Which substance is primarily stored in muscles and used for energy?

Muscle glycogen is primarily stored in muscles and serves as a key source of energy during physical activity, particularly during high-intensity exercise. Glycogen is a polysaccharide that is made up of glucose molecules, which can be rapidly mobilized when energy is needed for muscle contractions. When you engage in physical activities, especially those that require short bursts of energy, the body taps into these glycogen stores to fuel those efforts.

While creatine can enhance energy production in muscles by regenerating ATP (adenosine triphosphate), it is not stored as a primary energy source like glycogen. Protein serves various roles in the body, including muscle repair and growth, but it is not the main energy substrate utilized during exercise. Fat deposits can serve as a long-term energy source, especially during lower-intensity, prolonged activities; however, they are not as readily available for quick energy needs as glycogen. Thus, muscle glycogen stands out as the primary substance stored in muscles specifically for energy during exercise.