[Pilates balls to train the core and balance] With its high density and burst protection, the 55 cm diameter TRNR Stability Ball is designed to increase core strength and balance, making it the perfect tool for Pilates movements. This ball works your abs, back, and pelvic floor muscles and improves your posture. This strengthens muscles that are neglected and prevents muscle imbalances, back pain, and possible injuries. Stability balls are also essential for improving coordination, joint stability, and range of motion. It comes with a manual pump and a TRNR dual-purpose tool that makes it easy to inflate the ball to the exact size by aligning the two holes with the marks on the ball, and the fork-like end makes it easy to remove the plug.