What muscle group is primarily engaged during the exercise called "Breast Stroke"?

The primary muscle group engaged during the Breast Stroke exercise is indeed the Erector Spinae. This group of muscles is essential for spinal extension, which is a key movement during the exercise. As the participant lifts their torso and reaches their arms forward (simulating a swimming motion), the Erector Spinae works to stabilize the spine and maintain proper posture. This engagement is crucial for facilitating the movement while minimizing the risk of lower back strain.

In contrast, other muscle groups mentioned in the options serve different primary functions. For instance, the glutes are more involved in movements that require hip extension, the hip flexors are responsible for lifting the thigh toward the torso, and the Transversus Abdominus plays a role in stabilizing the core rather than directly influencing spinal extension, which is the focus during the Breast Stroke. Thus, understanding the role of the Erector Spinae in this exercise is vital for achieving the correct form and maximizing the benefits of the workout.