the heart muscle may become dilated, leading to an increased length of the muscle fibers. When these fibers are stretched too far, it can impair their ability to contract effectively, resulting in decreased cardiac output and increased work of the heart. This impaired contractility is often linked to the pathophysiological changes that occur in heart failure, where the heart struggles to pump blood efficiently due to the altered mechanics of the sarcomere.

Thus, the relationship between excessive sarcomere stretch and compromised cardiac function underpins the association with heart failure, making this the correct answer. The other conditions listed do not primarily involve the mechanical properties of sarcomeres in the same way heart failure does, as they relate to different physiological processes and systems.