Final answer:
The preparatory phase for quick actions in sports primarily activates fast-twitch muscles. These muscles are designed for rapid, powerful movements, contrasting with slow-twitch muscles, which are better for endurance and efficiency over prolonged activities.
Step-by-step explanation:
The preparatory phase of throwing, kicking, or striking is based upon activating fast-twitch muscles, which are essential for rapid movements such as the quick actions in sports. These muscle fibers are specifically designed for short bursts of speed and power. In comparison, slow-twitch muscles are more efficient at using oxygen to generate more fuel (known as ATP) for continuous, extended muscle contractions over a long time, which is why endurance athletes, like marathon runners, have a higher percentage of slow-twitch muscle fibers. Synergistic muscles assist the prime movers in the movement and stabilize the joints, ensuring a smooth and coordinated action.