Final answer:
The ability to exert maximal muscular contraction in an explosive burst of movements defines muscular power. Fast-twitch fibers and the somatic nervous system are key elements in developing this type of fitness, which is crucial for activities like sprinting and jumping.
Step-by-step explanation:
The ability to exert maximal muscular contraction instantly in an explosive burst of movements is a type of muscular fitness called power. Power is a critical component of fitness, particularly for athletes involved in activities that require a sudden burst of high-intensity effort, such as sprinting, jumping, or weightlifting. Within muscle physiology, the fast-twitch muscle fiber is crucial for these explosive movements, as they are primarily responsible for anaerobic activities, meaning they operate without relying heavily on oxygen.
Exercises that emphasize muscle contractility—the ability to shorten or contract forcibly—such as sprints, help to develop power. During the contraction phase, particularly the twitch contraction phase, tension in the muscle increases rapidly, resulting in the explosive force required for activities demanding power. The sprinter's need for a quick, intense energy burst cannot be met by aerobic cellular respiration, instead relying on anaerobic glycolysis, associated with the fast glycolytic (FG) muscle fiber.
Moreover, muscle contraction speed is a factor influenced by the nervous system, particularly the somatic nervous system. This system responds to local muscle and joint conditions, allowing athletes to generate maximum contraction speed and, consequently, power, during their performance. Thus, the correct answer to the original question is 'a. power'.