When a ballerina balances on her tip toes, what movement is she performing and which muscle is used?

The movement a ballerina performs when balancing on her tiptoes is plantar flexion, which occurs at the ankle joint. In this position, the toes point downward as the heel lifts off the ground. This movement is primarily facilitated by the gastrocnemius muscle, which is one of the two main muscles that make up the calf (the other being the soleus).

The gastrocnemius is responsible for generating the force necessary to raise the heel and maintain balance during this position. Thus, the combination of plantar flexion and the involvement of the gastrocnemius muscle makes this the correct answer.

In contrast, the other options reference movements or muscles unrelated to the action of rising onto the tiptoes. Eversion and inversion pertain to the movements of the foot primarily around the frontal plane and involve different muscle groups, while dorsiflexion would involve bringing the toes closer to the shin, which is the opposite of what occurs during tiptoeing. Hence, recognizing the specific movement and its associated muscle helps in understanding the biomechanics of the activity.