**Core Concept**
The question is testing the student's knowledge of the types of muscle fibers present in different muscles. Muscle fibers are classified into three types: Type I (slow-twitch, red fibers), Type IIa (fast-twitch, intermediate fibers), and Type IIx (fast-twitch, white fibers). The proportion of these fibers varies among different muscles, influencing their function and fatigue resistance.

**Why the Correct Answer is Right**
The correct answer is based on the principle that muscles involved in endurance activities have a higher proportion of Type I fibers, which are more resistant to fatigue. The muscle with the maximum proportion of Type I fibers is the **soleus muscle**, which is responsible for maintaining posture and is involved in activities requiring sustained contraction, such as standing and walking.

*Option A:* Incorrect because the **tibialis anterior muscle** has a higher proportion of Type II fibers, which are more suited for fast, powerful contractions.
*Option B:* Incorrect because the **gastrocnemius muscle** has a mix of Type I and Type II fibers, but not the maximum proportion of Type I fibers.
*Option C:* Incorrect because the **rectus femoris muscle** has a higher proportion of Type II fibers, which are more suited for fast, powerful contractions.

**Clinical Pearl / High-Yield Fact**
The proportion of Type I fibers in a muscle can be an important consideration in rehabilitation and exercise programs, particularly for patients with muscle imbalances or chronic fatigue.

**Correct Answer:** C.