I made 1000-1500 twists / day (+ 300 pumps) with the spring and after 4 months ...... it broke in the middle !! That said; it's been at least 5 springs of different brands I break !!!! Pity THE unbreakable spring does not exist !!!! or they are all done for small random use; but not for an average daily intensive training in !!! I recommend another, because I have no choice !!