Roll over stability balls, a new study shows they’re not the only way to firm your belly. When Northern Illinois University researchers sized up ab moves done on an inflatable disc, stability ball, Bosu Trainer and bench, the discs took first place activating 24% more muscle fiber than the others. Researchers say balancing on the discs 13inch surface had a tightrope like effect. Better yet. At under $25 the disc was the cheapest solution tested!
Prevention Magazine 2008