Ever wonder what that Saturn shaped plastic dome was at the gym? The BOSU balance trainer (an acronym for "Both Sides Up,") is a two-sided exercise device consisting of an air-filled dome molded over a flat, non-skid plastic platform.

Balance Blaster — Why It Matters

Many gym goers have probably seen someone balancing precariously on such a device while attempting to juggle monkeys, perform bicep curls, or both at the same time (trust me, this really works the core). The BOSU's "secret sauce" is that it claims to add an element of instability to exercise, strengthening key stabilizing muscles and creating a stronger foundation for all movement Core stability: the centerpiece of any training program. Bliss LS, Teeple P. Northwest Sports & Spine, 105 West 8th Avenue, Spokane, WA. Current Sports Medicine Reports. 2005 Jun;4(3):179-83.. Movements can be performed on the dome or the platform, as well as in a standing, seated, kneeling, or lying position. Because the BOSU is closer to the ground and less mobile, exercises are potentially safer than those performed on a traditional Swiss ball (but certainly less useful on the journey to becoming a world-renowned circus elephant) Effect of surface stability on core muscle activity for dynamic resistance exercises. Yaggie, J.A., Campbell, B.M. Applied Biomechanics Laboratory, Department of Exercise and Nutritional Sciences, San Diego State University, San Diego, CA. Journal of Strength and Conditioning Research. 2006 May; 20 (2):422-8..

However, several studies have raised doubts as to the effectiveness of the device, which normally runs upwards of $100. Studies suggest performing compound weight training movements on is no more effective in engaging the core than the same exercises performed on stable ground Not all instability training devices enhance muscle activation in highly resistance-trained individuals. Wahl, M.J., Behm,D.G. School of Human Kinetics and Recreation, Memorial University of Newfoundland, St. John's, Newfoundland, Canada. Journal of Strength and Conditioning Research. 2008 Jul;22(4):1360-70. Deadlift muscle force and activation under stable and unstable conditions. Chulvi-Medrano I, García-Massó X, Colado JC, et al. Department of Physical Education and Sports, University of Valencia, Valencia, Spain. J Strength Cond Res. 2010 Oct;24(10):2723-30.. And despite its wobbly nature, performing standing movements on either side of a BOSU might even be ineffective at creating extra work for the ankles Ankle muscle activation when using the Both Sides Utilized (BOSU) balance trainer. Laudner KG, Koschnitzky MM. Biomechanics Laboratory in the School of Kinesiology and Recreation, Illinois State University, Normal, Illinois. J Strength Cond Res. 2010 Jan;24(1):218-22..

Core Concept — The Answer/Debate

But BOSU's claims aren't entirely without backing. One study testing BOSU’s effect on enhancing long jump and shuttle run performance suggests the device might improve performance in balance and posture tests, but it's unclear whether the improvement carries over to all functional movement Effects of balance training on selected skills. Yaggie, J.A., Campbell, B.M. Applied Biomechanics Laboratory, Department of Exercise and Nutritional Sciences, San Diego State University, San Diego, CA, Journal of Strength and Conditioning Research. 2006 May; 20(2):422-8..

When it comes to BOSU, some people swear by it, while others, well, swear at it. Though the BOSU's effectiveness is unclear, it's a cute, colorful piece of equipment that can add variety to a range of workouts. This balancing act might be worth a try!

Updated August 2011