Fitter First DuraBall PRO Exercise Ball Blue or Silver(75cm) World's Strongest Exercise Ball Chair. Strongest and safest burst resistant exercise ball. Its perfect for larger individuals and is also suitable as a ball chair when underinflated. Burst Resistant up to 1,100 lb and Static Load Rating of 4,400 lb. Available in 45 cm,55 cm,65 cm,75 cm,85 cm sizes with diffrent colors.