Extra Ball for the Classic Balance Ball® Chair (52cm)Our ergonomic, latex free, anti burst 52cm fitness ball keeps your spinal alignment and core strong while you work when used in our Classic Balance Ball Chair. When used alone it is also great for fit ball exercises, core workouts, stretching and as a Pilates balance ball. Even the kids can improve their balance, abdominal strength and overall fitness. Only ball made to fit Balance Ball Chair Improves balance and fitness Strengthens core muscles