An exercise ball, also called a Swiss ball or stability ball, is an inflatable sphere with a diameter of 55 to 75 cm. Sitting or performing exercises on the ball activates deep core stabilizers because the unstable surface constantly challenges balance. It is used for core training, prenatal fitness, physical therapy, and active sitting. Burst-resistant models are available for safety. The ball can support stretches, crunches, planks, and balance drills. It is a low-cost, space-saving tool that adds variety and difficulty to bodyweight workouts while improving coordination and posture.