BOSU

When the dome side faces up, the BOSU ball provides an unstable surface while the device remains stable.

This combination of stable/unstable allows a wide range of users, from the young,[2] elderly, or injured to the elite level athlete.

The name initially came from an acronym standing for “Both Sides Up" - a reference to the two ways a BOSU ball can be positioned.

[4] In a scientific experiment conducted at Eastern Illinois University in 2009, twelve men performed various physical exercises (back squat, deadlift, overhead press, and curl lifts) with and without the BOSU ball.

[5] A second study which concentrated on single-leg stance shows very similar results (no difference in muscle activity with and without the BOSU ball).