What type of exercise is the "Reformer 100's" categorized under?

The "Reformer 100's" is categorized under abs exercises because it primarily focuses on engaging the core muscles, particularly the abdominal muscles. This exercise serves as a warm-up that emphasizes stabilization and control of the pelvis and spine while activating the rectus abdominis and other core musculature. The rhythmic inhaling and exhaling while pumping the arms helps to further engage and strengthen the abs, making it an effective foundational movement in Pilates for developing core strength and endurance.

While the other categories, such as spinal rotation, footwork, and back extension, involve different muscle groups and movements, they do not specifically target the core in the way that the "Reformer 100's" does. Therefore, this exercise is fundamentally linked to abdominal conditioning and is a key component in any comprehensive core-focused workout.