Which muscle group primarily consists of fast twitch fibers used for explosive movements?

The gastrocnemius muscle is primarily composed of fast twitch muscle fibers, which are specifically adapted for explosive movements. Fast twitch fibers, also known as Type II fibers, are capable of generating a lot of force in a short amount of time, making them ideal for activities that require strength and speed, such as sprinting or jumping.

The gastrocnemius muscle, located in the back of the lower leg, plays a significant role in movements such as running and jumping, where rapid and forceful contractions are necessary. This muscle's ability to produce fast, explosive power is particularly pronounced during activities that require quick acceleration and sudden bursts of strength.

In contrast, the soleus muscle, while also important in lower leg movement, is more comprised of slow twitch fibers, which are better suited for endurance activities. Similarly, the hamstrings and deltoids contain a mix of both fiber types, but they do not primarily consist of fast twitch fibers. This distinction solidifies why the gastrocnemius is the correct answer in this context, as it is specifically associated with explosive athletic performance.