International Sports Sciences Association (ISSA) Certified Personal Trainer (CPT) Practice Test 2025 - Free CPT Practice Questions and Study Guide

The correct answer is the soleus. The soleus is a muscle that lies directly beneath the gastrocnemius in the posterior compartment of the leg. While the gastrocnemius is the more prominent muscle that gives the calf its shape and looks muscular, the soleus plays a crucial role in plantarflexion of the foot and is essential for activities such as walking, running, and standing.

The soleus is particularly important during prolonged activities because it is capable of sustaining contractions without fatigue, thanks to its high concentration of slow-twitch muscle fibers. This muscle works in conjunction with the gastrocnemius during movements but is quieter in actions that do not involve the knee joint, as it does not cross the knee unlike the gastrocnemius.

In contrast, the anterior tibialis, extensor digitorum longus, and posterior tibialis are situated in different areas and serve different functions. The anterior tibialis is located in the anterior compartment and acts to dorsiflex the foot, the extensor digitorum longus extends the toes and dorsiflexes the foot, and the posterior tibialis supports the arch of the foot and also plantarflexes it. Understanding the specific locations and roles of these muscles helps clarify the