Final answer:
During the mid-stance phase of gait, the soleus is the primary muscle active, as it maintains posture and provides stability by resisting gravitational forces when transitioning body weight to the forefoot. The correct option is C.
Step-by-step explanation:
The muscle most active during mid-stance of gait is the soleus. During the mid-stance phase, the soleus is essential for maintaining posture and providing stability. While the gastrocnemius also contributes to plantar flexion of the foot, it is more active when the knee is extended, which is not typically the case during mid-stance.
On the other hand, the tibialis anterior helps with dorsiflexion, and the peroneus longus (fibularis longus) assists in plantar flexion and eversion of the foot.
However, the soleus is predominantly active in resisting the gravitational force when the heel comes off the ground, ensuring that the body's weight can be smoothly transferred to the forefoot. Therefore, the soleus muscle is crucial to the mid-stance phase of gait.
Hence, Option C is correct.