A BOSU Balance Trainer, or BOSU ball as it is often called, is a fitness training

Training

The term training refers to the acquisition of knowledge, skills, and competencies as a result of the teaching of vocational or practical skills and knowledge that relate to specific useful competencies. It forms the core of apprenticeships and provides the backbone of content at institutes of...

 device, invented in 1999 by David Weck, consisting of an inflated rubber hemisphere

Sphere

A sphere is a perfectly round geometrical object in three-dimensional space, such as the shape of a round ball. Like a circle in two dimensions, a perfect sphere is completely symmetrical around its center, with all points on the surface lying the same distance r from the center point...

 attached to a rigid platform. It is also referred to as the "blue half-ball", because it looks like a stability ball cut in half. The name is an acronym which stands for "BOth Sides Up" a reference to the two ways a BOSU ball can be positioned. The device is often used for balance

Balance (ability)

In biomechanics, balance is an ability to maintain the center of gravity of a body within the base of support with minimal postural sway. When exercising the ability to balance, one is said to be balancing....

 training. 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, elderly, or injured to the elite level athlete. With the dome side up, the device can be used for athletic drills and aerobic

Aerobic exercise

Aerobic exercise is physical exercise of relatively low intensity that depends primarily on the aerobic energy-generating process. Aerobic literally means "living in air", and refers to the use of oxygen to adequately meet energy demands during exercise via aerobic metabolism...

 activities.
As the name suggests, the device can also be flipped over so that the platform faces up. In this position, the device is highly unstable and can be used for a wide array of exercises as well.

Criticism

In a scientific experiment conducted at Eastern Illinois University

Eastern Illinois University

Eastern Illinois University is a state university located in Charleston, Illinois, United States. Established in 1895 as the Eastern Illinois State Normal School, a teacher's college offering a two-year degree, Eastern Illinois University gradually expanded into a comprehensive university with a...

 in 2009, 12 men performed various physical exercises (back squat

Squat

The word squat, squatter or squatting can refer to:* Squatting, living in an abandoned or unused building, sometimes for political purposes...

, deadlift

Deadlift

The deadlift is a weight training exercise where a loaded barbell is lifted off the ground from a stabilized, bent over position. It is one of the three canonical powerlifting exercises, along with the squat and bench press.-Overview:...

, overhead press, and curl lifts) with and without the BOSU ball. Using the BOSU ball did not create a real difference in the activity of their muscles. Therefore, it was concluded that the BOSU ball did not bring a significant improvement for these physical exercises and that these exercises performed on stable grounds were as efficient as the ones performed on the BOSU ball. A second study which concentrated on single-leg stance shows very similar results (no difference in muscle activity with and without the BOSU ball).