Final answer:
Muscle stiffness in an undamaged muscle is often caused by overuse and fatigue, not by a lack of hydration, poor nutrition, or muscle atrophy(option b).
Step-by-step explanation:
Stiffness in an undamaged muscle is often due to overuse and fatigue(option b).
Muscle fatigue occurs when the muscle can no longer contract effectively in response to signals from the nervous system. Causes of muscle fatigue include reduced ATP reserves which are essential for muscle contraction, lactic acid buildup leading to lower intracellular pH, and imbalances in ions like Na+ and K+ disrupting Ca flow necessary for muscle action. Moreover, long periods of intense exercise can lead to damage of muscle structures such as the sarcoplasmic reticulum (SR) and sarcolemma, impairing Ca regulation and contributing to muscle fatigue and stiffness. Conversely, muscle atrophy, which might be suggested by answer D, usually results from disuse or aging, and while it does lead to muscle weakness and a decrease in muscle mass, it is not commonly associated with stiffness, particularly in an undamaged muscle.