What is the primary muscle worked during the Pilates exercise "The Hundred"?

The primary muscle engaged during "The Hundred" is the rectus abdominis. This exercise focuses on core strength, stability, and endurance, with an emphasis on activating the abdominal muscles. The rectus abdominis, often known as the "six-pack" muscle, plays a crucial role in flexing the spine and stabilizing the pelvis during movements performed in this exercise.

In "The Hundred," participants lift their head, shoulders, and legs off the floor while pumping the arms. This position requires the rectus abdominis to work intensely to maintain spinal flexion and support the upper body while the lower body remains elevated. The rhythmic arm movements in conjunction with the breath pattern further challenge the core stability, relying primarily on the strength of the rectus abdominis.

While the other muscles mentioned contribute to the overall stability and control during Pilates exercises, none are as directly involved in the primary action of "The Hundred" as the rectus abdominis. Therefore, identifying it as the main muscle worked in this exercise is accurate and highlights the focus on core conditioning that is central to Pilates practice.