Questions: The amount of tension produced by an individual muscle fiber depends solely upon which of the following factors? The number of pivoting cross-bridges A longer latent period The presence of summation The length of the contraction phase

The answer is the first one: the number of pivoting cross-bridges.

Explanation for each option:

1. The number of pivoting cross-bridges: Correct. The amount of tension produced by an individual muscle fiber is directly related to the number of cross-bridges that are actively engaged in the contraction process. More cross-bridges result in greater tension.

2. A longer latent period: Incorrect. The latent period is the time between the initiation of a stimulus and the beginning of muscle contraction. It does not directly affect the amount of tension produced by the muscle fiber.

3. The presence of summation: Incorrect. Summation refers to the increased force of contraction that occurs when a muscle fiber is stimulated repeatedly before it has a chance to fully relax. While summation can increase overall muscle tension, it is not a factor that affects the tension produced by an individual muscle fiber in a single contraction.

4. The length of the contraction phase: Incorrect. The length of the contraction phase refers to the duration of the muscle fiber's contraction. While it can influence the overall performance of the muscle, it does not directly determine the amount of tension produced by an individual muscle fiber.

Summary: The amount of tension produced by an individual muscle fiber depends solely upon the number of pivoting cross-bridges.